Report for experiment 29 reactions in solution i precipitation answers

On the other hand, ozone reactions in nonaqueous systems have been studied thoroughly, mainly because of Decomposition reactions are initiated by the addition of energy. Experiment 2 Volumetric Analysis 3 . 5 – 6) as you carry out the procedure on page 4. Very similar amounts of work are put in for a very small (as in this experiment) amount of product and a more reasonable (five or six times this experiment) amount of product and less product is lost as well. Oxalic acid and sodium carbonate are some examples. We will first prepare a standard solution of NaOH. This is a reaction where two soluble salts are added together and the result is the precipitation of a single product while the other product remains in solution. 150 M. In this experiment we were able to calculate limiting Experiment 4: Synthesis of Alum from Scrap Aluminum Objective: In this experiment, you will be converting the aluminum metal from a beverage can into the chemical compound potassium aluminum sulfate, KAl(SO 4) 2•12 H 2 O, commonly referred to as alum. HWK: W/S(back): Identifying Types of Chemical Reactions — correct Analysis & Conclusion TEXT p214 #1-5, 7, 14a-d, 15 TEXT p174-175 #4, 6, 13a-g, type of reaction for each part of #13 I conducted a titration experiment a few days back and was unable to neutralize the solution in time, so I had to leave the solutions of HCl and NaOH out overnight in order to use them the next day. The report should include: methods to reactions that occur in solution 7. 2. The standard solution is usually added from a graduated vessel called a burette. b) Add a few drops of silver nitrate solution to the baking soda solution. The hardness of water is defined in terms of its content of calcium and magnesium ions. Describe and apply the concepts of thermochemistry, the heat involved in chemical and physical changes 9. Question: EXPERIMENT 8: POST-LABORATORY Reactions In Aqueous Solution Double Displacement Reactions Post-Laboratory Questions DUE AFTER COMPLETING THE LAB Using The Solubility Rules, Predict The Solubility Of Each Of The Following Compounds In Water. A 0. 30 M perchloric acid (HClO4). Acid base reactions 1. Calcium Analysis by EDTA Titration One of the factors that establish the quality of a water supply is its degree of hardness. The way we measured how the solution has turned cloudy is by: A titration of pure vitamin C was performed by titrating a sample of vitamin C solution with 23. 3. Study. Experiment 6 - Elemental Analysis - Free download as Powerpoint Presentation (. Hold one pencil onto the bottle so about 2” (5 cm) of it extends beyond the opening of the bottle and keep it in place with the tape. Following earlier advances in method development , the authors inject salt solution (CoCl 2) at constant pump rates into a large reservoir of silicate solution. In small-scale chemistry, you often use plastic pipettes and microplates instead of large glass beakers, flasks, and test tubes. The precipitate produced by the reaction is insoluble, or slightly soluble, in the other aqueous product. If there was 20. Close to titration end point add titrant dropwise, until a faint pink color persists for 30 seconds. ppt / . 25 Quiz Thursday, 2/12 for 3rd and 9th period 7. Note that solubility is not always given as a molar value. Chemistry Books - www. Background: You will combine two water solutions, each containing positive and negative ions. Since HCl decomposes salts of weaker acids. Ionic compounds may be precipitated from aqueous solutions by mixing separate solutions containing the cation and anion of the ionic compound. Write balanced molecular equation, complete ionic equation, and a net ionic equation for each precipitation reaction. pptx), PDF File (. The only difference is that, in the addition of reactions 1&2, there was a hydroxide ion on both sides of the equation that was cancelled out (since I was asked for the net ionic equations for each reaction). 4. Examples of oxidation reduction (redox) reactions, oxidizing and reducing agents, and common types of redox reactions. Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not There are five types of chemical reactions: 1. Conclusion: Reaction of displacement of copper by zinc in copper sulphate solution is exothermic, as heat is released upon reacting. mixture consisting of a very dilute solution of Ag+ and Cl– ions in equilibrium with undissolved silver chloride: PbS, 7 × 10–29 . Dr. 12A: Practical Applications of Redox Reactions (Research Report would replace the following solution in Set A below: 2 ´ 0. Solid A dissolves in water to form a conducting solution. If you're seeing this message, it means we're Volumetric methods may be based on acid/base reactions. The term “proof” is defined as twice the percent by volume of pure ethanol in solution. Week 1: 9/29 and 10/1 . Or, add RNAase directly to lysis buffer with a final concentration of 1 mg ml -1 . containers can lead to injury from unexpected chemical reactions. Identify the ions present in various aqueous solutions. You may wonder why this is something that’s important, and frankly, that’s not a bad question. Sour 2. Acids, Bases, and Solutions ANSWER KEY Acids, Bases, and Solutions Describing Acids and Bases Review and Reinforce 1. 17. 1. In this lab we are going to see a precipitation reaction. b. Chapter 6 32 experiment, you should be quantitative; for example, if you find that the %RSD of your determinations of calcium in the gravimetric calcium experiment is 0. You will also see the effect of ions WEST LOS ANGELES COLLEGE CHEMISTRY 60 : INTRODUCTION TO GENERAL CHEMISTRY MAR 29 8 Modern Atomic Theory Chapter 11 9 Th 4/21 Exp 10 Precipitation reactions. Experiment 3 Gravimetric Determination of Nickel 5 . The following content was provided by Scott A. The breaking of chemical bonds requires the addition of energy, usually in the form of heat. clean the reaction beaker, as you'll be pouring the precipitate (solid) right 29. This reaction produces metallic copper, which is seen precipitating as a finely divided red powder. Key Takeaways Key Points. Basic format described on the mole-to-mole ratios in any report precipitation reaction: if a recently published within the yield. Sodium hypochlorite, NaClO, is a very pale yellow liquid. the report sheets in the lab manual and are due no later than a week after the lab is done. In this experiment, you will try to identify 12 different chemical. 810 grams Answers to SelectedTextbook Questions Chapter 1 There are no in‐chapter answers necessary for this chapter. Includes, but is not limited to, the reactions of elements with Oxygen and Sulfur; the reaction Although ozone (O 3) has been used as a disinfectant of water for over eight decades (Lawrence and Cappelli, 1977), relatively little is known about its chemistry as an oxidizing agent of organic and inorganic solutes in aqueous solution. Chapter 18 Precipitation and Complexation Equilibria SY 4/12/11 18–4 Example problem, continued Step 2. Then, add a few drops of 95% dimethylglyoxime precipitation [1] over two laboratory periods, the analysis of the waters of hydration in aluminum sulfate has been substituted. 80 g of lead nitrate in water and make up the solution to 10 mL. In chemistry, a precipitate is an insoluble solid that emerges from a liquid solution. Their simple but innovative idea was to perform this experiment under quasi-2D conditions in a horizontal Hele-Shaw cell, which consists of two closely spaced, parallel plates with a Let's find out the molarity or concentration of sulfuric acid solution from the given and observed data (molarity and observed volume of sodium hydroxide). I can apply my understanding of polarity to predict solution formation. Could this account for the difference, or does it have no role in the enthalpy of reaction, given that it is a spectator ion? Answers in your notes but keep this sheet for reference. Have students make 10. Experiment 4 Sodium Acid Salt of Heptaoxodiphosphoric Acid 6 web. Need to report the video? We'll start with the basics of what precipitation reactions are and then go through three examples together step by step. Some of the grade will be based on quality of results, for example successful identification of an unknown, or high yield, or high product purity. Precipitation continues until the reaction quotient equals the solubility product. The process of adding standard solution until the reaction is just complete is termed as titration and the substance to be determined is said to be titrated. PDF Document Bellow will provide you all associated to 17 precipitation reactions lab wooksheet! answers guide. 0 mL of a 0. Arrhenius 2. 0 mL each of 30%, 40%, 50%, 60%, 70%, 80%, and 90% antifreeze solutions, recording the mass of each solution, labeling according to its percentage, and saving for the next experiment. 14 M stock solution. pdf), Text File (. On this page you can read or download grade 12 prescribed experiment 2 acid base reactions in PDF format. Determine the moles for ammonium iodide in 5. 5, One way to test the salinity of a water sample is to add a few drops of silver nitrate solution with a known concentration. The lowest prestudy and lab report grades are dropped. 1 PDT or photodynamic therapy requires a photosensitizer, light and oxygen. 0 mL of 0. 5 mL - 2 mL of DI water dropwise with good mixing, until the solution becomes cloudy. Like acid-base reactions, redox reactions are a matched set -- you don't have an oxidation reaction without a leaving the more water-soluble compounds behind in the aqueous solution. The molarity of the solution is: 2. . For example, during three rounds of the experiment, the amount of NaOH needed to react with sulfuric acid is 12 ml, 13 ml, and 12. - Homework Answers (PDF) - Sample problem answers - Thermochemistry Worksheet 1 - Thermochemistry Worksheet 2 - Worksheet 1 & 2 Answers (PDF) - Additional Sample Problems (PDF) Here are the additional practice problems we didn't get to. Although the present experiment deals with an acid-base reaction, potentiometric titrations can alsobe used with redox reactions, precipitation reactions and complex formation reactions, as well astitrations in non-aqueous systems. A solution of hydrogen peroxide is 30. mL . Before beginning with chemical reactions, it is important to know about physical and chemical changes. You see, the six types of reaction are only one of many different ways to categorize chemical reactions. (4) Write the correct rate law expression for the reaction, in terms of crystal violet only (omit OH–). Agglutination Reactions 5. Issuu is a digital publishing platform that makes it simple to publish magazines, catalogs, newspapers, books, and more online. 45. c. Use a new report sheet to repeat work and be sure to staple any new calculation checks along with the original unknown report sheet to it! Report sheets turned in after deadline dates listed later in the syllabus will face a penalty for late work as noted in the table above. Doesn’t react with metals 5. After reaching the peak temperature, the new solution starts to cool down, as it loses its heat to the surrounding environment. Answers will vary. , and is maintained in a database by the ISS Program Science Office. Calculate standard chemical parameters including density, specific heat, heat of solution, gas laws, solution concentrations, and molar masses 10. Advanced Placement Chemistry is a rigorous second-year chemistry course for students who have completed Chemistry I at the honors level. general remarks. Stir. D. Chill the Erle nmeyer flask in an ice bath with occasional swirling to cause precipitation of the product. PRECIPITATION REACTIONS AND WRITING CHEMICAL EQUATIONS EXPERIMENT 11 NOTE: You do not need to do a regular lab report and coversheet. Lange's Handbook of Chemistry We believe this edition of Lange to be a close-at-hand, bookshelf necessity for science students, chemists, chemical engineers, and for others whose sphere of interest intersects with that of chemistry. Before we practice calorimetry problems involving chemical reactions, consider a simpler example that illustrates the core idea behind calorimetry. 43 M Iodine solution. However the subject guide does list eleven Solubility Equilibrium . com has a library of 550,000 questions and answers Qualitative analysis is used to identify and separate cations and anions in a sample substance. If a precipitate forms, SO 4 2-is in excess and Ba2+ is the limiting reagent. Complement Fixation Reactions 6. The actual extract solution from the paint chip samples contains lead acetate rather than lead nitrate. This is a HUGE question to answer completely! One answer is 'because they result in a negative change in free energy, delta-G. Precipitation reactions can help determine the presence of various ions in solution. to standardize a sodium hydroxide solution via titration using a buret and stirrer, and conduct a weak acid-strong base titrate to determine the concentration of a store brand vinegar solution to 3 correct significant digits (as described in Experimental Chemistry, by James Hall, Experiment 29) 3. The Dreaded Nine-bottle Problem Almost all salts [a salt is an ionic compound] exist in water solutions as separated ions. If you don't see any interesting for you, use our search form on bottom ↓ . The Color Of The Stareh. 12 Complex Is B. This experiment is completed in one laboratory period and a microwave oven can be used to speed up the drying process [1,2]. a. In this way, the concentration The best kind of effect is the change of color of the solution or formation of the colored precipitate. 5 × 10–3 M. Because both components of each compound change partners, such reactions are sometimes called double-displacement reactions. Kinetics Experiment Solution 1. Combine solutions and identify the reactions that form precipitates. 2Classifying Chemical Reactions By the end of this section, you will be able to: • Define three common types of chemical reactions (precipitation, acid-base, and oxidation-reduction) • Classify chemical reactions as one of these three types given appropriate descriptions or chemical equations • Identify common acids and bases 3. Name: Cooper Chung Date: 10/20/11 Lab Partner: Jessie experiment 10 precipitation reactions answers. To make up 10 mL of lead nitrate solution that is 50 mg/mL with respect to lead, we can dissolve 0. Enzyme-Linked Immunosorbent Assay 9. Immunodiffusion Test 3. d. Introduction: The goal of this experiment is to determine the cations present in a solution or mixture of solutions. in your report sheet, add 4-5 drops of each of the two specified reactants and mix well. On the other hand, if you want to compare reactions that appear to be instantaneous at room temperature, you'll need Another way to separate the precipitate from the solution is using a centrifuge. The functionality of every portable electronic device you own, whether it be your laptop, Ipod, or cell phone, is made possible by electrochemical reactions. edu PRECIPITATION. 3 The tumour must be located in a place that can be subjected to light. 0 mL of 2. The process of qualitative analysis assumes that each chemical test for an ion is unique to that ion. According to many college professors, AP Chemistry is equivalent to eight credits (two semesters) of a college honors chemistry course intended for chemistry majors. e. 29. Use solubility to calculate the ion concentrations at equilibrium. 0% H2O2 by mass and has a density of 1. Combination/Synthesis Reactions: two or more substances combine to form a new compound (A+X->AX). Description Sodium thiosulfate solution is reacted with acid, a precipitate of sulfur forms. 022 grams of sodium benzoate in 189. The solubility is measured in terms of concentration of an ion that is present in a smaller ratio in solution. REVIEW QUESTIONS 1. Introduction: You will study double displacement reactions using a small-scale method and predict the products of double displacement reactions. 50 M hydrobromic acid (HBr) to 500. Late reports will not be accepted (no kidding!!!). Introduction I must produce a piece of coursework investigating the rate of reaction, and the effect different changes have on them. The Kinetics Of The Reaction H₂O₂ + 2HI = 2H₂O +2I in Aqueous Solution Yufei Chang • Group X5. For instance, several chemists might get different answers when measuring a piece of rope or rubber band if they do not know what the tension is supposed to be. Learn chemistry lab 5 experiment with free interactive flashcards. To calculate potassium permanganate solution concentration use EBAS - stoichiometry calculator. Testing for excess SO 4 2-. Blue 9. chemical reactions. identify the products formed in these reactions. 5 Jun 2019 Precipitation reactions occur when cations and anions in aqueous solution combine to form an insoluble ionic solid called a precipitate. Report 2013 Chemistry GA 3: Examination GENERAL COMMENTS The 2013 Chemistry examination, the first two-and-a-half hour end-of-year examination, was based on the key knowledge and key skills for both Units 3 and 4. 5. 3: Predicting Precipitation Reactions 8 (Sample Response) 29 Appendix 1. Precipitation Reactions 2. Neutralization Reactions 7. Of the various methods of expressing solution concentration the most convenient for general laboratory use is molarity, which is defined: Moles of solute n solute the report sheets in the lab manual and are due no later than a week after the lab is done. Chemistry is the branch of science pertaining to the study of the composition, structure, properties, and reactions of matter, especially those of atomic and molecular systems. One way to prepare a standard solution is to dissolve an accurately massed amount of the substance and dilute it to a measured volume (like we did with the MnO 4-solution in Expt. 0167 g CaF 1 mol CaF 1 mol Ca W/S(activity): Identifying Types of Chemical Reactions — see GC to make corrections to Analysis & Conclusion. There are no specific experiments or practicals that all students must perform. Calculate the enthalpy change (heat of solution) for the reaction in kJ mol-1 of solute. This chemistry video tutorial explains how to balance and predict the products of precipitation reaction in addition to writing the net ionic equation. Reminders: Presentation Day, Wednesday, Feb. In this enzyme experiment, you will get to see enzymes in action and an experiment challenge for you to do on your own. Predicting and determining the products using the reactivity series. Well-prepared students were able to attempt, and generally complete, In this lab you'll be studying reactions between acids and bases. Easily share your publications and get them in front of Issuu’s Much was learned in this experiment. Procedures: 1. Read 14 answers by scientists with 3 recommendations from their colleagues to the question asked by Steven J Granger on Jan 24, 2014 How does Trichloroacetic acid (TCA) extract phosphate from Have them save this solution for the next experiment. Often the precipitate emerges as a suspension. Abstract The aim of this experiment is to find out the rate constant and the energy of What volume of a 0. Deniz Korkmaz Introduction Titration is a process by which the concentration of an unknown substance in solution is determined by adding measured amounts of a standard solution that reacts with the unknown. Method: In trial run 1 we used a solution called sodium thiosulphate to measure how long it takes to turn cloudy when you mix a certain amount of water and acid to it. In a redox reaction, two half-reactions occur; one reactant gives up electrons (undergoes oxidation) and another Experiment #8: Limiting Reactant Abstract In chemical reactions, the significance of knowing the limiting reactant is high. Litmus is a good indicator for an acid-base titration, because it changes color at a pH of around 6. The amount recovered divided by the theoretical yield gives a percent yield (% yield) or actual yield. Unknown Salts Project Page 6 of 13 Procedure Notes: • Use as little of materials as possible. They will also use a "control" solution to confirm that the sample is not contaminated. the theoretical yield and to calculate the percent yield. 2) Individual Lab Scores: Most experiment will require completion of a lab report and answers to some questions. 5 M Ba2+ ion (from 0. 0 mL of vitamin C in the flask, what was the initial At that time ask any questions you have about carrying out the calculations, doing the report, etc. They will check for the presence of the chloride ion, which forms a white precipitate in the presence of the silver ion. #1. Laboratory Manual The laboratory manual should be brought to class the day before and the day of the laboratory experiment. 35 mL of a 0. precipitation: the process of an insoluble salt forming from its aqueous ions and falling out of solution Instead, all ions remain in solution and no reaction occurs. III. Hypochlorite, ClO-(aq), is the bleaching agent in bleach. Two important uses of precipitation reactions are to isolate metals that have SIC1002 Inorganic Chemistry I Practical Manual . Chemists classify chemical reactions in a number of ways: by type of product, by types of reactants, by reaction outcome, and by reaction mechanism. 350 M HCl? reactions and test Le Châtelier’s principle by manipulating concentration and temperature of the reactions. Contents. Add 2 drops of 0. This is not an example of the work produced by our Essay Writing Service. (5) Calculate the half-life of the reaction (in minutes) using the pseudo rate constant, k 1, and the appropriate half-life equation. AP Chemistry. ' This may be as a result of the reaction being exothermic, so the products are more stable than the reactants, or could be a result of an increase in entropy (products more disordered than the reactants), or both of these. Precipitation reactions C. Liquid butane (C4H10 (l)) is used as a fuel to ignite a lighter. The benzoic acid will then be isolated using aqueous hydrochloric acid to turn the solution acidic which will make the benzoic acid precipitate. Counter Current Immunoelectroptioresis Test 4. 5°C. 5 ml, respectively. EXPERIMENT 10: DOUBLE REPLACEMENT REACTIONS . The pencils will be the legs of the rocket. 125 M solution is concentrated by evaporation to a reduced final volume of 100. 328 M . The formation of gas (some bulbs inside the solution) can be a possible option as a visual effect. The assigned topics must be done by the due dates for full credit. Electrochemistry is the study of the relationships between chemical reactions and electricity. Chemical reactions are all around us, from the metabolism of food in our body to how the light we get from the sun is the results of chemical reactions. Check the weekly class syllabus for lab dates. Always begin with a small amount of solid (perhaps a tiny sample on the tip of a scoopula). c) Iodine with sodium hydroxide, NaOH solution B. If no precipitate forms, scratching the side of the flask with a glass stirring rod may help initiate crystallizatio filtration apparatus as shown in the figure to the right. Calculate the original volume. The temperature of the water rose to 27. Student Solution Manual The Student Solution Manual is intended to be left at home. b) Systematically combine solutions and identify the reactions that form precipitates and gases. (S N Soluble, 1-insoluble D) Pb(NO,), B) Al(OH),一 Predict Whether A Precipitation Reaction chemistry. 100 M chloric acid (HClO3) with 225 mL of 0. Copper metal is placed in a solution of This is a collection of worked general chemistry and introductory chemistry problems, listed in alphabetical order. If no reaction is visible after about 10 min, give up — we'll call that unreactive. Single replacement reactions Definition of single replacement (or single displacement) reactions. Isolating the solution and adding a small amount of Na 2 CrO 4 solution to it will produce a bright yellow precipitate of PbCrO 4 if Pb 2+ was in the original sample (Figure 17. A precipitation reaction is said to have occurred if the solution turns cloudy. Only add more if needed. As the solutions of sodium chloride and silver nitrate mix, a precipitate of silver chloride forms, and sodium nitrate is left in solution. Assuming the change in volume when the sodium benzoate is added is not significant, use the Henderson-Hasselbalch equation to estimate the pH of the solution. Since protons cannot exist in solution as independent species, the tendency of an acid or a base to donate or accept a proton (as in Eq 1) cannot be measured for individual acid or base species separately; the best we can do is compare two diDerent acid-base systems, and determine the extent until all the solid dissolves (add a little more ethanol if the entire solid is not in solution just as the solution begins to gently boil). About 30 mL of 3 M HCl was added to the solution containing the 2-naphthoxide. B is not soluble in water. Experiment 2 1 Chemistry 112 Laboratory Experiment 2: Investigating Periodic Trends- Halogens and Alkaline Earths Introduction The beauty of the periodic table is its elegant way of listing elements to assist our prediction of Featured Kit Chemistry Magic Tricks Kit With this cool experiment kit, you’ll be able to make color-changing solutions and even turn water into a solid instantly! The 12 chemistry tricks in this kit will amaze your friends plus teach about the science of pH, acids and bases, density, chromatography, and polymers. The six tests are: (1) Ninhydrin Test (2) Biuret Test (3) Xanthoproteic Test (4) Millon’s Test (5) Hopkins-Cole Test and (6) Nitroprusside Test. Some errors in the chemistry lab result from an unclear definition or expectation of what the experiment is supposed to record. Although often listed together with strong mineral acids (hydrochloric, nitric and sulfuric) phosphoric acid is relatively weak, with pK a1 =2. Lab: Chemical Reactions I Objectives x Understand qualitative tests for ions that are based on solubility x Learn that Na+, SO 4-and Na 2CO3 are water soluble x Recognize balanced chemical equations x Perform a qualitative experiment with aqueous solutions Introduction Many of us remember those tearful moments in the bath when soap got in our However, in a reaction to prepare a compound, you may get less than the theoretical yield, because of incomplete reactions or loss. Since an analysis does not distinguish between Ca2+ and Mg2+, and since most hardness is caused by Questions are presented throughout each experiment. Calculate the molarity of the base. Thus precipitation reactions are a subclass of exchange reactions that occur between ionic compounds when one of the products is insoluble. 0 mL. 0. Titration is a process of slowly adding one solution of a known concentration to a known volume of an unknown concentration until the reaction gets neutralized. These two precipitates will be collected using vacuum filtration. Determination of phosphoric acid concentration by alkalimetric titration. What would appear in solution if the Na 2 S 2 O 3 solution were omitted? 4. 64. 1 presents a summary of the volumetric methods commonly used for environmental analysis. Reactions of halogens with sodium hydroxide, NaOH solution 25 a) Chlorine with sodium hydroxide, NaOH solution b) Bromine with sodium hydroxide, NaOH solution. For each of the reactions indicated in your report sheet, add 4-5 drops of each of the two specified reactants and mix well. listed in the first row of the table in question 1 of your lab report. Examples of qualitative tests would include ion precipitation reactions (solubility tests) or chemical reactivity tests. Appendix 1. Experiment 3 a) Add a small scoop of baking soda, sodium bicarbonate, to a test tube and add water to height of about 1 centimeter. 0 mL of water to produce a new molarity of 0. Zinc in powder reacts faster as the total surface area is higher. From this information, you can find the concentration of the Ba(OH) 2 solution. In this lab you will use your knowledge of precipitation tables to predict precipitation reactions. 6). OBJECTIVES 1. With the 7 th Edition of Analytical Chemistry renowned chemists, Purnendu (Sandy) Dasgupta and Kevin Schug, both of the University of Texas Arlington, join the author team. Calcium fluoride dissolves to an extent of 0. The amount of time required in the two runs should agree within 20 seconds. I can collaboratively develop a detailed procedure for my experiment. Such physical processes are classified into two types: Heat of solution and Heat of dilution. Oxidation reduction reactions 1. If a precipitate forms, Ba2+ is in excess and SO 4 2-is the limiting reagent. Among the different areas of chemistry are biochemistry, electrochemistry, organic chemistry, and nuclear chemistry. What Are The Colors Of The Following Ions? K 2. Red 8. Before looking at what makes it an acid-base extraction, first experiment date(s): Experiment 43 - Spot Tests for Some Common Ions Goal: To observe distinguishing chemical tests for some common ions and use these tests to identify the ions in an unknown mixture. What happens in test for sulfur use of lead acetate, albumin and naoh? What is the name of the black precipitate formed when a few drops of lead acetate are dropped to the dilute sodium hydroxide solution? Heat up the solution to about 70°C. On this page you can read or download experiment 2 acid base reactions memorandum only in PDF format. c) In another test tube place the same amount of baking soda and dissolve as above. Question: REPORT SHEET EXPERIMENT Rates Of 29 Chemical Reactions I: A Clock Reaction A. 0500 M. 31. Calculate the concentrations of aqueous reactants and products using a chemical equation. Instead, all ions remain in solution and no reaction occurs. 2 g of sodium hydroxide pellets, NaOH (s), were dissolved in 100 mL of water at 25°C. Doesn’t react with carbonates 7. Instrument Limitations • Experiment should be handled carefully and slowly. All reactions will be performed in the 96-well plate. • Most precipitation reactions happen when a double displacement reaction takes place -that is the cations and anions of two ionic compounds change partners. It acts by oxidizing the "stain molecules" to less-coloured forms of the molecules. If the experiment failed, this is the place to explain why, in what way, and how Essay about Lab Observations of Chemical Changes 825 Words Oct 5, 2014 4 Pages Observations of Chemical Changes Purpose: The purpose of this experiment is to observe chemical changes in common consumer products to determine if the chemicals are basic, acidic, or remain neutral when mixed with other chemicals. Red blood cells placed in an isotonic solution will retain their normal size, that is they neither gain nor lose water by osmosis. , no reaction occurs], may combine to Find helpful Chemistry questions and answers on Chegg. Complete this lab sheet and answer all Analysis questions. Could this account for the difference, or does it have no role in the enthalpy of reaction, given that it is a spectator ion? Redox reactions, or oxidation-reduction reactions, have a number of similarities to acid-base reactions. Solution Stoichiometry Practice Problems Experiment 6 Chemical Reactions OUTCOMES After completing this experiment, the student should be able to: be familiar with a variety of reactions including precipitation, acid-base, gas forming, and oxidation-reduction reactions. Kim2, Young Mee Kim3;∗ 1 Department of Chemistry and Biology, Korea Science Academy of KAIST, 899 Danggam 3-dong, Busanjin-Gu, 614-822, Busan, Republic of Korea Tutorial 4 SOLUTION STOICHIOMETRY Solution stoichiometry calculations involve chemical reactions taking place in solution. Precipitation Reactions: A chemical reaction that involves the formation of an insoluble product (precipitate; reactions of ionic compounds in aqueous solution (water), the typical molecular . Page 2 of 7 EXPERIMENT 3: REACTIONS IN AQUEOUS SOLUTIONS (Read through this prior to beginning the pre−lab) This experiment corresponds to chapter 3 in your text) Introduction Chemical Reactions: Introduction to Reaction Types **Lab Notebook** Record observations for all of the chemical reactions carried out during the lab in your lab book. Classify chemical reactions 8. No makeups are given for missed exams, quizzes or lab Learning 5 basic categories of chemical reactions helps chemistry students with the essential skill of writing and balancing chemical equations—and boosts their ability to predict reaction products when only given reactants. The composition of solutions, types of chemical reactions, precipitation reactions, describing reactions in solution, Stoichiometry of precipitation reactions, acid-base reactions, oxidation-reduction reactions, balancing oxidation-reduction equations 118-156 2/4 Experiment 6: The Copper Lab Lab Handout 2/5 & 2/8 Chapter 13 Properties of Solutions: A standard solution is one in which the concentration is known accurately. The time taken for a certain amount of sulfur to form can be used to indicate the rate of the reaction. Dulchavsky, M. Grades will be posted on the web and updated weekly. In terms of calcium ion concentration, 2+ 2+ -422 22 0. The above reaction will produce a solid precipitate of and an aqueous solution of. credit since it reacts with water and so cannot be made into an aqueous solution. 0. The approximate pH of a solution is determined by removing a drop of the solution with a stirring rod and touching it to a piece of universal indicator paper. This suite includes the popular co-produced Nuffield Foundation and Royal Society of Chemistry ‘Practical chemistry’ series. Suppose we initially have a high-temperature substance, such as a hot piece of metal (M), and a low-temperature substance, such as cool water (W). Chemistry Small-Scale Laboratory Manual activities use the latest development in laboratory techniques—small-scale chemistry. The new edition focuses on more in-depth coverage of the principles and techniques of quantitative analysis and instrumental analysis (aka Analytical Chemistr A solution was made by dissolving 0. Question/Answer: stevieg asked on 03/22/07 - moles. !! When!the!exact!composition!of!a!mixture!is!known,!it!is!called!a!solution. Apart from the thermal energies resulting from the chemical reactions many physical processes including the ice melting or the vapour condensation is accompanied by the absorption or release of heat. (d) A solution prepared by diluting 15. When you add a hydrochloric acid (HCl) solution to a solution of sodium carbonate (Na 2 CO 3), the hydrogen ion in HCl switches places with one of the sodium ions in Na 2 CO 3 to produce sodium hydrogencarbonate, also known as sodium bicarbonate (baking soda), and sodium chloride (salt). Translate these sentences into a balanced chemical equation. CHAPTER 4: ANSWERS TO ASSIGNED PROBLEMS Hauser- General Chemistry I revised 10/14/08 4. Purpose In this experiment you will calculate the free-energy changes of reaction, G rxn, for a variety of possible precipitation reactions, then use your calculated values to predict whether a precipitate will View Notes - Chem 1251 Lab Report - Precipitation Reactions and Limiting Reagents from CHEM 1251 at University of North Carolina, Charlotte. This page looks at some typical reactions of diazonium ions, including examples of both substitution reactions and coupling reactions. 66 Determine the hydroxide ion concentration and the pH of the following strong base solutions. Concentration of a solution. This video contains plenty of notes Precipitation Reaction (lab exercise) Precipitation is one of the fundamental reaction types. You may also browse chemistry problems according to the type of problem. Introduction It had been a good year for the O’Keefe farm with just the right amount of sun In qualitative analysis, the ions in a mixture are separated by selective precipitation. A 100 or 150 ml beaker of boiling distilled water is used to heat solutions in test tubes. Still, when working with The following points highlight the nine important antigen-antibody reactions. Repeat steps 2-5 for other mixtures listed in your report sheet, making sure the temperate is kept within about a degree of that in the initial run. This technique is used when the solid particles are very small and dispersed in the solution. This is especially true for solid reagents where too much of a sample may mask precipitation reactions or hide solubility. Laboratory Notebook (Binder) - Rate of Reaction Between Calcium Carbonate and Hydrochloric Acid Plan: In my experiment I will measure the rate of reaction between calcium carbonate and hydrochloric acid. Explain the advantage that additional test reactions have on determining p and q as you did in this experiment. Key Terms. If no insoluble combination between anions and cations exist, no precipitate will form. Barium hydroxide solution is neutralized by adding hydrochloric acid (HCl (aq)). Experiment 17-Chemical Reactions Lab - Bakersfield College If the substance no longer had an aqueous solution after the double replacement, then the substance would be a precipitate. Precipitation Titration: Determination of Chloride by the Mohr Method by Dr. Students will learn about spectroscopes and how they are used to create and PDF | The aim of this study is to analyze and improve the experiment of the acid-base neutralization reaction described in science textbooks. Commercial solution calorimeters range from (a) simple, inexpensive models for student use to (b) expensive, more accurate models for industry and research. !!In principle,asolutioncanbeasolid for this reason direct conductance measurement are of little use unless the solution contains only the electrolyte to be determined or the concentrations of other ionic species in the solution are known. 9% NaCl (normal saline solution) and 5% glucose solutions are isotonic with body fluids. (e) A solution prepared by mixing 175 mL of 0. The time taken for a certain amount of sulfur to form is used to indicate the rate of the reaction. These tests were done to give students a better understanding of double replacement reactions. com. They are: 1. Reaction types A. are of vii Grade 12 C hemistry • Acknowledgements AC This document is based on a draft version of Grade 12 Chemistry: A Foundation for Implementation, which was released on the Manitoba Education website in fall 2004. Often a given reaction can be placed in two or even three categories, including gas-forming and precipitation reactions. Conductometric titrations, in which the species in the solution are converted to non-ionic for by neutralization, precipitation, etc. 5—close enough, as will be explained below. For most experiments performed this term you will turn in a report that, unlike CH227H, form an insoluble compound that leaves the solution as a solid precipitate. Unlike quantitative analysis, which seeks to determine the quantity or amount of sample, qualitative analysis is a descriptive form of analysis. ’ Solubility Product Constants, K sp. The effect of temperature on reaction rate Topic Rate of reaction. A precipitate is when two aqueous solutions are combined together to form a solid product through double replacement reactions. . STUDYING THE PROPERTIES OF OXIDES OF THE ELEMENTS IN PERIOD 3 I. To perform a precipitation, add the indicated reagent to your test tube and mix thoroughly. quotients calculated from experimental data to tell whether a solid will precipitate in a reaction under specific  EXPERIMENT 3: REACTIONS IN AQUEOUS SOLUTIONS (Read through period, your lab instructor lectured on the topic of reactions in aqueous solution with examples of the correct There are three types of metathesis reactions— precipitation reactions, . Insoluble Chlorides All salts formed in this experiment are Ag+ Pb2+ Hg22+ said to be INSOLUBLE and AgCl PbCl2 Hg2Cl2 form precipitates when mixing moderately concentrated solutions of the metal ion with chloride ions. Examine the lists of solutions you will be using for this experiment. Note that if it a graphing calculator, I reserve the right to clear it’s The only difference is that, in the addition of reactions 1&2, there was a hydroxide ion on both sides of the equation that was cancelled out (since I was asked for the net ionic equations for each reaction). 20 and pK a3 =12. 5 M BaCl 2) to the other 50 mL of solution in Beaker II. The effect of temperature on the rate of reaction can be investigated. The increase in kinetic energy that comes with higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions. Some candidates did describe repeating the experiment without the So, for subsequent reactions, for example, to digest plasmid DNA, add 1-5 μl (1 mg ml-1) RNAase to the digestion solution to completely remove RNA. All chemical reactions cannot be considered as titrations. The Reaction of Iron with Copper (II) Sulfate Introduction In this experiment we will use stoichiometric principles to deduce the appropriate equation for the reaction between metallic iron and a solution of copper (II) sulfate. Oxidation number 2. 6455 jan 29 experiment 10 lab: single phase solid, cooking, chemical equations for this experiment. Taking into consideration the value of data presented, the manual is a great find for readers wanting to introduce an organized system in conducting laboratory experiments. 9. Answers to all pre-lab questions (if pre-lab questions exist). While the solution is still on the hot plate, add 0. 8. There are six tests for the detection of functional groups in amino acids and proteins. e. Add 25 mL of ice water to the reaction mixture. (ii) The titration method was well known by some candidates and descriptions often included the three required marking points. 2%, you should say so in the conclusion, and point out that this is pretty good precision. Ask any chemistry question and an expert will answer it in as little as 30 minutes. Bitter 3. McGraw-Hill Dictionary of Chemistry . This experiment serves as an introduction to the area of synthetic chemistry – and These complex cations crystallize from solution . This type Experiment 9 Electrochemistry I – Galvanic Cell Introduction: Chemical reactions involving the transfer of electrons from one reactant to another are called oxidation-reduction reactions or redox reactions. The emergence of the insoluble solid from solution is called precipitation. Determine the volume of stock solution required to make 47 mL of a 5 mM solution starting with a 0. 0 mL of a solution of NaOH is diluted by adding 250. Qualitative analysis is a method used for identification of ions or compounds in a sample. Radioimmunoassay 8. Hands-on practical activities or ideas for front of class demonstrations Hands-on practical activities or ideas for Experiment 7 Fall 2009 3 about 3 minutes, warm the tube(s) to 40-50°C and record the time required for precipitation. As such, this experiment uses qualitative analysis (a means for determining the chemical composition of an unknown substance by systematically reacting the unknown substance with a number of different reagents) to identify the cations present, by the reactions produced. 25 grams of pulverized copper sulfate are dissolved in the 85 ml of cold 6 N (~10%) ammonium hydroxide solution. ung. In many cases, qualitative analysis will also involve the separation of ions or compounds in a mixture. Laboratory Activity. In an experiment, 1. Some of you may have already met solubility in lecture and have seen some of the 'Guidelines' that a chemist has “Reactions in Aqueous Solutions” Illinois State University, Normal, Illinois. In addition, you are encouraged to complete the report as soon after laboratory as possible, as this is 8. Lowry-Brønsted 3. Students use it as a resource when completing their homework. $Fus$ $ CHEM$1220$ $ 1$ $ CHEMISTRY*1220!! CHAPTER17(PRACTICEEXAM$ All!questions!listed!below!are!problems!takenfrom!oldChemistry!123!exams!givenhereat!TheOhio State! 5 HOS 3430C Nutrition of Horticultural Crops Report of Lab 3 (100 points) September 27, 2016 Report due: September 29, 2016 Objective: Understand the functions of nutrient elements essential for plant growth and development. Choose from 500 different sets of chemistry lab 5 experiment flashcards on Quizlet. Table 16. Have noticed, 2010 chemistry chem 127 at our ebook. Connect, an online homework set is required and is worth an exam grade. Aqueous Solution: Definition, Reaction & Example Precipitation and acid/base reactions can involve the use of aqueous solutions. Directions for Writing a Laboratory Report Identification of an Unknown Cation (to be concluded in the next lab period) HAND OUT 2 Identification of an Unknown Cation (continued from previous week HAND OUT 3 Rates of Chemical Reactions I: A Clock Reaction 29 331 4 Quiz 1 The Chemistry of Oxygen: Basic and Acidic Oxides and the Periodic Table 18 Theme-based Project Learning: Design and Application of Convergent Science Experiments Man-Seog Chun1, Kwang Il Kang1, Young H. Unless notified otherwise lab reports should be completed by the following lab period. Stick one end of the tape to the middle of the bottle but don’t wrap it around the bottle, yet. A decomposition reaction is a chemical reaction in which some chemical bonds in a compound are broken and simpler substances are formed. The common ion effect can also play a role in precipitation reactions. Two test reactions are the minimum required to obtain values of p and q in this experiment. Identify a redox reaction as well as what atoms are being oxidized and reduced in the reaction. A solution of lead (II) nitrate is mixed with a solution of sodium iodide. REACTIONS Chapter 17 Part 2 2. Lewis B. This in fact is how decaffeineated tea and coffee are sometimes made. txt) or view presentation slides online. The fast spinning of the tube in a centrifuge (see picture below) causing the solid gathers at the bottom of the tube due to higher density and gravity force. Include units in your answer; be sure to use standard abbreviations such as those that appear in the question. Titration of the phosphoric acid H 3 PO 4 is an interesting case. C dissolves in water to form a nonconducting solution. In this exercise, you will observe and use chemical equations to describe a precipitation reaction, and when antigens and antibodies meet in solution - there is an optimal concentration of each where precipitation may be seen by the naked eye - if antibodies and antigens match, precipitate will form - if concentration of either is too low, antibody-antigen rxns will still occur, but precipitate will not be visible unaided The report for this exercise consists of completing the attached Report pages (pp. Rate of Reaction - Sodium Thiosulphate and Hydrochloric Acid Aim Investigation, to find out how the rate of reaction between Sodium Thiosulphate and Hydrochloric acid is affected by changing the concentration. Experiment 1 Calibration of a 25-mL Pipette 1 . 0167 g per L of solution. write balanced chemical equations and net ionic equations. An acid-base extraction, this week's experiment, is a modification of the second case above; that is, it is a solvent-solvent extraction. Explore over four hundred exciting practical experiments that demonstrate chemical concepts and processes. Report your answer to two digits past the decimal point. Precipitation is a process in which a solute separates from a supersaturated solution. com has a library of 550,000 questions and answers for covering your Experiments and illustrations of chemical reactions are presented. 228 M benzoic acid. One of the more obvious things seen is the inefficiency of small-scale synthesis reactions. Identify 11/29 -12/6 9 - Liquids & Solids 12/7 - 12/14 10 - Solutions Types of Chemical Reactions and Solution Stoichiometry (Chapter 4) (2 weeks) I. The answers are given (at the end) but they are not worked out. The purpose of this experiment is to use stoichiometry to predict how much of a product will be made in a precipitation reaction, to measure the reactants and products of the reaction correctly, to figure out the actual yield vs. Repeat the experiment, using as a reference the reacted solution instead of distilled water. The problems in the neutralization reaction of NaOH A solution whose concentration is known, is called a standard solution. You can view samples of our professional work here. However, we’re really only interested in the lead cation concentration. 5 x 11 format paper and handed in to the instructor on week after the experiment. For many solids dissolved in liquid water, the solubility increases with temperature. All of our content has been audited for health and safety in partnership with CLEAPSS. Swirl the . Produces carbon dioxide 6. Answer Key Precipitation Lab Purpose: 1. Synthesis description for preparation of TETRAAMMINECOPPER(II) SULFATE. The precipitation of CaCO 3, formed by mixing equimolar solutions of Na 2 CO 3 and CaCl 2 at different dilutions in aqueous solution, has been studied at 25°C. This week, we are talking enzymes. chem. Solubility is the ability of a substance to dissolve in water. 5 You are presented with three white solids, A, B, and C, which are glucose (a sugar substance), NaOH, and AgBr. Add hydrochloric acid. Induction periods were determined as functions of the initial supersaturation by different methods (visually, turbidimetrically and conductometrically) for the “pure” system and in the presence of Mg 2+, Mn 2+, Br-and NO-3 as trace Now that you understand chemical reactions, it’s time to start classifying them into smaller groups. In this experiment, you will monitor conductivity during the reaction between sulfuric acid, H 2 SO 4, and barium hydroxide, Ba(OH) 2, in order to determine the equivalence point. Included are printable pdf chemistry worksheets so you can practice problems and then check your answers. Titrate adding small volumes of titrant and waiting each time till the solution decolorizes. About 20 mL of acid was added to the benzoate solution to pass the endpoint of the titration. Fundamental oxidation/reduction reactions occur inside the batteries of these devices. edu ) The independent behavior of each type of ion in solution was illustrated in Chemical Bonding by means of precipitation reactions. REPORT: The lab report should be typed or hand written legibly on white 8. Corrosive to magnesium, zinc, and iron; eats them away and produces bubbles of hydrogen gas 4. Welcome to The Lab Report sponsored by Apologia Science. the 50 mL of solution in Beaker I. On the other hand, solubility equilibrium refers to the equilibrium between the dissolved salt (ions) The benzoic acid will be extracted by adding sodium hydroxide to the dichloromethane solution and using the process of separation. If you have come straight to this page from a search engine and want to know about the preparation of the diazonium ions, you will find a link at the bottom of the page. No makeups are given for missed exams, quizzes or lab Protein precipitation testing using albumin solution reacted with hcl ethanol copper sulphate and ammonium sulphate solutions. The 2-naphthol took much more than the estimated amount of acid to complete the precipitation. This trivia quiz is based on the titration problem of acids and bases that we learned and had some practice in the lab this week. This post contains affiliate links. A gas reaction Lab #6 - Precipitation Reactions This week's lab focuses on one of the more challenging concepts for new chemistry students: predicting the products of a double replacement reaction. 2 = – slope for zero and first order reactions and k 1 or k 2 = + slope for second order reactions). 0 mL and a molarity of 0. More often than not, these reactions will produce a precipitate; a solid substance that forms when two aqueous solutions are combined. A saturated solution is in a state of dynamic equilibrium between the dissolved, dissociated, ionic compound and the undissolved solid. pdf Lab Report Precipitate Lab Answers Reaction in Aqueous Solution Answers Experiment 17 Precipitation Reactions CHEMICAL PRECIPITATION REACTIONS - ANSWERS Depending on the year level you may or may not include the balanced chemical equations. Answer on separate sheet of paper. precipitation reactions, complexation reactions and redox reactions. Enthalpy of Solution (Heat of Solution) Example. Timing 60 min. Fundamentally, redox reactions are a family of reactions that are concerned with the transfer of electrons between species. I can explain why a solution forms in terms of polarity and solubility. 101science. Redox Titration of Bleach Key Concepts. Read this article to learn about the qualitative and quantitative tests for amino acids and proteins. 30. Which one requires the greatest volume of base to change the colour of the indicator? (A) Citric acid (B) Acetic acid (C) Sulfuric acid (D) Hydrochloric acid . Sodium thiosulfate solution is reacted with acid – a sulfur precipitate forms. Solubility product constants are used to describe saturated solutions of ionic compounds of relatively low solubility. 6. Answer: 1. The formation of colorless (white) precipitate is a little more difficult to detect. The rate of the reaction is the speed that the reaction takes place so by measuring the rate I will measure the amount of time the reaction takes. wisc. In order to increase the percent yield of product, increasing the limiting reactant, possibly, is the most effective. 11 g/cm3. EXPERIMENT 10: Precipitation Reactions Metathesis Reactions in Aqueous Solutions (Double Displacement Reactions) Purpose – a) Identify the ions present in various aqueous solutions. Transfer your filtrate to the cleaned out 250-mL reaction beaker. Writing laboratory 12 solution guide 1. Additionally, please answer the. 8 In a research report a student wrote, ‘ Acids are compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution. solution. 291 M solution of NaOH is required to reach the equivalence point in a titration against 25. When solutions of different salts are mixed, the ionic species present may remain in solution as separate entities [i. This control solution will not produce a precipitate. Selective precipitation involves the addition of a carefully selected reagent to an aqueous mixture of ions, resulting in the precipitation of one or more of the ions, while leaving the rest in solution. 3 ) Precipitation reactions : ( chemed. Disclaimer: This work has been submitted by a student. Reaction of oxides of Period 3 elements with water 29 II. PLEASE HELP! Thus precipitation reactions are a subclass of exchange reactions that occur between ionic compounds when one of the products is insoluble. In Part II you will work independently to carry out each of the reactions in one clean “spot plate” and note the observations. The substance used to prepare a standard solution is called the primary standard. 11 "The Separation of Metal Ions from Group 1 Using Qualitative Analysis"). 1 mol/L solutions of . The rate-limiting step in the 2. You also use small amount of chemicals in reactions. Since indicators react with the solution being measured, they should be used in moderation—only a few drops if possible. Page Guideline and Marking Scheme for Practical Report i . Name: Jovan Tucker Date: 29 September 2014 Class: Chemistry 111 (Online) Experiment 4: Ionic Reactions Purpose: To study the nature of ionic reactions. ! 151! Chapter9:!SolutionsandSolutionReactions. The Chem21labs. 15, pK a2 =7. To download free lab 7 double replacement How do write a hypothesis for a Precipitation Reaction Experiment? I have a practical report due in soon, and I don't know how to put a hypothesis about precipitation reactions. compared to the volume of solution. Precipitation Reactions • When soluble reactants combine to form a solid precipitate the reaction is called a precipitation reaction. Quantitative Spectroscope and Visible Light In this experiment, students will learn about light and how each light source creates its own unique spectra. Preliminary Experiments 1. 120. Solid zinc sulfide reacts with oxygen in the air. It is important that you try to answer each question as it appears in the manual, as it will help you understand the experiment as you do it. Science Experiment; Acid-Base Titration Lab Study. A solubility table can be used to predict precipitation reactions. Materials: “Fall 2011 General Chemistry I Laboratory Manual” ($8, available at CopyX, to the west of Jimmy Jones on Lincoln Avenue) Department-approved laboratory goggles A scientific calculator (one that can express scientific notations) is required. In acid-base titration, the neutralization point occurs at a pH of 7. Concentration of a solution is defined as the amount of a solute present in a definite volume of the solvent. 35. Apart from the ten hours for the Individual Scientific Investigation and the ten hours for the Group 4 project, teachers are free to devise their own practical programme to cover the remaining 20 hours (SL) or 40 hours (HL) of the allocated time for practical activities. Precipitates can form when two soluble salts react in solution to form one or more insoluble products. Commercially available solutions of bleach contain sodium hypochlorite, NaClO(aq). Undefined Experiment. Calculate molarity of a solution and concentration or volume for a dilution of a stock solution. M x A y (s) --> x M y+ (aq) + y A x-(aq) When hydrochloric acid reacts with any carbonates/hydrogen carbonates the products formed are metal chloride , water and carbon dioxide. A reagent can be added to a solution of ions to allow one ion to selectively precipitate out of solution. , Ph. Thus, a solution that is 95% (by volume ethanol is 190 proof. To write balanced equations and net ionic equations for precipitation reactions. report for experiment 29 reactions in solution i precipitation answers

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