Experiment 2 Prelaboratory Assignment 4. Identification of unknown. Obtain an unknown for Part A from your laboratory instructor. Repeat the three tests with the reagents in Parts A.1, 2, and 3 on your unknown. On the basis of the data from the "known” solutions (collected and sum- marized in the Report Sheet matrix) and that of your unknown solution, identify the compound in your unknown solution. Identification of a Compound: Chemical Properties Disposal: Discard the test solutions in the Waste Salts container. Date Lab Sec. Name Desk No. CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with deionized water. Discard each rinse in the Waste Salts container. 1. Experimental Procedure, Part A. a. What is the criterion for clean glassware? B. Chemical Properties of Unknown Compounds b. What is the size and volume of a "small, clean test tube"? 7a1 The design of the experiment in Part B is similar to that of Part A. Therefore, 15 clean test tubes or a clean 24-well plate is necessary. 1. Preparation of solutions. On the reagent shelf are five solutions labeled 1 through 5, each containing a different compound. Use small clean test tubes or the well plate as your testing laboratory. About 1 mL of each test solution is necessary for analysis. 2. Preparation of reagents. Also on the reagent shelf are three reagents labeled A, B, and C. Use a dropper pipet (or dropper bottle) or a Beral pipet to deliver reagents A through C to the solutions. 3. Testing the solutions a. Test each of the five solutions with drops (and then excess drops) of reagent A. If, after adding several drops, you observe a chemical change, add 5-10 drops more to see if there are additional changes. Observe closely and describe any evidence of chemical change; record your observations. b. With a fresh set of solutions 1-5 in clean test tubes (or wells), test each with reagent B. Repeat with reagent C. 4. Identification of unknown. An unknown solution will be issued that is one of the five solutions from Part B.1. On the basis of the data in your reaction matrix and the data you have collected, identify your unknown as one of the five solutions. 2. Experimental Procedure, Part A.2. Describe the technique for testing the odor of a chemical. 170 ty Ken Karp A dropper pipet. 20 drops is 1 ml of solution. 3. Identify at least five observations that are indicative of a chemical reaction. Disposal: Discard the test solutions in the Waste Salts container. CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with deionized water. Discard each rinse in the Waste Salts container. The Next Step 4. Depending upon the tip of a dropper pipet, there are approximately 20 drops per milliliter of water. The Experimental Procedure, Parts A and B, indicates the addition of 5–10 drops of each solution (Figure 2.2a) to the test tubes. Calcu- late the volume range in milliliters for the solution. This experiment will enable you to better understand the importance of separation and identification,” a theme that appears throughout this manual. For example, refer to Experiments 3, 4, 37, 38, and 39. These experiments require good experimental tech- niques that support an understanding of the chemical principles involved in the separa- tion and identification of the various compounds or ions. Additionally, the amounts of a substance of interest are also determined in other experiments. Obtain a small (-50 cm) sample of soil, add water, and filter. Test the filtrate with the silver nitrate test reagent. Test a second soil sample directly with the hydrochloric acid test reagent. What are your conclusions? 62 Identification of a Compound: Chemical Properties Experiment 2 63 Experiment 2 Prelaboratory Assignment 4. Identification of unknown. Obtain an unknown for Part A from your laboratory instructor. Repeat the three tests with the reagents in Parts A.1, 2, and 3 on your unknown. On the basis of the data from the "known” solutions (collected and sum- marized in the Report Sheet matrix) and that of your unknown solution, identify the compound in your unknown solution. Identification of a Compound: Chemical Properties Disposal: Discard the test solutions in the Waste Salts container. Date Lab Sec. Name Desk No. CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with deionized water. Discard each rinse in the Waste Salts container. 1. Experimental Procedure, Part A. a. What is the criterion for clean glassware? B. Chemical Properties of Unknown Compounds b. What is the size and volume of a "small, clean test tube"? 7a1 The design of the experiment in Part B is similar to that of Part A. Therefore, 15 clean test tubes or a clean 24-well plate is necessary. 1. Preparation of solutions. On the reagent shelf are five solutions labeled 1 through 5, each containing a different compound. Use small clean test tubes or the well plate as your testing laboratory. About 1 mL of each test solution is necessary for analysis. 2. Preparation of reagents. Also on the reagent shelf are three reagents labeled A, B, and C. Use a dropper pipet (or dropper bottle) or a Beral pipet to deliver reagents A through C to the solutions. 3. Testing the solutions a. Test each of the five solutions with drops (and then excess drops) of reagent A. If, after adding several drops, you observe a chemical change, add 5-10 drops more to see if there are additional changes. Observe closely and describe any evidence of chemical change; record your observations. b. With a fresh set of solutions 1-5 in clean test tubes (or wells), test each with reagent B. Repeat with reagent C. 4. Identification of unknown. An unknown solution will be issued that is one of the five solutions from Part B.1. On the basis of the data in your reaction matrix and the data you have collected, identify your unknown as one of the five solutions. 2. Experimental Procedure, Part A.2. Describe the technique for testing the odor of a chemical. 170 ty Ken Karp A dropper pipet. 20 drops is 1 ml of solution. 3. Identify at least five observations that are indicative of a chemical reaction. Disposal: Discard the test solutions in the Waste Salts container. CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with deionized water. Discard each rinse in the Waste Salts container. The Next Step 4. Depending upon the tip of a dropper pipet, there are approximately 20 drops per milliliter of water. The Experimental Procedure, Parts A and B, indicates the addition of 5–10 drops of each solution (Figure 2.2a) to the test tubes. Calcu- late the volume range in milliliters for the solution. This experiment will enable you to better understand the importance of separation and identification,” a theme that appears throughout this manual. For example, refer to Experiments 3, 4, 37, 38, and 39. These experiments require good experimental tech- niques that support an understanding of the chemical principles involved in the separa- tion and identification of the various compounds or ions. Additionally, the amounts of a substance of interest are also determined in other experiments. Obtain a small (-50 cm) sample of soil, add water, and filter. Test the filtrate with the silver nitrate test reagent. Test a second soil sample directly with the hydrochloric acid test reagent. What are your conclusions? 62 Identification of a Compound: Chemical Properties Experiment 2 63 5. Experimental Procedure, Part A. The substances NaCl, Na2CO3, MgSO4, and NH CI, which are used for test solutions, are all soluble ionic compounds. For each substance, indicate the ions present in its respective test solution. Experiment 2 Report Sheet NaCl: Identification of a Compound: Chemical Properties Na CO2: Date Lab Sec. Name Desk No. MgSO4 A. Chemical Properties of Known Compounds Indicate your observations in the reaction matrix. Test NaCl(aq) Na2CO3(aq) NH.Cl: MgSO4(aq) NHCl(aq) H2O(1) Unknown AgNO3(aq) 2NaOH(aq) 6. Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench. Lying beside the test tubes are three labels: potassium iodide, KI; silver nitrate, AgNO3; and sodium sulfide, Na S. You are to place the labels on the test tubes using only the three solutions present. Here are your tests: • A portion of test tube 1 added to a portion of test tube 3 produces a yellow silver iodide precipitate. • A portion of test tube 1 added to a portion of test tube 2 produces a black silver sulfide precipitate. a. Your conclusions are: Test tube 1 HCl(aq) Write formulas for the precipitates that formed in Part A. (See Appendix E) Test tube 2 Part A.1 Test tube 3 Part A.2 Part A.3 b. Write the balanced equation for the formation of silver iodide, Agl, from a mix of two selected solutions provided above. Sample no. of unknown for Part A.4 Compound in unknown solution B. Chemical Properties of Unknown Compounds Indicate your observations in the reaction matrix. Sample no. of unknown for Part B.4 c. Write the balanced equation for the formation of silver sulfide, Ag S, from a mix of two selected solutions provided above. Solution No. 1 2 3 4 5 Unknown Reagent A Reagent B Reagent C Compound of unknown is the same as Solution No. 64 Identification of a Compound: Chemical Properties Experiment 2 65 Experiment 3 Water Analysis: Solids ooyoo/iStockphoto "Clear" water from streams contains small quantities of dissolved and suspended solids. • To determine the total, dissolved, and suspended solids in a water sample To determine the ions present in the solids of a water sample OBJECTIVES The following techniques are used in the Experimental Procedure: TECHNIQUES 11b 116 15b 16a 16b Laboratory Questions Circle the questions that have been assigned. 1. Identify a chemical reagent used in this experiment that can be used to distinguish solid CaCl, (soluble) from solid CaCO3 (insoluble). What is the distinguishing observation? 2. What test reagent used in this experiment will distinguish a soluble CF salt from a soluble SO - salt? What is the distinguishing observation? 3. Predict what would be observed (and why) from an aqueous mixture for each of the following (all substances are water soluble). a. potassium carbonate and hydrochloric acid b. zinc chloride and silver nitrate c. magnesium chloride and sodium hydroxide d. ammonium nitrate and sodium hydroxide 4. Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench. Lying beside the tests tubes are three labels: 0.10 M Na2CO3, 0.10 M HCl, and 0.10 M KOH. You are to place the labels on the test tubes using only the three solutions present. Here are your tests: • A few drops of the solution from test tube 1 added to a similar volume of the solution in test tube 2 produces no vis- ible reaction but the solution becomes warm. • A few drops of the solution from test tube 1 added to a similar volume of the solution in test tube 3 produces carbon dioxide gas. Identify the labels for test tubes 1, 2, and 3. 5. Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench. Lying beside the test tubes are three labels: silver nitrate, AgNO3; hydrochloric acid, HCl; and sodium carbonate, Na2CO3. You are to place the labels on the test tubes using only the three solutions present. Here is your analysis procedure: • A portion of test tube 1 added to a portion of test tube 2 produces carbon dioxide gas, CO2. • A portion of test tube 2 added a portion of test tube 3 produces a white silver carbonate precipitate. a. On the basis of your observations how would you label the three test tubes? b. What would you expect to happen if a portion of test tube 1 is added to a portion of test tube 3? 6. For individual solutions of the cations Ag+, Ba²+, Mg2+, and Cu²+, the following experimental observations were collected: NH3(aq) HCl(aq) H SO,(aq) No change White ppt No change No change No change White ppt No change No change Cu2+ Blue ppt/deep blue soln with excess No change No change *Example: When an aqueous solution of hydrochloric acid is added to a solution containing Ag", a white precipitate (ppt) forms. From these experimental observations, a. identify a reagent that distinguishes the chemical properties of Agt and Mg2+. What is the distinguishing observation? b. identify a reagent that distinguishes the chemical properties of HCl and H2SO4. What is the distinguishing observation? c. identify a reagent that distinguishes the chemical properties of Ba²+ and Cu²+. What is the distinguishing observa- tion? *d. identify a reagent that distinguishes the chemical properties of Cu2+ and Mg2+. What is the distinguishing obser- vation? INTRODUCTION Surface water is used as the primary drinking water source for many large municipali- ties. The water is piped into a water-treatment facility where impurities are removed and bacteria are killed before the water is placed into the distribution lines. The contents of the surface water must be known and predictable so that the treatment facility can properly and adequately remove these impurities. Tests are used to determine the contents of the surface water. Dissolved Solids Ag* Watershed: the land area from which the natural drainage of water occurs Ba2+ White ppt Mg2+ Water in the environment has a large number of impurities with an extensive range of concentrations. Dissolved solids are water-soluble substances, most often salts, although some dissolved solids may come from organic sources. Naturally occurring dissolved salts generally result from the movement of water over or through mineral de- posits such as limestone. These dissolved solids, characteristic of the watershed, gener- ally consist of sodium, calcium, magnesium, and potassium cations and chloride, sulfate, bicarbonate, carbonate, bromide, and fluoride anions. Anthropogenic (human- related) dissolved solids include nitrates from fertilizer runoff and human wastes, phos- phates from detergents and fertilizers, and organic compounds from pesticides, sewage runoff, and industrial wastes. Dissolved salts can be problematic in potable water. Typical dissolved salt concentra- tions range from 20 to 1,000 mg/L, although most waters are less than 500 mg/L. High concentrations also indicate “hard” water (Experiment 21), which can clog pipes and industrial cooling systems. Also, high concentrations of dissolved salts can cause diarrhea or constipation for some people. Salinity, a measure of the total salt content in a water sample, is expressed as the grams of dissolved salts per kilogram of water or as parts per thousand (ppt). The average ocean salinity is 35 ppt, whereas freshwater salinity is usually less than 0.5 ppt. Brackish water, where fresh river water meets salty ocean water, varies from 0.5 ppt to 17 ppt. For water samples with low organic levels, the salinity of a water sample approximates that of total dissolved solids (TDS) content. Parts per thousand (ppt): 1g of substance per 1,000g (1 kg) of sample 66 Identification of a Compound: Chemical Properties Experiment 3 67