Experiment 1 Analysis of Some Common Anions IUG, 2019

OBJECTIVE To study the reactions of five common anions, 𝑃𝑂4 3– , SO4 2– , 𝐶𝑙 – , 𝐼 – and 𝐶𝑂3 2– .

quantitative analysis Types of Analysis qualitative analysis which is the determination of the types of the species present in a sample. quantitative analysis which is the determination of how much of a species is present in a sample.

Types of reactions encountered in qualitative analysis 1-Precipitation reactions 2-Complex ion formation reactions 3-Redox reactions 4-Acid-base reactions Some means of identifying ions by qualitative analysis 1-Colour changes 2-Evolution of gas 3-Change in pH (acidity or basicity) 4-Precipitate

A salt consists of a cation (positive ion) and an anion (negative ion). Because anion analysis is somewhat simpler than cation analysis, we shall begin our work in qualitative analysis with methods of identifying five common anions in solution. phosphate, 𝑃𝑂4 3– chloride, 𝐶𝑙 – carbonate, 𝐶𝑂3 2– sulfate, SO4 2– iodide, 𝐼 –

𝐵𝑎 2+ (aq) + 𝐴 𝑛− (aq) 𝐵𝑎 𝑛 𝐴 2 (𝑆) PROCEDURE A. CHEMICAL REACTIONS OF INDIVIDUAL ANIONS 1. The Ba(NO3)2 Test 1. Take a set of five small test tubes. After cleaning them, label them 1 through 5, and place 4-5 drops of one of the known solutions in each tube. 2. Make each solution slightly basic by adding 1 drop of 6 M ammonia (NH3). Making sure the solution is thoroughly mixed, test the basicity of the solution with litmus paper as demonstrated by your instructor. 3. When the solutions are basic, note any changes that have occurred, and enter your observations in your lab book. 4. Add 2-3 drops of 0.2 M Ba(NO3)2 to form precipitates between Ba2+ and some of the anions. 𝐵𝑎 2+ (aq) + 𝐴 𝑛− (aq) 𝐵𝑎 𝑛 𝐴 2 (𝑆) Record observations on the color and texture or appearance of the precipitates in your report form.

5. Some of the precipitates you have formed will dissolve in acid 5.Some of the precipitates you have formed will dissolve in acid. In each case where a precipitate has formed with Ba(NO3)2, make the solution acidic with 6 M HCl (blue litmus paper should turn red in acid). Be sure to mix the solution well after adding acid! (The most common error made in qualitative analysis laboratory is to fail to mix solutions completely!) Record your observations. 6.Discard the solutions from the tests above and clean the test tubes thoroughly.

Ag+(aq) + anion(aq) [Ag(anion)](s) 2. The AgNO3 Test 1. Once again prepare five test tubes, each containing 4-5 drops of one of the known solutions. 2. Dilute each solution with about 1 mL of distilled water and then add 2 drops of silver nitrate, AgNO3, solution. Now you should see some of the anions combine with silver ion to again produce insoluble precipitates. Ag+(aq) + anion(aq) [Ag(anion)](s) Once again record your observations in your report form. Divide the precipitate that may form into two parts in two separates test tubes. 3. After observing the precipitates that may form with some anions, attempt to dissolve these precipitates in acid. This time, however, you must use nitric acid, HNO3. Add 4 drops of 3 M HNO3 to each precipitate with silver ion, mix well, and note the results. 4. Test the solubility of each precipitate also with ammonia. Add 2-4 drops of 6 M NH3 to each precipitate with silver ion, mix well, and note the results. Again record your observations

B. Qualitative Analysis of An Unknown Salt The unknown sample is pure sample. Sample A contains one salt, a salt that has only one of the five anions. 1. Transfer a small amount (20-40 crystals) of the unknown salt into a clean test tube. 2. Half-fill the test tube with distilled water and shake for about 30 s. 3. Use this solution to perform the previous tests as described in parts A. 1 and A. 2, compare your observations to decide which anion present in your unknown.