Rewrite the section of lab 120 assigned to you (see below) so that it is clear to you and you could perform the experiment in lab. To save some typing time, at the end of this page to procedure as printed is given. Cut and paste your section into a Word document and revise as you feel appropriate. The assignment are as follows: If your last name begins with letters
A-E, rewrite the chloride test procedure
F-L, rewrite the sulfate test procedure
M-Q, rewrite the carbonate test procedure
R-Z, rewrite the nitrate test procedure
Due Tuesday October 6, 2009
1. Test for Chloride Ions
To 10 drops of the solution to be tested (either known or unknown) add a few drops of 6 M HNO3. Test with litmus paper to make sure the solution is slightly acidic. Add 5 drops of 0.1 M AgNO3 and stir well. Centrifuge to pack any precipitate that forms. Add an additional drop or two of 0.1 M AgNO3 to test for complete precipitation. If necessary centrifuge again. Discard the supernatant liquid. Wash the precipitate with deionized water to remove excess acid and silver ions. To the precipitate add 10 drops of H2O and 4 drops of 6 M NH4OH, stir well. If a precipitate remains, centrifuge and pour the clear supernatant into a clean test tube. Acidify the supernatant with 6 M HNO3. A white precipitate of AgCl confirms the presence of chloride.
2. Test for Sulfate Ions
To 10 drops of the solution add 6 M HNO3 dropwise until the solution is slightly acidic. Add 5 drops of 0.1 M BaCl2 solution. A white precipitate of BaSO4 indicates the presence of SO42-.
3. Test for Carbonate Ions
Fit a test tube with a stopper and bent delivery tube. Place 3 mL of the test solution in this tube. Insert the delivery tube into a test tube containing limewater, Ca(OH)2. When ready remove the stopper enough to add a small amount of concentrated HCI. Replace the stopper quickly and gently boil the acidic solution to drive any CO2 into the limewater. A white precipitate in the limewater indicates CO32- in the test solution.
4. Test for Nitrate Ion
Acidify 1 mL of the test solution with 3 M H2SO4 and add 10 drops of saturated FeSO4. Tilt the test tube at about a 45 angle and pour about 1 mL of concentrated H2SO4 slowly down the side of the test tube. (Caution: Concentrated (18 M) H2SO4 is very corrosive and can cause severe burns to the skin. If any touches your skin, wash immediately and thoroughly with water.) Be careful not to mix the two liquids. A brown ring at the interface between the two liquids indicates the presence of nitrate ions.