Qualitative Analysis: Solubility Data Table

Qualitative Analysis Lab
Solubility Data Table Cations | Ag+ | Pb2+ | Cu2+ | Ni2+ | Ba2+ | NaCl | White ppt, AgCl(soluble in 12M HCl, soluble in sln of good complexing agent, 6M NH3) | White ppt, PbCl2(soluble in hot water, soluble in 12M HCl, soluble in sln of xs NaOH) | Soluble – no ppt | Soluble – no ppt | Soluble – no ppt | Na2CO3 | White ppt, Ag2CO3(soluble in 6M HCl, soluble in sln of good complexing agent) | White ppt, PbCO3(soluble in 6M HCl, soluble in sln of good complexing agent) | Blue ppt, CuCO3(soluble in 6M HCl, soluble in sln of good complexing agent) | Green ppt, NiCO3(soluble in 6M HCl, soluble in sln of good complexing agent) | White ppt, BaCO3(soluble in 6M acetic acid, soluble in 12M HCl) | NH3 | Brown ppt, Ag2O(soluble
in xs NH3 as Ag(NH3)2+) | White ppt, Pb(OH)2(soluble in 6M HCl, soluble in sln of good complexing agent) | Pale Blue ppt, Cu(OH)2(soluble in xs NH3 as Cu(NH3)42+, deep blue complex | Blue-purple color of Ni(NH3)62+ complex | ? | NaOH | Brown ppt, Ag2O(soluble in 6M HCl, soluble in sln of good complexing agent) | White ppt, Pb(OH)2(soluble in 6M HCl, soluble in sln of good complexing agent,sol.
in xs NaOH) | Pale Blue ppt, Cu(OH)2(soluble in 6M HCl, soluble in sln of good complexing agent) | Green Gel becomes crystalline upon standing, Ni(OH)2 | ? | S2- (acidic pH = 0) | Black ppt, Ag2S(soluble in hot 6M HNO3) | Black ppt, PbS(soluble in hot 6M HNO3) | Black ppt, CuS(soluble in hot 6M HNO3) | No ppt | | S2- (basic pH = 9) | Black ppt, Ag2S(soluble in hot 6M HNO3) | Black ppt, PbS(soluble in hot 6M HNO3) | Black ppt, CuS(soluble in hot 6M HNO3) | Black ppt, NiS(soluble in hot 12M HCl) | |
Perform the Separation/Identification Experiment as follows;
• Read through the Discussion and Cations sections on pages 450 to 452, skipping the last paragraph on page 452. This is where you will get your Purpose Statement and Background information for your Prelab. Do the Prelab questions 1, 2, 3, 4 on pages 435 and 436. Also do the Prelab questions 1, 2, 3, 6, 7 on pages 455 and 456.
• Mix a Known from 1 mL each of the standard solutions of all 5 cations. You will run the separation/analysis of your Unknown and Known side by side. Record all observations for both after each
step.
• Your Known will contain all of the following cations:
NH4+, Ag+, Cu2+, Ni2+ and Ca2+
Your Unknown will contain any 2 of those cations.
• Get an unknown from your TA and record the # of your Unknown _____.

• You need to fill in the Flowchart provided using only the above cations and their reactions/solubilities for separation and identification.
Refer to the Cation flow chart on page 426 as well as the one on page 451 when doing this.

• PROCEDURE

Preliminary Test for NH4+
In a separate clean evaporating dish, place 10 drops of your Unknown. (also do this test on your Known as a comparison) Moisten a strip of red litmus paper and smooth it onto the bottom of a watch glass. Add 10 drops of 3M NaOH to the evaporating dish, swirl it to mix the solutions and place the watch glass, litmus paper side down, over the dish. After a few minutes, the presence of NH4+ is confirmed when the litmus paper turns blue.

Separation and Analysis of Group I – Ag+
Follow the steps in G1-1 on page 453. Be very careful to ensure ALL of the Ag+ precipitates or it can be carried over and form a precipitate later, obscuring the presence/absence of other cations.
The formation of a white precipitate confirms the presence of Ag+. The supernatant liquid (supernatant I) is saved in a fresh test tube for analysis to establish the presence/absence of Group II, III and IV cations.

Analysis of Group II – Cu2+
To the supernatant I add 10 drops of 1M thioacetamide solution and let the test tube sit in a boiling water bath for 10 minutes IN A HOOD. The S2- ions evolved in solution cause the Cu2+ ions to precipitate from the acidic solutions as CuS. Formation of the black CuS precipitate confirms the presence of Cu2+. Centrifuge the tube and save the supernatant liquid (supernatant II) in a fresh test tube for analysis to establish the presence/absence of Group III and IV cations.

Analysis of Group III – Ni2+
Add 15M NH3 solution dropwise to the supernatant II solution until basic (test with red litmus paper).
The NiS should become insoluble and the formation of this black precipitate confirms the presence of Ni2+. Ca2+ will remain in solution. Centrifuge the test tube and decant the supernatant liquid (supernatant III) into a clean test tube for further analysis of Ca2+ (Group IV). Wash the precipitate with 1 mL of distilled water, centrifuge and discard the wash solution. Carefully add 20 drops of 12M HCl and heat the test tube in a hot water bath in the hood. If precipitate is still present, add 3 more drops of 12M HCl and continue heating. Remove the test tube from the heat and CAREFULLY add 6M NH3 solution until neutral. Add 3 drops of dimethylglyoxime solution and watch for the formation of a cherry red precipitate – this confirms the presence of Ni2+.

Analysis of Group IV – Ca2+ Take the supernatant III and pour half of the solution into a second clean test tube. To one test tube add drops of 1M Na2CO3 solution and watch for formation of a white CaCO3 precipitate. (Ca2+ would also be confirmed by; to the second test tube add drops of 1M K2CrO4 solution and watch for formation of a canary yellow CaCrO4 precipitate.) The other test tube of solution can be used for a flame test – reddish flash confirms Ca2+.

Use the Outline below when collecting your data and writing your lab
report.
Separation Flow Chart for Ag+, Cu2+, Pb2+, Ni2+, Ca2+
[You need to draw a flow chart like the one on page 361 of your book, including the cations of interest and the reagents necessary.]

Table of Data
Make a table to enter data/observations for both the Known and Unknown.
You need enough space in the table to include things like the following; 1. No observable change.( N.R. for no reaction.) 2. A precipitate forms – e.g. powdery green ppt forms 3. The solution changes color; e.g. green sln blue purple sln 4. Gas bubbles evolve. Reagent added | Observations for Known | Observations for Unknown | Without addition | (record color) | (record color) | 6M HCl | White ppt, clear green/ blue solution | | Hot water | ppt from above dissolvedetc | |

In your lab report, since you will have identified your cations, you need to write the identity of precipitates formed in both the Known and the Unknown.

Cations present: ____________________

Basis for this conclusion:

Postlab Question.
You are given an unknown solution that may contain Ag+ or Ba2+ or both. Outline an efficient separation procedure with no unnecessary steps to separate and confirm the presence/absence of these ions.
Also do Postlab question 1 on page 506.