4C: EFFECT OF TEMPERATURE NOTE You must wear disposable gloves for this test 1.

Question

4C: EFFECT OF TEMPERATURE NOTE You must wear disposable gloves for this test 1. Prepare a solution containing equal amounts of the pink Co(H,0)." ion and the blue CoCla ion by placing 10 ml of 0.4 M Co(NO,)2 solution in a large test tube and adding 6 ml of 12 M HCI. CAUTION: 12 M HCI is highly corrosive! It must only be used in the fume hood 2. Divide this solution about equally into three test tubes. 3. Place one test tube on ice and another in hot water. The third test tube is kept at room temperature to serve as a reference color. Incubate 5-10 minutes. 4. Record your observations on the report form

Explanation / Answer

For the system the color change would show,

system                   Color                   Predominant complex

Ice bath             dark pink                            [Co(H2O)6]^2+

hot water         dark purple/blue                      CoCl4^2-

The reaction for the formation of CoCl4^2- from [Co(H2O)6]^2+ is exothermic in nature. The transformation occurs in hot water (heat supplied) whereas in cold water no such reaction occurs and we have predominantly [Co(H2O)6]^2+ as the species present in solution.

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