Using your predictions in the prelab question 4 and your observations for part C

Question

Using your predictions in the prelab question 4 and your observations for part C, explain what was occurring in each test tube.

Add 2 mL of 0.1 M Zn(NO3)2 to three different test tubes.

Add 1 drop of 6 M NaOH to each tube and record observations.

To the first test tube, add 6 M NaOH drop by drop and record your observations.

To the second tube, add 6 M HCl drop by drop and record your observations.

To the third tube, add 6 M NH3 drop by drop and record your observations.

What was occuring in each test tube?

Explanation / Answer

1. When 1 drop of 6M NaOH solution added to each test tube of Zinc nitrate solution Zn wiill precipitate ( white )as Zinc hydroxide

Zn^2+ + 2OH^- -----------> Zn(OH)2

2.When 6M NaOH is added drop by drop to the first test tube , the precipitated Zinc hydroxide will dissolve by the formation of Zincate ion ( the soln is colorless)

Zn(OH)2 + 2OH^-2 ----------> [Zn(OH)4]^2-

3.When 6M HCl added drop by drop to the second test tube , the precipitated Zinc hydroxide will dissolve to form colorless Zinc chloride solution

Zn(OH)2 + 2HCl ---------- > Zn(Cl)2 + H2O

4. When ammonia is added drop by drop to the third test tube Zinc hydroxide will dissolve by the formstion of ammine complex( the solution is colorless )

Zn(OH)2 + 4NH3 ---------- >[ Zn(NH3)4]^2+ + 2OH^-

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