Explain your observations in Step 1. Step 2a Step 2b Step 2c Step 3 a and b Expe

Question

Explain your observations in Step 1.
Step 2a
Step 2b
Step 2c
Step 3 a and b
Experiment 22 Properties of Systems in Chemical Equilibrium-Le Chitelier's Principle177 D. Dissolving Insoluble Solids 1. Observations on addition of a drop of 6 M NaOH to Zn(NO), solution: 2. Effect on solubility of Zn(OH) a. of added HCl solution b. of added NaOH solut c. of added NH, solution Observations on addition of one drop of 6 M NaOH to Mg(NO), solution: Effect on solubility of Mg(OH), a of added HCl solution b. of added NaOH 3. c. of added NH, solution Explain your observations in Step 1.(Consider Reaction 8: how is it affected by addition of OH ion?) In Step 2(a), how does an increase in [H] affect Reaction 3? (What does that do to Reaction 8?) Explain your observations in Step 2(a). In Step 20b), how does an increase in (OH ] affect Reaction 97 What does that do to Reaction 8? Explain your observations in Step 2(b). In Step 2(c), how does an increase in [NH,J affect Reaction 10? What does that do to Reaction 8? Explain your observations in Step 2(c). In Step 3, you probably found that Mg(OH), was similar in some ways in its behavior to that of Zn(OH), but different in others. How was it similar? Explain that similarity. (In particular, why would any insoluble hydroxide tend to dissolve in acidic solution?) a. b. How was it different? Explain that difference. (In particular, does Mg appear to form complex ions with OH and NH,? What would we observe if it did? If it did not?)

Explanation / Answer

Step 1

You added NaOH to a solution containing Zn(NO3), the reaction is as follows

2 NaOH + Zn(NO3) ==== Zn(OH)2 (s)+ 2 NaNO3

Zn(OH)2 is a precipitate that is why you see it cloudy

Step 2a

The Zn(OH)2 dissociates like Zn + 2 OH, if you add H+ then you will neutralize the OH- ions and the equilibrium will shift to the right in order to form Zn+2

Step 2 b

If you add OH- ions then you will shift the equilibrium to the left

Zn(OH)2 === Zn + 2 OH, so you will produce more Zn(OH)2

that is why you see more precipitate

Step 2c

When you add NH3 the reaction is

Zn(OH)2 + 4NH3 ==== [Zn(NH3)4]+2 (aq)

This compound will redissolve to form a complex, you should not be able to see a ppt

step 3 a and 3b are the same as step 2 a and 2 b

Mg(NO3)2 + 2NaOH ==== Mg(OH)2 + 2NaNO3

Mg(OH)2 is a ppt

it dissociates like

Mg(OH)2 ==== Mg+2 + 2 OH

if you add OH the equilibrium will shift to the left and you will produce more ppt

IF you add H+ then the OH will be neutralized and the equilibrium will shift to the right until no more ppt is present.

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