Quiz: le Châtelier – Concentration

Consider the following equation (in solution CoCl42- is blue, and Co2+ is pink):

CoCl42- (aq)   Co2+ + 4Cl- (aq)

1.Which of the following solid substances would NOT demonstrate the common ion effect if it was added to the above solution?
  NaCl (s)           K2SO4          CaCl2          CoSO4

2. If you had a method of adding more Cl- (aq) to the reaction, then you would expect to find the solution responding, as:

Applied Stress Le Châtelier's Principle Prediction of Response to Stress
CoCl42- Co2+ + 4Cl-
Increase [Cl- (aq)] Increase Increase Decrease
Increase [Cl- (aq)] Decrease Increase Increase
Increase [Cl- (aq)] Decrease Decrease Increase
Increase [Cl- (aq)] Increase Decrease Decrease

3.  Which of these would you expect to happen if you added some solid NaCl to the solution?
Nothing.   There is no NaCl in this reaction
It would become more pink
It would become more blue
It would become more clear

Consider the following solubility equation:

Ca(OH)2(s) Ca2+(aq) + 2OH-(aq)

4. What would be the effect on the reaction of adding more OH- (aq) ions?
a) the [OH-] will decrease below its original amount
b) the [Ca(OH)2 (s)] will increase
c) there will be a decrease in [Ca2+(aq)]
d) there will be no effect

5. What would be the effect on the reaction of adding more solid Ca(OH)2?
a)  the [OH-] will increase above its original amount
b) the [Ca(OH)2 (s)] will increase
c) there will be an increase in [Ca2+(aq)]
d) all of the above are true
e) there will be no effect

Consider the reaction between hydrogen and chlorine gases

H2 (g) + Cl2 (g) 2HCl (g)

6. According to le Châtelier's principle, adding some more Cl2 (g) to the reaction container should:

  a) cause the reaction to shift to the left
  b) cause the reaction to shift to the right
  c) cause no change in the reaction