Question

For the reaction: mg(oh)₂ (s) ⇌ mg²⁺ (aq) + 2 oh⁻ (aq), what will happen when mg(oh)₂ is added?

1) The reaction will shift to the left
2) The reaction will shift to the right
3) The reaction will remain at equilibrium
4) The reaction will stop

Answer 1

Adding more Mg(OH)2 to its dissociation equilibrium causes the reaction to shift to the right, increasing the concentration of Mg²⁺ and OH⁻ ions in solution.

Step-by-step explanation:

When Mg(OH)2 is added to the equilibrium system Mg(OH)2 (s) ⇌ Mg²⁺ (aq) + 2 OH⁻ (aq), Le Chatelier's Principle indicates that the system will respond to oppose the change. In this case, adding more magnesium hydroxide, which is a solid, will shift the equilibrium to the right. This occurs to reduce the concentration of the added compound by dissolving more of it, increasing the concentration of Mg²⁺ and OH⁻ ions in solution.

If a common ion such as Mg²⁺ were added instead of Mg(OH)2, the reaction would shift to the left, leading to a decrease in the concentration of hydroxide ions and an increase in the amount of undissolved magnesium hydroxide. Similarly, an addition of OH⁻ ions would have the same leftward shift effect due to the common ion effect.