Question

Use the equation of sodium chloride dissolving in water to complete the activity.

NaCl(s)⇌Na+(aq)+Cl−(aq)

A student prepares a saturated sodium chloride solution. The student adds concentrated sodium hydroxide (NaOH
) to the solution until a precipitate forms. What is happening with the equilibrium? In three to five sentences, explain your answer.

(4 points)

Short Answer Rubric (4 points)
Points Awarded Criteria
4
The answer is very clear.

The answer is fully supported by details.

There may be a few errors in grammar, usage, or mechanics. Errors do not interfere with meaning.

3
The answer is mostly clear.

The answer is supported by mostly relevant details.

There are a few errors in grammar, usage, or mechanics. Errors do not interfere with meaning.

2
The answer is somewhat clear.

Details are weak or not related.

There are some errors in grammar, usage, and mechanics. Errors interfere with meaning.

1
The answer is not clear.

There are few or no supporting details.

There are many errors in grammar, usage, and mechanics. Errors interfere with meaning.

0 The question is not answered.
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Answer 1

Adding concentrated NaOH to the saturated NaCl solution increases the concentration of the common ion Na+. By Le Chatelier’s principle the equilibrium NaCl(s) ⇌ Na+(aq) + Cl−(aq) shifts to the left, so Na+ and Cl− recombine and solid NaCl precipitates. The OH− does not remove Cl− (no weak-acid/base reaction here), so the precipitation is due to the common-ion effect reducing NaCl solubility.