Question

consider the following system at equilibrium. caco₃(s) ⇌ ca²⁺(aq) + co₃²⁻(aq) the addition of which compound will cause a shift in equilibrium because of a common - ion effect? ccl₄ co₂ cuso₄ na₂co₃

Explanation:

Step1: Understand common - ion effect

The common - ion effect occurs when an ion is added to a solution that already contains that ion, causing a shift in equilibrium according to Le - Chatelier's principle. In the given equilibrium $CaCO_3(s)
ightleftharpoons Ca^{2 + }(aq)+CO_3^{2 - }(aq)$, we are looking for a compound that will add either $Ca^{2+}$ or $CO_3^{2 - }$ ions.

Step2: Analyze each option

• $CCl_4$: Does not dissociate into $Ca^{2+}$ or $CO_3^{2 - }$ ions in water as it is a covalent compound.
• $CO_2$: Does not dissociate into $Ca^{2+}$ or $CO_3^{2 - }$ ions in water to cause a common - ion effect in this system.
• $CuSO_4$: Dissociates into $Cu^{2+}$ and $SO_4^{2 - }$ ions, not $Ca^{2+}$ or $CO_3^{2 - }$ ions.
• $Na_2CO_3$: Dissociates in water as $Na_2CO_3(s)

ightarrow 2Na^{+}(aq)+CO_3^{2 - }(aq)$. It adds $CO_3^{2 - }$ ions which is a common ion in the given $CaCO_3$ equilibrium system.

Answer:

D. $Na_2CO_3$