7 past paper MCQs on Common Ion Effect, from the Chemical Equilibrium unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.The decrease in solubility of a salt in a solution that already contains an ion common to that salt is known as: (MDCAT 2022)
Correct answer: (c) common ion effect
The added common ion shifts the dissolution equilibrium back towards the solid.
2.Q.83 The decrease in solubility of the salt in a solution that already contains an ion common to that salt is known as: (UHS MDCAT 2023)
Correct answer: (c) Common ion effect
Adding a common ion drives the dissolution equilibrium back, which is the common ion effect.
3.When Hydrogen Chloride gas passes through saturated brine, it increases the concentration of: (PMC MDCAT 2022)
Correct answer: (d) Chloride ion
The added chloride is the ion common to the salt, so it drives the sodium chloride out of solution.
4.Common Ion Effect finds its extensive application in: (PMC MDCAT 2022)
Correct answer: (d) Salt analysis
The salts of a group are precipitated by adding a common ion, which is how they are separated.
5.What will happen to the KClO3 when KCl is added to its solution in water? (PMC MDCAT 2022)
Correct answer: (b) Its solubility decreases
The potassium ion is common to both salts, so it drives the chlorate out of solution.
6.Suppression of ionization means: (PMC Practice 2021)
Correct answer: (a) Decreasing ionization
Adding a common ion pushes the ionization equilibrium back, which suppresses it.
7.Purification of table salt (NaCl) by passing HCl gas through its saturated aqueous solution is an example of: (PMC MDCAT 2020)
Correct answer: (c) Common ion effect
The added chloride is the ion common to the salt, so the sodium chloride is driven out of solution.