15 extra multiple-choice questions for Ionic Equilibrium (12th Standard Chemistry, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
According to the Arrhenius theory, which of the following best describes a base?
- A. A substance that donates a proton to another substance
- B. A species that accepts an electron pair
- C. A substance that dissociates to give hydroxyl ions in waterCorrect
- D. A species that donates a proton to water
Explanation. Arrhenius defined bases as substances that increase the concentration of hydroxyl ions (\(OH^-\)) when dissolved in aqueous solutions through dissociation.
Q2
In the Lowry-Bronsted concept, what is the conjugate acid formed when \(H_2O\) acts as a base and accepts a proton?
- A. \(OH^-\)
- B. \(H_3O^+\)Correct
- C. \(H_2O_2\)
- D. \(H_2\)
Explanation. A conjugate acid is produced when a base accepts a proton. When a water molecule gains a proton, it becomes the hydronium ion.
Q3
Which of the following is classified as a Lewis acid due to being an electron-deficient molecule?
- A. \(NH_3\)
- B. \(H_2O\)
- C. \(BF_3\)Correct
- D. \(F^-\)
Explanation. Boron trifluoride is an electron-deficient molecule that can accept an electron pair from a donor, which defines it as a Lewis acid.
Q4
If an aqueous solution has a hydronium ion concentration \([H_3O^+]\) of \(1 \times 10^{-4}\) M, what is its pH?
- A. 4Correct
- B. 10
- C. 7
- D. 14
Explanation. pH is the negative base-10 logarithm of the hydronium ion concentration. For a value of \(10^{-4}\) M, the negative log is 4.
Q5
The ionic product of water (\(K_w\)) is known to increase when which of the following occurs?
- A. Pressure is decreased
- B. Temperature is increasedCorrect
- C. A strong acid is added
- D. A strong base is added
Explanation. The auto-ionisation of water is an endothermic process. Increasing temperature shifts the equilibrium toward ion formation, which increases the value of the constant \(K_w\).
Q6
According to Ostwald's dilution law, the degree of dissociation (\(\alpha\)) of a weak electrolyte is:
- A. Directly proportional to the molar concentration
- B. Inversely proportional to the square root of concentrationCorrect
- C. Independent of the volume of the solution
- D. Equal to the square of the dissociation constant
Explanation. Ostwald's dilution law states that for weak electrolytes, the degree of dissociation is inversely proportional to the square root of the concentration.
Q7
What is the term for the suppression of a weak acid's dissociation by adding a salt that contains a shared ion?
- A. Buffer action
- B. Salt hydrolysis
- C. Common ion effectCorrect
- D. Electrolysis
Explanation. The common ion effect describes the reduction in dissociation of a weak electrolyte when a strong electrolyte with a common ion is added.
Q8
Which of the following combinations would produce an acidic buffer solution?
- A. \(NH_4OH\) and \(NH_4Cl\)
- B. \(CH_3COOH\) and \(CH_3COONa\)Correct
- C. \(HCl\) and \(NaCl\)
- D. \(NaOH\) and \(NaCl\)
Explanation. An acidic buffer consists of a mixture of a weak acid and its conjugate base, such as acetic acid and sodium acetate.
Q9
Identify the Henderson-Hasselbalch equation used specifically to calculate the pOH of a basic buffer.
- A. \(pH = pK_a + \log \frac{[salt]}{[acid]}\)
- B. \(pOH = pK_b + \log \frac{[salt]}{[base]}\)Correct
- C. \(pH = pK_w - pOH\)
- D. \(K_h = \frac{K_w}{K_a}\)
Explanation. The equation for a basic buffer relates pOH to the \(pK_b\) of the weak base and the logarithm of the salt-to-base concentration ratio.
Q10
An aqueous solution of ammonium chloride (\(NH_4Cl\)) is acidic because of the hydrolysis of which species?
- A. The \(Cl^-\) ion
- B. The \(NH_4^+\) ionCorrect
- C. The entire \(NH_4Cl\) molecule
- D. Water molecules only
Explanation. Ammonium chloride is a salt of a weak base and strong acid. The ammonium cation reacts with water, increasing the hydronium ion concentration.
Q11
Which of the following salts will form a neutral aqueous solution with a pH of 7 at 298K?
- A. \(CH_3COONa\)
- B. \(NH_4Cl\)
- C. \(NaCl\)Correct
- D. \(Na_2CO_3\)
Explanation. Sodium chloride is a salt of a strong acid and a strong base. Neither ion undergoes hydrolysis, so the resulting solution remains neutral.
Q12
For the sparingly soluble salt silver chromate (\(Ag_2CrO_4\)), the solubility product (\(K_{sp}\)) expression is:
- A. \([Ag^+][CrO_4^{2-}]\)
- B. \([Ag^+][CrO_4^{2-}]^2\)
- C. \([Ag^+]^2[CrO_4^{2-}]\)Correct
- D. \([Ag^+] + [CrO_4^{2-}]\)
Explanation. The \(K_{sp}\) is the product of ion concentrations, with the silver ion concentration squared because its stoichiometric coefficient in the dissociation equation is 2.
Q13
If 's' represents the molar solubility of \(Ag_2CrO_4\) in water, how is \(K_{sp}\) related to 's'?
- A. \(K_{sp} = s^2\)
- B. \(K_{sp} = 4s^2\)
- C. \(K_{sp} = 4s^3\)Correct
- D. \(K_{sp} = 27s^4\)
Explanation. Since the salt dissociates into \(2Ag^+\) and \(1CrO_4^{2-}\), the expression is \((2s)^2 \times (s) = 4s^3\).
Q14
In which condition will a precipitate definitely form when two solutions are mixed?
- A. Ionic Product is equal to \(K_{sp}\)
- B. Ionic Product is less than \(K_{sp}\)
- C. Ionic Product is greater than \(K_{sp}\)Correct
- D. Ionic Product is zero
Explanation. Precipitation occurs when the solution becomes supersaturated, meaning the product of the existing ion concentrations exceeds the solubility product constant.
Q15
Which of the following species acts as a Lewis base by donating an electron pair to form a coordinate bond?
- A. \(Fe^{3+}\)
- B. \(BF_3\)
- C. \(NH_3\)Correct
- D. \(AlCl_3\)
Explanation. Ammonia (\(NH_3\)) has a lone pair of electrons on the nitrogen atom that it can donate to an electron acceptor, making it a Lewis base.
About these Ionic Equilibrium questions
These are the Additional multiple-choice questions for Ionic Equilibrium from the Tamil Nadu State Board (Samacheer Kalvi) 12th Standard Chemistry syllabus. Each question shows the correct option and an original, step-by-step explanation so you understand the method, not just the answer. Use the answer key above to jump to any question, then take the practice test to check yourself under exam-like conditions.
Frequently asked questions
How many MCQs are there in Ionic Equilibrium?
This chapter has 15 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Chemistry MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Ionic Equilibrium book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
