JEE Chemistry Ionic Equilibrium MCQs Set 30

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Access targeted multiple-choice questions for Ionic Equilibrium designed to align with the latest JEE academic syllabus for JEE Chemistry. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Chapter-wise Objective Questions: Ionic Equilibrium

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Multiple Choice Questions

Question 1: The pH of a 0.05 M \( \ce{Ba(OH)2} \) solution (assume complete dissociation) is
(a) 12
(b) 13
(c) 1
(d) 12.96
Show Answer & Explanation

Answer: (b) 13

Explanation:
1. \( \ce{Ba(OH)2} \) gives two \( \ce{OH-} \) per formula unit: \( [OH^-]=0.1 \) M.
2. pOH = 1, so pH = 13.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 2: In mixing acetic acid and sodium acetate, the ratio of the salt to the acid is increased ten times. Then the pH of the solution
(a) increases by one
(b) decreases by one
(c) decreases ten-fold
(d) increases ten-fold
Show Answer & Explanation

Answer: (a) increases by one

Explanation:
1. \( pH=pK_a+\log([salt]/[acid]) \).
2. A ten times larger ratio adds \( \log10=1 \) to the pH.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 3: If the pH of a solution of an alkali metal hydroxide is 13.6, the concentration of hydroxide is
(a) between 0.1 M and 1 M
(b) more than 1 M
(c) less than 0.001 M
(d) between 0.01 M and 0.1 M
Show Answer & Explanation

Answer: (a) between 0.1 M and 1 M

Explanation:
1. pOH = 0.4, so \( [OH^-]=10^{-0.4}=0.40 \) M.
2. This lies between 0.1 M and 1 M.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 4: The \( pK_a \) of acetylsalicylic acid (aspirin) is 3.5. The pH of gastric juice in the human stomach is about 2-3 and the pH in the small intestine is about 8. Aspirin will be
(a) unionized in the small intestine and in the stomach
(b) completely ionized in the small intestine and in the stomach
(c) ionized in the stomach and almost unionized in the small intestine
(d) ionized in the small intestine and almost unionized in the stomach
Show Answer & Explanation

Answer: (d) ionized in the small intestine and almost unionized in the stomach

Explanation:
1. In the stomach pH < \( pK_a \), so the acid stays mostly unionized.
2. In the intestine pH is far above \( pK_a \), so it is mostly ionized.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 5: If the \( [H^+] \) of a solution is increased 10 times, its pH will
(a) increase by one
(b) remain unchanged
(c) decrease by one
(d) increase by 10
Show Answer & Explanation

Answer: (c) decrease by one

Explanation:
1. \( pH=-\log[H^+] \): a ten-fold rise in \( [H^+] \) lowers pH by 1.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 6: A weak acid solution is diluted by adding an equal volume of water. Which of the following will not change?
(a) strength of the acid
(b) the value of \( [H_3O^+] \)
(c) pH of the solution
(d) the degree of dissociation of the acid
Show Answer & Explanation

Answer: (a) strength of the acid

Explanation:
1. Acid strength (\( K_a \)) depends only on temperature.
2. \( [H_3O^+] \), pH and the degree of dissociation all change on dilution.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 7: Assuming complete dissociation, which of the following aqueous solutions have the same pH? (i) 100 mL of 0.01 M HCl, (ii) 100 mL of 0.01 M \( \ce{H2SO4} \), (iii) 50 mL of 0.01 M HCl, (iv) a mixture of 50 mL of 0.02 M \( \ce{H2SO4} \) and 50 mL of 0.02 M NaOH
(a) (i), (iii) and (iv)
(b) (i) and (ii) only
(c) (ii), (iii) and (iv)
(d) (i) and (iii) only
Show Answer & Explanation

Answer: (a) (i), (iii) and (iv)

Explanation:
1. (i) and (iii): \( [H^+]=0.01 \) M, pH = 2.
2. (ii): \( [H^+]=0.02 \) M, pH = 1.7.
3. (iv): 2 meq of \( \ce{H+} \) - 1 meq of \( \ce{OH-} \) = 1 meq in 100 mL gives 0.01 M, pH = 2.
4. So (i), (iii) and (iv) match.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 8: The hydrogen ion concentration of 0.006 M benzoic acid solution is approximately (\( K_a=6\times10^{-5} \))
(a) \( 0.6\times10^{-4} \)
(b) \( 6\times10^{-4} \)
(c) \( 6\times10^{-5} \)
(d) \( 3.6\times10^{-4} \)
Show Answer & Explanation

Answer: (b) \( 6\times10^{-4} \)

Explanation:
1. \( [H^+]=\sqrt{K_aC}=\sqrt{6\times10^{-5}\times6\times10^{-3}}=\sqrt{3.6\times10^{-7}}\approx6\times10^{-4} \) M.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 9: The number of moles of hydroxide (\( \ce{OH-} \)) ions in 0.3 litre of 0.005 M \( \ce{Ba(OH)2} \) solution is
(a) 0.0050
(b) 0.0030
(c) 0.0015
(d) 0.0075
Show Answer & Explanation

Answer: (b) 0.0030

Explanation:
1. \( [OH^-]=2\times0.005=0.01 \) M.
2. Moles = 0.01 x 0.3 = 0.003.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 10: The pH of pure water or a neutral solution at 50 \( ^\circ C \) is (\( pK_w=13.26 \) at 50 \( ^\circ C \))
(a) 7.0
(b) 7.13
(c) 6.0
(d) 6.63
Show Answer & Explanation

Answer: (d) 6.63

Explanation:
1. In neutral water \( [H^+]=[OH^-] \), so \( pH=pK_w/2=13.26/2=6.63 \).

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 11: The pH of a 0.1 M solution of a weak acid HA is 4.50. It is neutralised with NaOH solution to decrease the acid content to half. The pH of the resulting solution is
(a) 4.50
(b) 8.00
(c) 9.00
(d) 7.00
Show Answer & Explanation

Answer: (b) 8.00

Explanation:
1. \( [H^+]=10^{-4.5} \), so \( K_a=(10^{-4.5})^2/0.1=10^{-8} \), \( pK_a=8 \).
2. At half neutralisation [salt] = [acid], so \( pH=pK_a=8.00 \).

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 12: A 0.1 N solution of an acid at room temperature has a degree of ionisation 0.1. The concentration of \( \ce{OH-} \) would be
(a) \( 10^{-12} \) M
(b) \( 10^{-11} \) M
(c) \( 10^{-9} \) M
(d) \( 10^{-2} \) M
Show Answer & Explanation

Answer: (a) \( 10^{-12} \) M

Explanation:
1. \( [H^+]=0.1\times0.1=10^{-2} \) M.
2. \( [OH^-]=10^{-14}/10^{-2}=10^{-12} \) M.

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 13: The pH of a solution containing 0.10 m sodium acetate and 0.03 m acetic acid (\( pK_a=4.57 \)) at 25 \( ^\circ C \) is
(a) 4.09
(b) 5.09
(c) 7.09
(d) 6.10
Show Answer & Explanation

Answer: (b) 5.09

Explanation:
1. \( pH=pK_a+\log(0.10/0.03)=4.57+0.52=5.09 \).

Teacher's Note:
1. Write the relevant expression (\( K_{sp} \), \( K_h \), pH or the Henderson equation) first, then substitute the data carefully.
2. Check that the answer is sensible: salts of strong bases are basic, salts of strong acids are acidic.

Question 14: For the reaction \( \ce{2HI <=> H2 + I2} \), if \( \alpha \) is the degree of dissociation of HI starting from 2 moles, the total number of moles at equilibrium is
(a) 2
(b) \( 2-\alpha \)
(c) 1
(d) \( 1-\alpha \)
Show Answer & Explanation

Answer: (a) 2

Explanation:
1. HI left = \( 2(1-\alpha) \), \( \ce{H2} \) = \( \alpha \), \( \ce{I2} \) = \( \alpha \).
2. Total = \( 2-2\alpha+2\alpha=2 \), since the moles do not change.

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 15: An aqueous solution of ammonium acetate is
(a) faintly acidic
(b) faintly basic
(c) fairly acidic
(d) almost neutral
Show Answer & Explanation

Answer: (d) almost neutral

Explanation:
1. \( K_a(CH_3COOH)\approx K_b(NH_3) \), so both ions hydrolyse equally.
2. The solution is almost neutral.

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 16: The strongest acid among the four listed is
(a) HCOOH
(b) \( \ce{CH3COOH} \)
(c) \( \ce{ClCH2COOH} \)
(d) \( \ce{FCH2COOH} \)
Show Answer & Explanation

Answer: (d) \( \ce{FCH2COOH} \)

Explanation:
1. Electron-withdrawing groups stabilise the carboxylate ion.
2. Fluorine is more electronegative than chlorine, so \( \ce{FCH2COOH} \) is the strongest.

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 17: The hydride ion \( \ce{H-} \) is a stronger base than the hydroxide ion \( \ce{OH-} \). Which reaction occurs when sodium hydride (NaH) is dissolved in water?
(a) \( \ce{H-(aq) + H2O -> H2O} \)
(b) \( \ce{H-(aq) + H2O(l) -> OH- + H2} \)
(c) \( \ce{H- + H2O -> no reaction} \)
(d) none of these
Show Answer & Explanation

Answer: (b) \( \ce{H-(aq) + H2O(l) -> OH- + H2} \)

Explanation:
1. \( \ce{H-} \) takes a proton from water, forming \( \ce{H2} \) gas and \( \ce{OH-} \).

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 18: The ionisation constant of phenol is higher than that of ethanol because
(a) the phenoxide ion is bulkier than the ethoxide ion
(b) the phenoxide ion is a stronger base than the ethoxide ion
(c) the phenoxide ion is stabilised through delocalisation
(d) the phenoxide ion is less stable than the ethoxide ion
Show Answer & Explanation

Answer: (c) the phenoxide ion is stabilised through delocalisation

Explanation:
1. The negative charge on the phenoxide ion is delocalised into the ring, which stabilises it.
2. A more stable conjugate base means a stronger acid.

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 19: Which one of the following is not a buffer solution?
(a) 0.8 M \( \ce{H2S} \) + 0.8 M KHS
(b) 2 M \( \ce{C6H5NH2} \) + 2 M \( \ce{C6H5NH3+Br-} \)
(c) 3 M \( \ce{H2CO3} \) + 3 M \( \ce{KHCO3} \)
(d) 0.05 M KClO4 + 0.05 M \( \ce{HClO4} \)
Show Answer & Explanation

Answer: (d) 0.05 M KClO4 + 0.05 M \( \ce{HClO4} \)

Explanation:
1. A buffer needs a weak acid (or base) and its conjugate pair.
2. \( \ce{HClO4} \) is a strong acid, so the last mixture is not a buffer.

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

Question 20: The increasing order of acidic character would be
(a) \( \ce{CH3COOH < H2SO4 < H2CO3} \)
(b) \( \ce{CH3COOH < H2CO3 < H2SO4} \)
(c) \( \ce{H2CO3 < CH3COOH < H2SO4} \)
(d) \( \ce{H2SO4 < H2CO3 < CH3COOH} \)
Show Answer & Explanation

Answer: (c) \( \ce{H2CO3 < CH3COOH < H2SO4} \)

Explanation:
1. \( pK_a \): \( \ce{H2CO3} \) about 6.4, \( \ce{CH3COOH} \) 4.76, \( \ce{H2SO4} \) strongly acidic.
2. Order: \( \ce{H2CO3 < CH3COOH < H2SO4} \).

Teacher's Note:
1. Recall the definition or trend involved and test each option against it one by one.
2. Compare with a standard example (for instance \( \ce{CH3COOH} \), \( \ce{NH4Cl} \) or \( \ce{NaCl} \)) to confirm your choice.

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