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Equilibrium · Question 26

JEE Main 2026 (Online) 22nd January Evening ShiftMCQMedium📈 Topic in 19% papers+4−1
1

Which of the following mixture gives a buffer solution with pH = 9.25 ? Given : pKb (NH4OH) = 4.75

  1. 0.5 M NH4OH (0.2 L) + 0.2 M HCl (0.5 L)
  2. 0.2 M NH4OH (0.5 L) + 0.1 M HCl (0.5 L)
  3. 0.2 M NH4OH (0.4 L) + 0.1 M HCl (1 L)
  4. 0.4 M NH4OH (1 L) + 0.1 M HCl (1 L)

Answer

(2) 0.2 M NH4OH (0.5 L) + 0.1 M HCl (0.5 L)

Solution

pOH = 14 - 9.25 = 4.75 = pKb

For a basic buffer: pOH = pKb + [NH4+][NH4OH]

we need moles of NH4Cl formed = moles of NH4OH left.

NH4OH + HCl NH4Cl + H2O

(A) NH4OH = 0.1 mol, HCl = 0.1 mol only NH4Cl remains (no buffer).

(B) NH4OH = 0.1 mol, HCl = 0.05 mol NH4OH left = 0.05 mol, NH4Cl = 0.05 mol

pOH = 4.75 + 1 = 4.75 pH = 9.25

(C) NH4OH = 0.08 mol, HCl = 0.1 mol HCl in excess (no buffer).

(D) NH4OH = 0.4 mol, HCl = 0.1 mol 0.3 mol base, 0.1 mol salt

pOH = 4.75 + 0.10.3 = 4.27 pH = 9.73

Answer: (2)

JEE Main 2026 (Online) 22nd January Evening Shift

Keep practising — Equilibrium

2

For the reaction, N2O4 2NO2, graph is plotted as shown below. Identify correct statements. [figure] Choose the correct answer from the options given below :

  1. C and E only
  2. D and E only
  3. A and D only
  4. B and C only
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3

The first and second ionization constants of H2X are 2.5 10-8 and 1.0 10-13 respectively. The concentration of X2- in 0.1 M H2X solution is 10-15 M. (Nearest Integer)

JEE Main 2026 (Online) 21st January Evening Shift
4

The equilibrium constant for decomposition of H2O(g) H2O(g) H2(g) + 12O2(g); G = 92.34 kJ mol-1 is 8.0 10-3 at 2300 K and total pressure at equilibrium is 1 bar. Under this condition, the degree of dissociation ( ) of water is 10-2 (nearest integer value). [Assume is negligible with respect to 1]

JEE Main 2025 (Online) 8th April Evening Shift
5

An aqueous solution of HCl with pH 1.0 is diluted by adding equal volume of water (ignoring dissociation of water). The pH of HCl solution would (Given 2 = 0.30)

  1. increase to 1.3
  2. reduce to 0.5
  3. increase to 2
  4. remain same
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6

One litre buffer solution was prepared by adding 0.10 mol each of NH3 and NH4Cl in deionised water. The change in pH on addition of 0.05 mol of HCl to the above solution is 10-2. (Nearest integer) Given : pKb of NH3 = 4.745 and 10 3 = 0.477

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7

The pH of a 0.01 M weak acid HX (Ka = 4 10-10) is found to be 5. Now the acid solution is diluted with excess of water so that the pH of the solution changes to 6. The new concentration of the diluted weak acid is given as x 10-4 M. The value of x is (nearest integer)

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8

x mg of Mg(OH)2 (molar mass = 58 g mol-1) is required to be dissolved in 1.0 L of water to produce a pH of 10.0 at 298 K. The value of x is mg. (Nearest integer) (Given : Mg(OH)2 is assumed to dissociate completely in H2O)

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9

In the following system, PCl5(g) PCl3(g) + Cl2(g) at equilibrium, upon addition of xenon gas at constant T & p, the concentration of

  1. PCl5, PCl3 & Cl2 remain constant
  2. PCl3 will increase
  3. Cl2 will decrease
  4. PCl5 will increase
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10

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below

  1. Statement I is true but Statement II is false
  2. Statement I is false but Statement II is true
  3. Both Statement I and Statement II are true
  4. Both Statement I and Statement II are false
JEE Main 2025 (Online) 3rd April Morning Shift
11

If equal volumes of AB2 and XY (both are salts) aqueous solutions are mixed, which of the following combination will give a precipitate of AY2 at 300 K ? (Given Ksp (at 300 K) for AY2 = 5.2 10-7)

  1. 2.0 10-4 M AB2, 0.8 10-3 M XY
  2. 2.0 10-2 M AB2, 2.0 10-2 M XY
  3. 1.5 10-4 M AB2, 1.5 10-3 M XY
  4. 3.6 10-3 M AB2, 5.0 10-4 M XY
JEE Main 2025 (Online) 2nd April Morning Shift

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