JEE Main · Chemistry ↓ Falling

Equilibrium appeared 36 times across 3 years — 4.2% of Chemistry. This question is from Buffer Solution pH Calculation.

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

Solution & Explanation

Related Formula
pOH = 14 - pH = 14 - 9.25 = 4.75 pOH = pKb + [Salt][Base]
Core Logic

Step 1: Determine condition for pOH = 4.75:

4.75 = 4.75 + [Salt][Base] [Salt][Base] = 0 [Salt] = [Base]

Step 2: Test Option (2):

Initial millimoles of NH₄OH = 0.2 × 500 = 100 mmol Initial millimoles of HCl = 0.1 × 500 = 50 mmol Millimoles of NH₄Cl formed = 50 mmol Millimoles of NH₄OH remaining = 100 - 50 = 50 mmol

Since [Salt] = [Base], pOH = pKb = 4.75 and pH = 9.25.

Pattern Recognition

Sees: Basic buffer when pH = 14 - pKb. Shortcut: Requires millimoles of remaining weak base to equal millimoles of formed conjugate salt (i.e. acid amount must be exactly half of base amount).

Chapter Mix

Class 11 Chemistry: Equilibrium

Reference Study Guides

Equilibrium

More Equilibrium Previous-Year Questions — Page 8

Q62 jee_main_2024_31_jan_morning Equilibrium Constant
For the given reaction, choose the correct expression of KC from the following :- Fe(aq)³⁺ + SCN(aq)⁻ leftharpoons (FeSCN)(aq)²⁺
  • A. KC = [FeSCN²⁺][Fe³⁺][SCN⁻]
  • B. KC = [Fe³⁺][SCN⁻][FeSCN²⁺]
  • C. KC = [FeSCN²⁺][Fe³⁺]²[SCN⁻]²
  • D. KC = [FeSCN²⁺]²[Fe³⁺][SCN⁻]

Solution

Related Formula
KC = [Products][Reactants]
Core Logic
KC = Products ion conc.Reactants ion conc. KC = [FeSCN²⁺][Fe³⁺][SCN⁻]
Chapter Mix

Class 11 Chemistry: Equilibrium

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JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)