Which set of solutes will form a buffer when dissolved in water to make 1 litter of solution ?
Correct answer: D. 0.4 mole of NH3 with 0.2 mole of HCI
- A. 0.0002M HCI
- B. 0.2 mole of NaCI with 0.2 mole of HNO3
- C. 0.4 mole of CH3COOH with 0.4 mole of NaOH
- D. 0.4 mole of NH3 with 0.2 mole of HCI
Explanation
A buffer contains a weak base and its conjugate acid. HCl neutralizes half of the 0.4 mol NH3, leaving 0.2 mol NH3 and producing 0.2 mol NH4Cl in 1 L, so both NH3 and NH4+ are present. The likely trap is option c, where equal amounts of CH3COOH and NaOH completely neutralize each other, leaving acetate but no weak acid.
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About Buffer Solutions
Buffer solutions resist changes in pH when small amounts of acid or base are added, using a weak acid and its conjugate base or a weak base and its conjugate acid. Work includes buffer action, the common-ion effect, Henderson-Hasselbalch calculations, buffer capacity, and the difference between acidic and basic buffers.
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