Acid–base Equilibria
For the weak acid HA (Ka = 4.0×10⁻⁷), which expression best gives [H+] in a solution of initial concentration C where C ≫ Ka?
Select the correct option:
Solution
[H+] ≈ √(Ka·C)
- Dissociation: HA⇌H++A−.
- Equation: Ka=[HA][H+][A−].
- Simplification: Since HA is a weak acid, [H+]=[A−]=x. Also, assuming very low dissociation (C≫Ka), [HA]≈C.
- Substituting: Ka=Cx2.
- Solving: x2=Ka⋅C⟹x=Ka⋅C.
- Result: [H+]≈Ka⋅C is the standard approximation for weak acid concentrations.
🔒 Solution Hidden from View
Submit your answer to unlock the detailed step-by-step solution.
More acid–base equilibria Practice Questions
The conjugate base of HSO₄⁻ is:
The conjugate base of HSO₄⁻ is:
Calculate [H+] (in mol L⁻¹) after mixing 25 mL of 0.040 M HCl with 75 mL of water (assume volumes ad...
Calculate [H+] (in mol L⁻¹) after mixing 25 mL of 0.040 M HCl with 75 mL of water (assume volumes ad...
Which change increases the pH of an acetic acid/sodium acetate buffer the most?
Which change increases the pH of an acetic acid/sodium acetate buffer the most?
The percent dissociation of a 1.0×10⁻³ M solution of a weak monoprotic acid (Ka = 1.0×10⁻⁵) is appro...
The percent dissociation of a 1.0×10⁻³ M solution of a weak monoprotic acid (Ka = 1.0×10⁻⁵) is appro...
The conjugate acid of (CH3)3 N is:
The conjugate acid of (CH3)3 N is:
Which factor most strongly determines whether an amphoteric species acts as an acid or a base in wat...
Which factor most strongly determines whether an amphoteric species acts as an acid or a base in wat...
About This Question
- Subject
- chemistry
- Chapter
- equilibrium
- Topic
- acid–base equilibria
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
[H+] ≈ √(Ka·C)
- Dissociation: HA⇌H++A−.
- Equation: Ka=[HA][H+][A−].
- Simplification: Since HA is a weak acid, [H+]=[A−]=x. Also, assuming very low dissociation (C≫Ka), [HA]≈C.
- Substituting: Ka=Cx2.
- Solving: x2=Ka⋅C⟹x=Ka⋅C.
- Result: [H+]≈Ka⋅C is the standard approximation for weak acid concentrations.
This medium difficulty chemistry question is from the chapter equilibrium, covering the topic of acid–base equilibria. It appeared in the 2025 exam.
Looking for more practice? Explore all chemistry questions or browse equilibrium questions on RankGuru.