Which of the following does not form a buffer solution?
Which of the following does not form a buffer solution?
NH3+HCL (2:1 mole ratio)
CH3CO2H + NaOH (2:1 mole ratio)
$NaOH + CH_3COOH$ (1:1 mole ratio)
NH4Cl + NH3 (1:1 mole ratio)
The Correct Option is C
Solution and Explanation
To solve the problem, we need to identify which combination does not form a buffer solution.
1. Understanding Buffer Solutions:
A buffer solution resists changes in pH when small amounts of acid or base are added. Buffers are typically formed by:
- A weak acid and its salt with a strong base (e.g., CH₃COOH + CH₃COONa)
- A weak base and its salt with a strong acid (e.g., NH₃ + NH₄Cl)
The key is having a weak acid/base and its conjugate pair in proper proportions.
2. Analyze Each Option:
- Option 1: NH₃ + HCl (2:1 mole ratio)
NH₃ is a weak base and HCl is a strong acid. At a 2:1 ratio, not all NH₃ reacts with HCl, so some NH₃ and NH₄⁺ (from NH₄Cl) remain — this forms a buffer. - Option 2: CH₃COOH + NaOH (2:1 mole ratio)
Excess CH₃COOH remains after partial neutralization by NaOH, forming CH₃COONa and CH₃COOH — a buffer system. - Option 3: NaOH + CH₃COOH (1:1 mole ratio)
NaOH completely neutralizes CH₃COOH to form only CH₃COONa. No weak acid (CH₃COOH) remains, so this is not a buffer. - Option 4: NH₄Cl + NH₃ (1:1 mole ratio)
This is a classic weak base (NH₃) and its salt (NH₄Cl) — it forms a buffer.
Final Answer:
The correct answer is NaOH + CH₃COOH (1:1 mole ratio) because it does not form a buffer solution.
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Concepts Used:
Law of Chemical Equilibrium
Law of Chemical Equilibrium states that at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants each raised to a power equal to the corresponding stoichiometric coefficients as represented by the balanced chemical equation.
Let us consider a general reversible reaction;
A+B ↔ C+D
After some time, there is a reduction in reactants A and B and an accumulation of the products C and D. As a result, the rate of the forward reaction decreases and that of backward reaction increases.
Eventually, the two reactions occur at the same rate and a state of equilibrium is attained.
By applying the Law of Mass Action;
The rate of forward reaction;
Rf = Kf [A]a [B]b
The rate of backward reaction;
Rb = Kb [C]c [D]d
Where,
[A], [B], [C] and [D] are the concentrations of A, B, C and D at equilibrium respectively.
a, b, c, and d are the stoichiometric coefficients of A, B, C and D respectively.
Kf and Kb are the rate constants of forward and backward reactions.
However, at equilibrium,
Rate of forward reaction = Rate of backward reaction.
Kc is called the equilibrium constant expressed in terms of molar concentrations.
The above equation is known as the equation of Law of Chemical Equilibrium.