Which of the following occurs when HCl is added to a budder containing (CH3)3N and (CH3)3NH+?
The concentraion of (CH3)3N will increase.
The concentraion of (CH3)3NH+ will increase
The concentraion of (CH3)3N will decrease.
The concentraion of (CH3)3NH+ will decrease.
The correct answer and explanation is :
Correct Answer:
The concentration of (CH₃)₃NH⁺ will increase.
Explanation:
A buffer solution containing (CH₃)₃N (trimethylamine) and its conjugate acid (CH₃)₃NH⁺ (trimethylammonium ion) follows the principles of the Henderson-Hasselbalch equation, which describes how a buffer resists changes in pH upon the addition of an acid or base.
Step 1: Understanding the Buffer Components
- (CH₃)₃N (Trimethylamine) is a weak base.
- (CH₃)₃NH⁺ (Trimethylammonium ion) is its conjugate acid.
- The buffer maintains pH by shifting equilibrium:
[
(CH₃)₃N + H^+ \rightleftharpoons (CH₃)₃NH^+
]
Step 2: Effect of Adding HCl
Hydrochloric acid (HCl) is a strong acid and dissociates completely into H⁺ and Cl⁻ in solution. When HCl is added to the buffer:
- The excess H⁺ ions react with (CH₃)₃N to form (CH₃)₃NH⁺ (conjugate acid).
- This shifts the equilibrium to the right, increasing the concentration of (CH₃)₃NH⁺ while decreasing the concentration of (CH₃)₃N.
Step 3: Answering the Question
- The concentration of (CH₃)₃NH⁺ will increase ✅ (correct)
- The concentration of (CH₃)₃N will decrease (also true, but not listed as the main answer choice)
- The concentration of (CH₃)₃N will increase ❌ (incorrect; it reacts with H⁺)
- The concentration of (CH₃)₃NH⁺ will decrease ❌ (incorrect; it forms more of this ion)
Thus, the correct answer is: The concentration of (CH₃)₃NH⁺ will increase because the added HCl shifts the equilibrium to form more of the conjugate acid.