Question

The equilibrium for the reaction between (CH₃)₂NH , a weak base, and water is represented by the equation below. The table shows the pHpH of three solutions of (CH₃)₂NH(aq) at 25°C

(CH₃)₂NH(aq)+H2O(l)⇄(CH₃)₂NH²⁺(aq)+OH-(aq) Kb=5.4×10⁻⁴ at 25°

[(CH₃)₂NH] pH at25°C
0.050 11.69
0.10 11.85
0.20 12.01


Based on the information given, which of the following is true?



A. Solutions with a higher concentration of (CH₃)₂NH have a higher pOH because to reach equilibrium a smaller amount of the conjugate acid (CH₃)₂NH²⁺ is produced.
B. Solutions with a higher concentration of (CH₃)₂NH have a higher pOH because to reach equilibrium more OH⁻is produced.
C. Solutions with a higher concentration of (CH₃)₂NH have a higher pH because to reach equilibrium a smaller amount of the conjugate acid (CH₃)₂NH²⁺ is produced.
D. Solutions with a higher concentration of (CH₃)₂NH have a higher pH because to reach equilibrium more OH⁻is produced.

Answer 1

The correct answer is that solutions with a higher concentration of (CH₃)₂NH have a higher pH because more OH- is produced to reach equilibrium, leading to increased basicity of the solution. Option D is the correct answer.

Step-by-step explanation:

The question is related to the equilibrium established when a weak base, (CH₃)₂NH, reacts with water. As the base reacts, it produces hydroxide ions (OH-) and its conjugate acid, (CH₃)₂NH²+. The provided data shows three solutions of varying concentrations of (CH₃)₂NH and their respective pH levels at 25°C. Understanding the relationship between concentration and pH in this context is key to answering the question.

According to the information and principles of acid-base equilibrium, solutions with a higher concentration of (CH₃)₂NH will have more OH- ions because a higher concentration of base will react with water to produce more OH- ions to reach equilibrium. This will lead to a higher pH value, not a higher pOH. Thus, we can state that the correct answer is:

D. Solutions with a higher concentration of (CH₃)₂NH have a higher pH because to reach equilibrium more OH⁻ is produced.