The correct order of value of pk_b the following amines is (i)`C_2H_5NH_2`(ii)`(C_2H_5)_2NH`(iii)`(C_2H_5)_3N`

Options

A. `(i)gt(ii)gt(iii)`
B. `(iii)gt(ii)gt(i)`
C. `(ii)gt(i)gt(iii)`
D. `(i)gt(iii)gt(ii)`

Answer

To determine the correct order of the values of pK_b for the given amines (i) C₂H₅NH₂ (ethylamine), (ii) (C₂H₅)₂NH (diethylamine), and (iii) (C₂H₅)₃N (triethylamine), we need to analyze their basicity.

### Step 1: Understand the relationship between pK_b and basicity
- pK_b is the negative logarithm of the base dissociation constant (K_b). A lower pK_b value indicates a stronger base, meaning that the amine can accept protons more readily.

### Step 2: Compare the basicity of the amines
- **Ethylamine (C₂H₅NH₂)**: This is a primary amine. It has one ethyl group attached to the nitrogen, which can donate electron density to the nitrogen, enhancing its basicity.
- **Diethylamine ((C₂H₅)₂NH)**: This is a secondary amine. It has two ethyl groups attached to the nitrogen. The presence of two electron-donating groups increases the electron density on the nitrogen even more than in ethylamine, making it a stronger base.
- **Triethylamine ((C₂H₅)₃N)**: This is a tertiary amine. It has three ethyl groups attached to the nitrogen. While it has the highest number of electron-donating groups, the steric hindrance around the nitrogen can make it less available to accept protons compared to the secondary amine.

### Step 3: Determine the order of K_b values
- In aqueous solution, the order of basicity (and thus K_b) is:
- Diethylamine > Ethylamine > Triethylamine
- This means:
- K_b for diethylamine > K_b for ethylamine > K_b for triethylamine

### Step 4: Convert K_b order to pK_b order
- Since pK_b is inversely related to K_b, the order of pK_b values will be the opposite:
- pK_b for diethylamine < pK_b for ethylamine < pK_b for triethylamine

### Final Order of pK_b Values
Thus, the correct order of pK_b values for the given amines is:
- (ii) (C₂H₅)₂NH < (i) C₂H₅NH₂ < (iii) (C₂H₅)₃N

### Summary
The correct order of pK_b values is:
1. (C₂H₅)₂NH (diethylamine) - lowest pK_b (strongest base)
2. C₂H₅NH₂ (ethylamine) - middle pK_b
3. (C₂H₅)₃N (triethylamine) - highest pK_b (weakest base)