Chapter 14, Problem 56QAP

Interpretation Introduction

(a)

Interpretation:

The titration of the aqueous solution of amount 50.0mL contains 2.500g of the unknown base which is represented as RNH. The equivalence point of the titration is reached by the 0.925M of HCl of amount 59.90mL. In the titration of the second experiment 50.00mL of the unknown base is used which is identical to the base which is used in the previous experiment. In the solution of the second experiment, 0.925M of HCl of amount 29.95 mL is used. The pH value of the solution is 10.77 after the addition of the HCl.

The molar mass of the unknown base is to be determined.

Concept introduction:

The molarity of a solution is calculated as follows:

$\text{Molarity=}\frac{\text{number of moles of solute}}{\text{volume}}$

The number of moles can be calculated as follows:

$\text{number of moles=}\frac{\text{mass}}{\text{molar mass}}$

Interpretation Introduction

(b)

Interpretation:

The constant of equilibrium of the base, K_b is to be determined.

Concept introduction:

The formulas which will be used are-

At the mid-way equivalence point

$p{K}_a=-\log K_a$

The relation between equilibrium constant of acid and base -

$K_b=\frac{K_w}{K_a}$

Interpretation Introduction

(c)

Interpretation:

The constant equilibrium of acid K_a for RNH₂ + is to be determined.

Concept introduction:

The formulas which will be used is-

At the mid-way equivalence point

$p{K}_a=-\log K_a$