# A buffer is made by dissolving 12.5 g of sodium dihydrogen phosphate, NaH 2 PO 4 , and 15.0 g of disodium hydrogen phosphate, Na 2 HPO 4 , in a liter of solution. What is the pH of the buffer?

### General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
Publisher: Cengage Learning
ISBN: 9781305580343

### General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
Publisher: Cengage Learning
ISBN: 9781305580343

#### Solutions

Chapter
Section
Chapter 16, Problem 16.104QP
Textbook Problem

## A buffer is made by dissolving 12.5 g of sodium dihydrogen phosphate, NaH2PO4, and 15.0 g of disodium hydrogen phosphate, Na2HPO4, in a liter of solution. What is the pH of the buffer?

Expert Solution
Interpretation Introduction

Interpretation:

The pH of the given buffer which is made by dissolving 12.5 g of sodium dihydrogen phosphate and 15.0 g of disodium hydrogen phosphate in a liter of solution has to be calculated.

Concept Introdution:

pH definition:

The pH of a solution is defined as the negative base-10 logarithm of the hydronium ion [H3O+] concentration.

pH=-log[H3O+]

### Explanation of Solution

To Calculate: The pH of the given buffer which is made by dissolving 12.5 g of sodium dihydrogen phosphate and 15.0 g of disodium hydrogen phosphate in a liter of solution

Given data:

A buffer is made by dissolving 12.5 g of sodium dihydrogen phosphate, NaH2PO4 and 15.0 g of disodium hydrogen phosphate, Na2HPO4 in a liter of solution

pH calculation:

The concentration of dihydrogen phosphate ion (H2PO4-) is:

Conc. of H2PO4- =12.5 g NaH2PO4120.0 g/mol1.00 L =0.1042 M H2PO4-

The concentration of hydrogen phosphate ion (HPO42-) is:

Conc. of HPO42- =15.0 g Na2HPO4142.0 g/mol1.00 L =0.1056 M HPO42

Construct an equilibrium table with x as unknown concentration

 H2PO4-     +   H2O ⇌   H3O+     +     HPO42− Initial (M) 0

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