Question

Vinegar is a chemical used in cooking, cleaning and other common experiences. A 0.1 M solution of vinegar in water has a [H+] of about 1.3 × 10–3. (You may prefer to think of the hydronium ion concentration, [H3O+], as 1.3 × 10–3.)
A. Write the formula for the calculation of pH, and then show each step as you calculate the pH of a 0.1 M solution of vinegar.

B. Is vinegar an acid or a base? Explain how you know.

Answer 1

Answer: a) pH of a 0.1 M vinegar solution is 2.9

b) It is an acid as pH is less than 7

Explanation:

pH or pOH is the measure of acidity or alkalinity of a solution.

pH is calculated by taking negative logarithm of hydrogen ion concentration.

Acids have pH ranging from 1 to 6.9, bases have pH ranging from 7.1 to 14 and neutral solutions have pH equal to 7.

As vinegar is  a weak acid, its dissociation is represented as;

$CH_3COOH\rightleftharpoons H^+CH-3COO^-$

   cM              0             0

$c-c\alpha$        $c\alpha$          $c\alpha$  

So dissociation constant will be:

$K_a=\frac{(c\alpha)^{2}}{c-c\alpha}$

Give c= 0.1 M

$[H^+]=c\times \alpha$

$[H^+]=0.1\times \alpha$

$1.3\times 10^{-3}=0.1\times \alpha$

$\alpha=0.013$

Also $pH=-log[H^+]$

$pH=-log[1.3\times 10^{-3}]=2.9$

Thus pH of a 0.1 M vinegar solution is 2.9

As pH is less than 7,  it is an acid.