Question

In order to prepare a buffer solution of pH 5.74, sodium acetate is added to acetic acid. If the concentration of acetic acid in the buffer is 1.0 M, the concentration of sodium acetate in the buffer is? (Round off to the nearest integer). [Given: \[p{k_a}\] (acetic acid) = 4.74]

Answer 1

Hint: Here, we have to apply the formula of pH in terms of logarithm after putting the values given to us in the question. Then, we will make the appropriate substitution and then take the antilog of it. Finally we will calculate the ratio of the salt and the concentration of both the acid and salt will be calculated.

Complete Step by Step Solution:
pH, or potential of hydrogen, is a metric for determining the acidity or basicity of aqueous or other liquid solutions. The term which is widely used in chemistry, refers to the values of the concentration of the hydrogen ion which ordinarily ranges between about 1 and 10−14 gram equivalents per litre in amounts ranging from 0 to 14. In pure water, it is neutral which is neither acidic nor basic. The concentration of the hydrogen ion is 10 −7 gram equivalents per litre, which is equal to a pH of 7. A solution with pH less than 7 is regarded as acidic. A solution with a pH greater than 7 is considered to be alkaline.

Formula for calculating the pH;
 pH = − log \[{k_a}\] + log \[([\dfrac{{salt}}{{acid}}])\]
As the value of pH and \[{k_a}\] are already given in question, so putting these values in the given formula:
 5.74 = − 4.74 + log \[([\dfrac{{salt}}{{acid}}])\]
 From the logarithmic property [a log b = log \[{b^a}\] ]
 5.74 = 4.74 + log \[([\dfrac{{salt}}{{acid}}])\]

Further solving,
 1 = log \[([\dfrac{{salt}}{{acid}}])\]
Taking antilog on both sides, we get:
 10/1 = [salt][acid]101= \[([\dfrac{{salt}}{{acid}}])\]
Hence, The ratio of salt to the acid will be 10:1.

Note: A pH metre is used to determine the pH, which transforms the difference in electromotive force into pH measurements. It is also called electrical potential or voltage between electrodes placed in the solution to be tested. Fundamentally, a pH metre consists of a voltmeter attached to a pH responsive electrode and a reference constant electrode and the readings are reflected in a digital screen.