Question

100 mL of 0.1 M HCl is taken in a beaker and to it, 100 mL OF 0.1 M NaOH is added in steps of 2mL and the pH is continuously measured. Which of the following graphs correctly depicts the change in pH?
(A)

(B)

(C)

(D)

Answer 1

Hint: The pH determines the percentage of Hydrogen in a solution. The formula to calculate pH is \[{\rm{pH}} = - {\rm{log}}\left[ {{{\rm{H}}^{\rm{ + }}}} \right]\].

Complete Step by Step Solution:
Now, we will discuss the pH scale. This scale contains values from 0 to 14. The pH values<7 indicates the acidity of the solution, the pH value of 7 indicates a neutral solution and the pH value >17 indicates the basicity of the solution.

Here, at first, 100 mL HCl of 0.1 M is taken. At that time, the pH of the solution is less than 7, which means the solution is acidic. After that, the addition of NaOH to the acid solution occurs. That reduces the acidity of the solution. And a point comes when the solution becomes neutral, neither acidic nor basic. After that, further addition of NaOH causes an increase in the basicity of the solution.

Here, the graph in option (3) represents the correct change of pH on adding NaOH to the HCl. At the starting point, it shows the acidity of the solution. The point of pH 7 indicates the equivalence point. And after that, an increase in pH indicates the increase in the basicity of the solution.
Hence, option (c) is right.

Note: In titration, a solution (concentration is known) is mixed to a solution (unknown concentration) till the reaction reaches neutralisation. And this is indicated by the change of colour of the solution.