# Question 24ab3

May 24, 2016

Choice A)

#### Explanation:

The equivalence point is reached when the indicator is changed colour.

Some students might be mistaken by choosing the choice B). In fact, the equivalence point is reached when the number of mole of ${H}^{+}$ is equal to the number of mole of $O {H}^{-}$, which is not necessary means that the number of mole of acid is equal the number of mole of base.

For example, consider the sulphuric acid (${H}_{2} S {O}_{4}$) that is being titrated by sodium hydroxide ($N a O H$).

In this case, ${n}_{{H}_{2} S {O}_{4}} = 2 \times {n}_{{H}^{+}}$ and ${n}_{N a O H} = {n}_{O {H}^{-}}$ therefore, when the equivalence point is reached,

n_(H^(+))=n_(OH^(-)#

$\implies {n}_{{H}_{2} S {O}_{4}} = 2 \times {n}_{N a O H}$

thus, the number of mole of acid is equal to twice the number of mole of base added.

Here is a video that explains titration with more details:
Lab Demonstration | Acid - Base Titration.