How many milliliters of 0.2 M NaOH are required to exactly neutralize 40 milliliters of 0.1 M HCl?

A) 10

B) 20

C) 40

D) 80

Option B. 20mL

Explanation:

Step 1:

Data obtained from the question.

Volume of base (Vb) = ... ?

Molarity of base (Mb) = 0.2M

Volume of acid (Va) = 40mL

Molarity of acid (Ma) = 0.1M

Step 2:

The balanced equation for the reaction.

HCl + NaOH - > NaCl + H2O

From the balanced equation above, the following were obtained:

Mole ratio of the acid (nA) = 1

Mole ratio of the base (nB) = 1

Step 3:

Determination of the volume of base, NaOH needed for the reaction. This is illustrated below:

MaVa/MbVb = nA/nB

0.1 x 40 / 0.2 x Vb = 1

Cross multiply

0.2 x Vb = 0.1 x 40

Divide both side by 0.2

Vb = 0.1 x 40 / 0.2

Vb = 20mL

Therefore, the volume of the base is 20mL.