Question

What is the normality of a NaOH solution if 25.7 mL of it react with 0.587 g of H2CrO4?

Answer 1

The equation for the reaction taking place is:

2NaOH + H2CrO4 ------------> Na2CrO4  +   2H2O

Hence, 2 parts of NaOH react with 1 part of chromic acid.

25.7 mL of NaOH solution reacts with 0.587 g of H2CrO4.

molar mass of H2CrO4 = 2 + 64 + 52 => 118 grams per mole.

=> 0.587/118 moles => 0.005 moles (approx.)

So, 1 part = 0.005 moles

2 parts =  2 x 0.005 => 0.01 moles

Hence, 2 parts of NaOH or 0.01 moles of NaOH is used.

So, in 25.7 ml of solution, 0.01 moles of NaOH is present.

25.7 mL = 0.0257 liters of solution

Molarity = (moles of NaOH) / (liters of solution)

=> 0.01 /0.0257

=>100/257

=>0.389 M (molar ) solution

Hence, the molarity of the solution is 0.389 M (molar).