10 ml of aqueous HCl is completely neutralised by 20 ml of 0.5 M aqueous NaOH solution in an experiment.The molarity of HCl is

Question

WHAT IS THE ANSWER?

Answer 1

The balanced chemical equation for this reaction shows that HCl and NaOH react on a 1:1 ratio:

HCl + NaOH --> NaCl + H₂O

 

This means that when the acid is completely neutralized by the base, there will be equal moles of both reactants present in the reaction mixture. So, to determine the molarity of HCl, we have to first determine the moles of HCl in the 10 mL sample by finding the moles of NaOH.

Given, 20 mL of 0.5 M NaOH, we can rearrange the molarity equation to find the number of moles of NaOH:

moles = Molarity x Liters

          = (0.5 M) x (0.02 L)

          = 0.01 moles

 

When we convert this to moles of HCl, it's stil 0.01 moles because, again they are present at the equivalence point in a 1:1 ratio:

0.01 moles NaOH x (1 moles HCl/1moles NaOH) = 0.01 moles HCl

 

The final step is to substitute the moles and volume (in liters!) of HCl into the molarity equation and solve:

Molarity = moles/Liters

             = 0.01 moles/0.01 liters

             = 1 Molarity