Question

A 5.40 mL sample of an H3PO4 solution of unknown concentration is titrated with a 5.000×10−2 M NaOH solution. A volume of 7.02 mL of the NaOH solution was required to reach the equivalence point.
What is the concentration of the unknown H3PO4 solution?
Express your answer using four significant figures.

Answer 1

Answer:

0.02167 M

Explanation:

At first we need balanced equation

3NaOH + H3PO4 = Na3PO4 + 3H2O

This means for every 3 moles of NaOH we have 1mol of H3PO4.

At equivalence point we have equal moles of both titrant and analyte in our case H3PO4 and NaOH. start by finding the moles of NaOH

Molarity= moles/Litres

0.05= y/0.00702

x= 3.51x10^-4 moles

But keep in mind the balanced equation that says for every 3 moles of NaOH we have 1mol of H3PO4

so we divide by 3 moles to get moles of h3po4.

3.51x10^-4 moles NaOH x 1mol of H3Po4/3moles of NaOH

= 1.17x10^-4 moles of H3PO4

to find the molarity then use the forumla above

M = moles/litres

= 1.17x10^-4/0.0054

= 0.02167 M