Question

A 5.00-ml sample of an h3po4 solution of unknown concentration is titrated with a 0.1090 m naoh solu- tion. a volume of 7.12 ml of the naoh solution was required to reach the equivalence point. what is the concentration of the unknown h3po4 solution?

Answer 1

The concentration of unknown H3PO4 solution is 0.052 M

calculation

step 1: write the balanced molecular equation

3NaOH + H3PO4→ Na3PO4 +3H2O

step 2: find the moles of NaOH

moles = molarity x volume in liters

volume in liters = 7.12 ml /1000 = 0.00712 L

molarity = 0.1090 M = 0.1090 mol/l

moles is therefore = 0.1090 mol/L x 0.00712 L =0.00078 moles

step 3: use the mole ratio to determine the moles of H3PO4

H3Po4: NaOH is 3:1 therefore the moles of H3PO4

= 0.00078 x1/3 =0.00026 moles

Step 4: calculate the molarity of H3PO4

molarity = moles/volume in liters

volume in liters = 5.00 / 1000 =0.005 L

molarity is= 0.00026/0.005=0.052 M