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