Question

A chemistry student weighs out 0.09666 g of phosphoric acid (H3PO4), a triprotic acid, into a 250.volumetric flask and dilutes to the mark with distilled water. He plans to titrate the acid with 0.2000 M NaoH solution. Calculate the volume of NaoH solution the student will need to add to reach the final equivalence point. Round your answer to 3 significant digits.

Answer 1

Answer: 14.62 ml

Step-by-step explanation:

Molarity is defined as the number of moles of solute dissolved per liter of the solution.

`Molarity=(n* 1000)/(V_s)`

where,

n= moles of solute

`V_s` = volume of solution in ml = 250 ml

`{\text {moles of solute}=\frac{\text {given mass}}{\text {molar mass}}=(0.09666g)/(98g/mol)=9.9* 10^(-4)`

Now put all the given values in the formula of molarity, we get

`Molarity=(9.9* 10^(-4)* 1000)/(250ml)`

`Molarity=3.9* 10^(-3)M`

To calculate the volume of base, we use the equation given by neutralization reaction:

`n_1M_1V_1=n_2M_2V_2`

where,

`n_1,M_1\text{ and }V_1` are the n-factor, molarity and volume of acid which is
`H_3PO_4`

`n_2,M_2\text{ and }V_2` are the n-factor, molarity and volume of base which is NaOH.

We are given:

`n_1=3\\M_1=3.9* 10^(-3)M\\V_1=250mL\\n_2=1\\M_2=0.2000M\\V_2=?`

Putting values in above equation, we get:

`3* 3.9* 10^(-3)* 250=1* 0.2000* V_2\\\\V_2=14.62ml`

Thus the volume of NaOH solution the student will need to add to reach the final equivalence point is 14.62 ml