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

Explanation:

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

$Molarity=\frac{n\times 1000}{V_s}$

where,

n= moles of solute  

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

${\text {moles of solute}=\frac{\text {given mass}}{\text {molar mass}}=\frac{0.09666g}{98g/mol}=9.9\times 10^{-4}$

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

$Molarity=\frac{9.9\times 10^{-4}\times 1000}{250ml}$

$Molarity=3.9\times 10^{-3}M$

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:

$n_1=3\\M_1=3.9\times 10^{-3}M\\V_1=250mL\\n_2=1\\M_2=0.2000M\\V_2=?$

Putting values in above equation, we get:

$3\times 3.9\times 10^{-3}\times 250=1\times 0.2000\times V_2\\\\V_2=14.62ml$

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