Question

If is found that 24.68 mL of .1165 M NaOH is needed to titrate .2931 g of an unknown acid to the phenolphthalein end point. Calculate the equivlanet mass of the acid.

Answer 1

Answer: The equivalent mass of the acid is 83.16 grams

Explanation:

To calculate the number of moles for given molarity, we use the equation:

$\text{Moles of solute}={\text{Molarity of the solution}}\times{\text{Volume of solution (in L)}}$  

Molarity of $NaOH$ solution = 0.1165 M

Volume of $NaOH$ solution = 24.68 mL = 0.02468 L

Putting values in equation 1, we get:

$\text{Moles of} NaOH={0.1165M}\times{0.02468L}=2.875\times 10^{-3}moles=2.875\times 10^{-3}geq$    

( as acidity of NaOH is 1)

For end point:  gram equivalents of acid =  gram equivalents of base = $2.875\times 10^{-3}$

Mass of acid=$gram equivalents\times {\text {Equivalent mass}}$

$0.2391=2.875\times 10^{-3}\times {\text {Equivalent mass}}$

${\text {Equivalent mass}}=83.16g$

Thus equivalent mass of the acid is 83.16 grams