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# A sample of chalk $(CaCO_3)$ is contaminated with calcium sulphate $(CaSO_4)$ 1gm of the solid mixture is dissolved in 230ml of N/10 HCl; 40ml of N/10 NaOH is required to neutralize the excess of acid.Find the percentage of chalk in the mixture.

$(a)\;95\%\qquad(b)\;92\%\qquad(c)\;93\%\qquad(d)\;91\%$

Can you answer this question?

Volume of HCl used against $CaCO_3$ is not given.
Excess of HCl is neutralized by NaOH
$N_1V_1=N_2V_2$
$\Rightarrow \big(\large\frac{1}{10}\big)$$\times V_1=\big(\large\frac{1}{10}\big)$$\times 40$
$V_1=40ml$=Volume of excess HCl
Volume of HCl used for $CaCO_3=230-40=190cc$
Meq of HCl=Meq of $CaCO_3$
$\large\frac{1}{10}$$\times 190=\large\frac{g}{E}$$\times 1000$
g=0.95=95% Pure carbonate.
Hence (a) is the correct answer.
answered Jan 8, 2014