Question

What volume of $0.1$ M Ca(OH)${}_2$ will be required to neutralize $200$ mL of $0.2$ M H${}_2$SO${}_4$ using methyl orange indicator to change the colour from red (acidic medium) to yellow (basic medium)?

• A. $200$ mL
• B. $400$ mL
• C. $20$ mL
• D. $40$ mL

Answer 1

Answer: (A)

$200$ mL

Methyl orange indicator indicates the first step ionisation of $H_{2}S{O}_3$

$H_{3}S{O}_3\rightleftharpoons H^{⨁}+HS{O}_3^{⊝}$

$(n=1)(Ew=\frac{Mw}{1})(N=M\times 1)$

$Ca\left(OH\right)\equiv H_{2}S{O}_3$

$N_1\times V_1=N_2\times V_2$

$0.1\times 2\times V_1=0.2\times 1\times 2$

$V_1=200mL$

Hence, the correct option is $\text{A}$