Question

A solution contain ${Na}_2{CO}_3$ and $NaHC{O}_3$. 10 ml of this solution required 2.5 ml of 0.1 M $H_2{SO}_4$ for neutralization using phenolphthalein as indicator. Methyl orange is then added when a further 2.5 ml of 0.2 M $H_2{SO}_4$ was required. The amount of ${Na}_2{CO}_3$ and $NaHC{O}_3$ in 1 litre of the solution is ?

• A. 5.3 g and 4.2 g
• B. 3.3 g and 6.2 g
• C. 4.2 g and 5.3 g
• D. 6.2 g and 3.3 g

Answer 1

The correct option is A 5.3 g and 4.2 g

$x$ moles ${Na}_2{CO}_3$, $y$ moles of ${NaHCO}_3$

$\left(x\right)=2.5\times 0.1\times 2=0.5$ millimole

$x+y=2.5\times 0.2\times 2=1$ millimole

$y=0.5$ milli mole, $x=0.5$ milli mole in $10ml$

Hence $1$ lit $y=50$ millimole, $x=50$ millimole

${Na}_2{CO}_3=50\times {10}^{-3}\times 106=5.3g$

${NaHCO}_3=50\times {10}^{-3}\times 84=4.29$