Question

A solution of $10M$ $NaOH$ was used to prepare $2L$ of $0.5M$ $NaOH$. How many $mL$ of the original $NaOH$ solution are needed?

• A. $10mL$
• B. $100mL$
• C. $1000mL$
• D. $200mL$
• E. $2000mL$

Answer 1

Answer: (B)

$100mL$

From reaction,

$M_1{V}_1=M_2{V}_2$

$V_1=\frac{M_2\times V_2}{M_1}$

$V_1=\frac{0.5M\times 2L}{10M}$

$V_1=0.1L$

$V_1=0.1L\times 1000mL/L$

$V_1=100mL$