Question

How many grams of $NaOH$ must be added to make $200mL$ of a $1M$ $NaOH$ solution?

• A. $8g$
• B. $16g$
• C. $40g$
• D. $80g$

Answer 1

Answer: (A)

$8g$

First find the number of moles of $NaOH$ needed:
$200mL$ $NaOH$ $=$ $0.200L$
Number of moles are obtained by multiplying molarity with volume.
Number of moles $n$ $=1$ mol/L $\times 0.200$ mL $=0.200$ moles.
Next,
find the mass of $NaOH$ in $0.200$ moles of $NaOH$:
To obtain the mass of $NaOH$, the number of moles of $NaOH$ are multiplied with its molecular weight which is $40g/mol$.
The mass of $NaOH$ $=0.200$ mol $\times 40$ g/mol $=8$ g
Therefore $8$ gram of $NaOH$ is required.