Question

How many grams are there in a $7.0$ mole sample of sodium hydroxide?

• A. $40.0g$
• B. $140.0g$
• C. $280.0g$
• D. $340.0g$
• E. $420.0g$

Answer 1

The correct option is C $280.0g$

The formula of sodium hydroxide is $NaOH$

Atomic weight of $Na$ = $23g/mol$

Atomic weight of $O$ = $16g/mol$

Atomic weight of $H$ = $1g/mol$

$\therefore$ molecular weight of $NaOH$ = atomic mass of $Na$ + atomic mass of $O$ + atomic mass of $H$

= $23+16+1=40g/mol$

Therefore, 1 mole of $NaOH=40g/mol$

7 moles of $NaOH=7mole\times 40g/mol=280g$

Hence, option $B$ is correct.