Question

Molarity of $720gm$ of pure water is:

• A. $40M$
• B. $4M$
• C. $55.5M$
• D. None of these

Answer 1

The correct option is C $55.5M$

Molecular weight of water = 18 gm

Given weight of water = 720 gm

As we know that,

No. of moles $=\frac{\text{Given weight}}{\text{Molecular weight}}$

$\therefore$ No. of moles of water $=\frac{720}{18}=40$

As we know that,

density of water $=1gm/mL$

$\therefore density=\frac{mass}{volume}$

$\Rightarrow Volume=density\times mass$

$\Rightarrow volume=1\times 720=720mL=\frac{720}{1000}$

$\therefore Molality=\frac{\text{No. of moles}}{\text{Volume (in L)}}=\frac{40}{\left(\frac{720}{1000}\right)}=55.55M$

Hence, the correct option is $C$