Question

Which of the following correctly represents $360$ g of water?
(i) $2$ moles of ${\text{H}}_2\text{O}$
(ii) $20$ moles of ${\text{H}}_2\text{O}$
(iii) $6.022\times {10}^{23}$ molecules of ${\text{H}}_2\text{O}$
(iv) $1.2044\times {10}^{25}$ molecules of ${\text{H}}_2\text{O}$

• A. (i) and (iii)
• B. (i) and (iii)
• C. (ii) and (iv)
• D. (ii) and (iii)

Answer 1

The correct option is C (ii) and (iv)

The gram molecular mass of water is 18 g.
Also, number of molecules in 1 mole of ${\text{H}}_2\text{O}$ = $6.022\times {10}^{23}$

We know that number of moles
= $\frac{\text{Mass in grams}}{\text{Gram molecular mass}}$

Number of moles of water in 360 g = $\frac{360}{18}=20$ mol.
Number of ${\text{H}}_2\text{O}$ molecules in 1 mole (18 g) = $6.022\times {10}^{23}$
So, number of molecules in 360 g of ${\text{H}}_2\text{O}$ = $\frac{360}{18}\times 6.022\times {10}^{23}$
= $1.2044\times {10}^{25}$ molecules of ${\text{H}}_2\text{O}$