Question

Find the number of molecules in 1.8 g of ${\mathrm{H}}_2\mathrm{O}.$

Answer 1

.Step 1. Given,

weight of ${\mathrm{H}}_2\mathrm{O}$ (water) is 1.8 g

Step 2:Calculating number of moles

Applying formula,

Moles $=\frac{\mathrm{weight}}{\mathrm{Molecular}\mathrm{weight}}$

$=\frac{1.8}{18}$

$=0.1\mathrm{mole}.$

Step 3 then calculating number of Molecules.

Applying formula

number of molecules $=\mathrm{Moles}\times {\mathrm{N}}_{\mathrm{A}}$

$=0.1\times 6.023\times {10}^{23}$

$=6.023\times {10}^{22}$

Therefore,number of molecules in 1.8 g of ${\mathrm{H}}_2\mathrm{O}$ $=6.023\times {10}^{22}$molecules.