Question

A sample of ammonia has a mass of $51.1g$. How many molecules are in this sample?

• A. $1.8\times {10}^{23}$ molecules
• B. $3.6\times {10}^{23}$ molecules
• C. $9.1\times {10}^{23}$ molecules
• D. $1.8\times {10}^{24}$ molecules

Answer 1

The correct option is D $1.8\times {10}^{24}$ molecules

given mass of ammonia is 51.1g

in this number of moles = $\frac{51.1}{17.031}$ = 18

Now in a mole, there are Na molecules, this is known $6.023\times {10}^{23}$

since 1 mol = $6.023\times {10}^{23}$

thus,

18 mol = $18\times 6.023\times {10}^{23}$ = $1.8\times {10}^{24}$