Question

A sample of ammonia has a mass of 82.9 g. how many molecules are in this sample?

Answer 1

The chemical formula for ammonia is NH3. So first, you need to find the molar mass of ammonia (how many grams in one mole).
N=14g
H3=3g
So one mole of NH3 is 17 grams, you can divide 82.9 grams by 17 grams to find the number of molecules. The answer should be 4.876 moles (molecules) of ammonia. Hope this helps!

Answer 2

Answer: $29.37\times 10^{23}molecules$

Explanation: To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\textMolar mass}}$    

Given mass of ammonia $NH_3$ given = 82.9 g

Molar mass of ammonia $NH_3$ = 17 g/mol

Putting values in above equation, we get:

$\text{Moles of sodium}=\frac{82.9g}{17g/mol}=4.87mol$

According to Avogadro's law,

1 mole of any substance contains avogadro's number  $6.023\times 10^{23}$ of particles.

Thus 4.87 moles of ammonia contains=$\frac{6.023\times 10^{23}}{1}\times 4.87=29.37\times 10^{23}molecules$ of ammonia.