Question

What is the mass of 8.00 × 1022 molecules of NH3?

Answer 1

We find out the molar mass of NH₃.

atomic mass (N)=14 u
atomic mass (H)=1 u

atomic weight (NH₃)=14 u + 3(1u)=17 u

Therefore the molar mass of NH₃ will be: 17 g/mol
Then:
1 mol of water=18 g

2) We know that:
1 mol of any substance=6.022 * 10²³ particles.

3)We calculate the mass of 8.00 *10²² molecules

18 g of water----------------------------6.022*10²³ molecules
x---------------------------------------------8.00*10²² molecules
 
x=(18 g of water * 8.00*10²²  molecules) / 6.022 * 10²³ molecules=2.39 g

Answer: the mass of 8.00 *10²² molecules of NH₃ would be 2.39 g.

Answer 2

The mass of 8.00 × 10²² molecules of NH3 is 2.26g

HOW TO CALCULATE MASS:

• The mass of a substance can be calculated by multiplying the number of moles by its molar mass. That is;

mass (g) = no. of moles (mol) × molar mass (g/mol)

Molar mass of NH3 = 14 + 1(3) = 17g/mol

• However, we have to calculate the number of moles in NH3 by dividing the number of molecules in NH3 by Avogadro's number.

no. of moles in NH3 = 8.00 × 10²² ÷ 6.02 × 10²³

no. of moles = 8.00/6.02 × 10²²-²³

no. of moles = 1.33 × 10-¹mol or 0.133mol

Mass of NH3 = 0.133mol × 17g/mol

Mass of NH3 = 2.26g

• Therefore, the mass of 8.00 × 10²² molecules of NH3 is 2.26g

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