Quantitative Chemistry: Calculating Mass of a Number of Moles (DONE)

Question 1

What’s the equation used to calculate the mass of a number of moles?

Answer 1

The equation used to calculate the mass of a number of moles is:

Mass (g) = number of moles x relative formula mass Mr

Question 2

Calculate the mass of four moles of sodium chloride (NaCl)

NaCl

Ar Na = 23
Ar Cl = 35.5

Answer 2

1 x 23 = 23
1 x 35.5 = 35.5
35.5 + 23 = 58.5

The relative formula mass (Mr) is 58.5

Mass (g) = number of moles x relative formula mass

234 = 4 x 58.5

The total mass of 4 moles of sodium chloride is 234g.

Question 3

Calculate the mass of three moles of potassium oxide (K↓2O)

K↓2O

Ar K = 39
Ar O = 16

Answer 3

2 x 39 = 78
1 x 16 = 16
78 + 16 = 94

The relative formula mass is 94.

mass = 3 x 94

The mass of three moles of potassium oxide is 282g.

Question 4

Calculate the mass of 0.1 moles of caesium nitrate

CsNO↓3

Ar Cs = 133
Ar N = 14
Ar O = 16

Answer 4

1 x 133 = 133
1 x 14 = 14
3 x 16 = 48
133 + 14 + 38 = 195

185 x 0.1 = 19.5

Mass of 0.1 moles of caesium nitrate is 19.5g

Question 5

How can you calculate the mass of a number of moles?

Answer 5

By using the equation used to calculate the mass of a number of moles:

Mass (g) = number of moles x relative formula mass Mr

Question 6

Calculate the mass of 5 moles of copper sulphate.

CuSO↓4

Cu = 63.5
S = 32
O = 16

Answer 6

Mass (g) = number of moles x relative formula mass

63.5 x 1 = 63.5
32 x 1 = 32
16 x 4 = 64
63.5 + 32 + 48 = 159.5

Mr = 159.5

5 x 159.5 = 797.5

The mass of 5 moles of copper sulphate is 797.5g.