The Mole Part 2

CALCULATIONS – MASS TO MOLES

m
n=
M
Where n = number of moles,
m = mass of substance in grams,
M = molar mass of the substance in grams.

EXAMPLES
1. Calculate the number of moles of sodium chloride contained in 100.0 g of this substance.

M (NaCl) = 23.0 + 58.5 = 58.5 g mol – 1

m 100
n (NaCl) = = = 1.71 mol
M 58.5

2. Calculate the number of moles of sulfuric acid in 240 g of this substance.

M (H2SO4) = (1.0 x 2) + 32.1 + (16.0 x 4) = 98.1 g mol – 1

m 240
n (H2SO4) = = = 2.45 mol
M 98.1

CALCULATIONS – MOLES TO MASS

We can rearrange the first formula to convert moles to mass.

m
n= becomes m = n x M
M

where m = mass of the substance in grams

EXAMPLES

1. Calculate the mass of 5.0 moles of glucose (C6H12O6)

M (C6H12O6) = (6 x 12.0) + (2 x 1.0) + (6 x 16.0) = 180 g mol – 1

m (C6H12O6) = n x M = 5 x 180 = 900 g

2. Calculate the mass of 0.435 moles of ammonium carbonate.

M ((NH4)2CO3) = (2 x 14.0) + (8 x 1.0) + (1 x 12.0) + (3 x 16.0) = 96 g mol – 1

QUESTIONS
m
1. Calculate the number of moles of (by using n = )
M

(a) Calcium in 80.2 g of calcium (Ca)

2 mol

(b) Carbon dioxide in 8.8 g of carbon dioxide (CO2)

0.2 mol

(c) Hydrochloric acid in 10.0 g of hydrochloric acid (HCl)

0.27 mol

(d) Ethanol in 25.0 g of ethanol (C2H5OH)

0.54 mol

(e) Silver chloride in 125 g of silver chloride (AgCl)

0.87 mol

(f) Aluminium nitrate in 4.5 g of aluminium nitrate (Al(NO3)2)

0.03 mol

2. Calculate the mass of (by using m = n x M)

(a) 1.25 mole of sodium hydroxide (NaOH)

50 g

(b) 0.25 mole of zinc metal (Zn)

16.35 g

(c) 20.0 mol of lead nitrate (Pb(NO3)2)

6624 g

(d) 3.5 mol of octane (C8H18)

399 g
 The Mole Part 2
(e) 0.025 mol of copper II sulfate (CuSO4)

3.9 g
(f) 0.025 mol of silver nitrate (AgNO3)

4.25 g

MOLES/MASS CONSTITUENTS

The formula of any given substance indicates the number of atoms (or ions) present in a molecule
(or formula unit) of that substance.

1 molecule of H2SO4 contains – 2 atoms of hydrogen, 1 atom of sulfur and 4 atoms of oxygen. We
can use the same logic when considering moles of a substance. 1 mole of H 2SO4 contains – 2
moles of hydrogen, 1 mole of sulfur and 4 moles of oxygen.

5 moles of Al2(SO4)3 contains – 10 moles of Al 3+ ions (5 x 2), 15 moles of SO4 3 – ions (5 x 3), 15
moles of sulfur atoms (5 x 3) and 60 moles of oxygen atoms (5 x 12).

QUESTIONS

3. Complete the following – 10 molecules of phosphoric acid (H3PO4) contains:

(a) How many atoms of hydrogen: 30

(b) How many atoms of phosphorous: 10

(c) How many atoms of oxygen: 40

4. Complete the following – 2.0 moles of ethanol molecules (CH3CH2OH) contains:

(a) How many mol of C atoms: 2

(b) How many mol of H atoms: 6

(c) How many mol of O atoms: 1

5. A sample of Mg(NO3)2 has a mass of 296.6 g. Determine for this sample the number of:

(a) Moles of Mg(NO3)2

2 mol

(b) Moles of NO3 – ions

4 mol

(c) Mass of Mg atoms

CALCULATIONS – NUMBER PARTICLES/MOLES/MASS

The following overview of mole relationships is useful for dealing with calculations such as those
shown in the example below.

EXAMPLES

1. A balloon is filled with 10.0 g of hydrogen gas (H 2). Calculate (a) the moles of hydrogen
molecules and (b) the number of hydrogen molecules in this amount of hydrogen gas.

m 10
(a) n (H2) = = = 5 mol of H2 gas
M 2

(b) N (H2) = n x 6.02 x 10 23 = 5 x 6.02 x 10 23 = 3.01 x 10 24 molecules of hydrogen

2. How many lead atoms are there in 10.0 grams of lead?

m 10
n (Pb) = = = 0.0483 mol
M 207.2

N (Pb) = n x 6.02 x 10 23 = 0.0483 x 6.02 x 10 23 = 2.91 x 10 22 atoms of lead

21
3. A drop of water contains 3.30 x 10 molecules of water. Calculate the mass of this drop of
water.

N 3.30× 1021
n (H2O) = = = 0.00548 mol
6.02× 1023 6.02× 1023

m (H2O) = n x M = 0.00548 x 18.0 = 0.098 g of water

QUESTIONS

6. What is the mass of Avogadro’s Number of atoms of calcium?

40.1 g

7. What is the mass of 12.04 x 10 23 molecules of hydrogen chloride (HCl)?

73 g

8. How many atoms of iron are contained in 0.1 mol of iron?

6.02 x 1022

9. How many atoms of iron are contained in 3 moles of iron III oxide (Fe2O3)?

3.612 x 1024

10. Determine the number of moles of sulfur and oxygen atoms in 0.2 mole of sulfur dioxide (SO2).

0.2 mol - sulfur

11. Find the number of moles of hydroxide ions in 0.25 mole of magnesium hydroxide (Mg(OH)2).

0.5 mol

12. What is the molar mass of 1 mole of nitrogen molecules (N2) and 1 mole of nitrogen atoms?

28 g – N2
14 g - N

13. Determine the mass of 1 mole of copper II sulfate pentahydrate (CuSO4.5H2O).

249.7 g

14. What is the mass of 0.2 mole of silver oxide (Ag2O)?

46.4 g

15. What is the mass of 5 moles of sodium sulfide (Na2S)?

390.5 g

16. Calculate the number of moles of lead II chloride (PbCl2) in 83.4 g of lead II chloride.

0.3 mol

17. Find the number of moles of potassium in (a) 0.1 mole of potassium hydrogensulfate (KHSO 4)
and (b) 87 g of potassium sulfate (K2SO4).

(a)

0.1 mol

(b)

0.5 mol
 The Mole Part 2
18. How many grams of carbon are contained in 2.5 moles of calcium hydrogen carbonate
(Ca(HCO3)2)?

60 g
19. Determine (a) the number of moles of nitrogen dioxide (NO 2) in 9.2 g of nitrogen dioxide and
(b) the mass of nitrogen in 9.2 g of nitrogen dioxide.

(a)

0.2 mol

(b)

2.8 g

20. If 1.2 moles of an organic compound has a mass of 84 g, what is the molar mass of this
compound?

70 g

21. Calculate the mass of 1.5 moles of silver nitrate (AgNO3).

255 g

22. What is the number of moles of sodium in 284 g of sodium carbonate (Na2CO3)?

5.4 mol

23. Find the mass of chlorine in 0.2 mole of sodium chloride (NaCl).

7.1 g

24. Determine the number of moles of calcium in 29.6 g of calcium hydroxide (Ca(OH)2).

0.4 mol

THE MOLE PART 2 ANSWERS

1. (a) 2 moles (b) 0.2 mole (c) 0.274 mole (d) 0.543 mole (e) 0.87 mole (f) 0.03 mole
2. (a) 50 g (b) 16.35 g (c) 6.6 kg (d) 399 g (e) 3.99 g (f) 4.25 g
3. (a) 30 atoms (b) 10 atoms (c) 40 atoms
4. (a) 4 mole (b) 12 mole (c) 2 mole
5. (a) 2 mole (b) 4 mole (c) 48.6 g
6. 40.1 g
7. 73 g
8. 6.02 x 1022 atoms
9. 3.612 x 1024 atoms
10. n (S) = 0.2 mole, n (O) = 0.4 mole
11. n (OH –) = 0.5 mole
 The Mole Part 2
12. M (N2) = 28 g M (N) = 14 g
13. 249.6 g
14. 46.4 g
15. 390.5 g
16. 0.299 mole
17. (a) 0.1 mole (b) 0.5 mole
18. 60 g
19. (a) 0.2 mole (b) 2.8 g
20. 70 g
21. 255 g
22. n (Na) = 5.36 mole
23. m (Cl) = 7.1 g
24. n (Ca) = 0.4 mole