Question

(A) How many moles (of molecules or formula units) are in each sample? And please explain how the answer is found.

1) 20.0 g NO2

2) 1.35 kg CO2

3) 40.4 g KNO3

4) 102.3 kg Na2SO4

(B) How many molecules (or formula units) are in each sample? And please show how to find answer

1) 52.03 g CCl4
2) 73.85 kg NaHCO3

3) 123.22 g C4H10

4) 3.15×10⁴ g Na3PO4

Answer 1

A)

1)

Molar mass of NO2,

MM = 1*MM(N) + 2*MM(O)

= 1*14.01 + 2*16.0

= 46.01 g/mol

mass(NO2)= 20.0 g

use:

number of mol of NO2,

n = mass of NO2/molar mass of NO2

=(20.0 g)/(46.01 g/mol)

= 0.4347 mol

Answer: 0.435 mol

2)

Molar mass of CO2,

MM = 1*MM(C) + 2*MM(O)

= 1*12.01 + 2*16.0

= 44.01 g/mol

mass(CO2)= 1.35 Kg

= 1350.0 g

use:

number of mol of CO2,

n = mass of CO2/molar mass of CO2

=(1350.0 g)/(44.01 g/mol)

= 30.67 mol

Answer: 30.7 mol

3)

Molar mass of KNO3,

MM = 1*MM(K) + 1*MM(N) + 3*MM(O)

= 1*39.1 + 1*14.01 + 3*16.0

= 101.11 g/mol

mass(KNO3)= 40.4 g

use:

number of mol of KNO3,

n = mass of KNO3/molar mass of KNO3

=(40.4 g)/(1.011*10^2 g/mol)

= 0.3996 mol

Answer: 0.400 mol

4)

Molar mass of Na2SO4,

MM = 2*MM(Na) + 1*MM(S) + 4*MM(O)

= 2*22.99 + 1*32.07 + 4*16.0

= 142.05 g/mol

mass(Na2SO4)= 102.3 Kg

= 102300.0 g

use:

number of mol of Na2SO4,

n = mass of Na2SO4/molar mass of Na2SO4

=(102300.0 g)/(1.421*10^2 g/mol)

= 7.202*10^2 mol

Answer: 7.20*10^2 mol

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