Chapter 4 - The Mole

Question 1

What is one mole?

Answer 1

One mole of a substance is the amount of that substance that contains 6 by 10 to the power of 23, particles of that substance.

Question 2

Converting Moles to Grams

Answer 2

Mass of one mole of an element = Relative Atomic Mass in Grams.

Question 3

Converting Moles to grams in compounds

Answer 3

Mass of one mole of a compound = Relative Molecular Mass in grams.

Question 4

Converting Grams to Moles

Answer 4

To convert grams into moles we divide the number of grams by the RAM/RMM of that substance.

Question 5

Converting moles to gases

Answer 5

One mole = 22.4L of gas at standard temperature and pressure.
One mole = 24L at room temperature and pressure.

Question 6

How many grams are in one mole of Na2S2O3?

Answer 6

1 mole of Na2S2O3 =2(23)+2(32)+3(16)= 158g

Question 7

How many grams in one mole of Al2(SO4)3?

Answer 7

1 mole of Al2(SO4)3 = 2(27)+3(32+4(16))= 342g

Question 8

How many moles are in 379.5g of Na?

Answer 8

1 mole of sodium= 23g
x moles of sodium = 379.5g
x moles Na = 379.5/23= 16.5 moles

Question 9

How many litres is 5.6 moles of methane at s.t.p?

Answer 9

1 mole of CH4= 22.4L

5.6 moles of CH4 = 5.6 (22.4)= 125.44L

Question 10

How many moles is 9.4 litres of nitrogen at r.t.p?

Answer 10

1 mole of nitrogen = 24L

9.4/24 = 0.392 moles

Question 11

How many cm cubed is 6 moles of CO2 at r.t.p?

Answer 11

1 mole of CO2 = 24,000cm3
6 moles of CO2 = 6(24,000)
6 moles = 144,000cm3

Question 12

Calculate the % composition by mass of oxygen in H2O?

Answer 12

1 mole of O = 16 grams
1 mole of H2O = 2(1)+16= 18 grams
16/18 x 100/1 = 88.8%

Question 13

Calculate the % composition by mass of Oxygen in H2O?

Answer 13

1 mole of O =16g
1 mole of H2O= 2(1) + 16=18g
16/18 x 100/1 = 88.8%

Question 14

What is the law of conservation of mass?

Answer 14

The law of conservation of mass states that the total mass of the products of a chemical reaction is the same at the total mass of its reactants.

Question 15

What is the law of conservation of matter?

Answer 15

The law of conservation of matter states that in any chemical reaction, matter is neither created or destroyed but merely changes from one form to another.

Question 16

Balance the equation CH4 + O2 —- CO2 + H20

Answer 16

CH4 + 2O2 —- CO2 + 2H20
C: 1 C: 1
O: 2 (4) O: 3 (4)
H: 4 H: 2 (4)

Question 17

Mole Ratios — 2Mg + O2 —– 2MgO

4 MOLES

Answer 17

2Mg + O2 ——- 2MgO
2/2 : 1/2 : 2/2
1 : 1/2 : 1
4 MOLES : 2 MOLES : 4 MOLES

Question 18

Calculations based on balanced equations
- In a reaction, 14.7g of potassium dichromate reacted completely with concentrated hydrochloric acid according to the equation:
K2Cr2O7 + 14HCI – 2KCl + 2CrCl3 + 7H2O + 3Cl2
Ratio – 1 : 14 : 2 : 2 : 7 : 3
Our Ratio – 0.05 : 0.7 : 0.1 : 0.35 : 0.15
(i) How many moles of potassium dichromate were used?
- Rest of Questions in below flashcards

Answer 18

(i) Mass ——— Moles ( divide by RMM)
1 mole of K2Cr2O7 = 2(39) + 2(52) + 7(16) = 294g
– 14.7/294 = 0.05 Moles

Question 19

What is a molecular formula?

Answer 19

The molecular formula of a compound is a formula which shows the number and type of each atom present in a molecule.

Question 20

What is the empirical formula?

Answer 20

The empirical formula of a compound is the formula showing the simplest whole number ratio of the numbers of different atoms present in this molecule.

Question 21

(ii)How many moles of water were produced?

Answer 21

• 0.05 x 7 = 0.35 moles of water