C3 - How Much?

Question 1

Work out the relative atomic mass of MgCl2

Answer 1

Mg mass number = 24
Cl (two atoms of chlorine) mass number = 35.5
24 + (35.5 x 2) = 95

Question 2

What is a mole?

Answer 2

A mole is a unit of the amount of a substance. One mole is equal to the relative atomic mass of an element in grams (g)

Question 3

What is the formula for number of moles?

Answer 3

Number of moles = Mass in g (of element or compound)
————————————
Mr = Relative atomic mass (of an element or compound)

Question 4

Work out the number of moles of 42g of Carbon

Answer 4

42g/12 = 3.5 moles

Question 5

What is the formula for calculating the percentage mass of an element?

Answer 5

relative atomic mass of whole compound x 100

Question 6

Fine the percentage mass of sodium in sodium carbonate Na2CO3

Answer 6

Relative atomic mass of sodium = 23
Two sodium atoms = 46
Relative atomic mass of carbon = 12
Relative atomic mass of oxygen = 16
Three oxygen atoms = 48
46+12+48 = 106

23x2
—– x 100 = 43.4%
106

Question 7

How do you calculate the mass of a product?

Answer 7

1. Write out a balanced equation
2. Work out the relative atomic mass of the reactant and product you WANT to know
3. Divide to get one then multiply to get all

Question 8

What mass of magnesium oxide is produced when 60g of magnesium is burned in the air?

2Mg + O2 —–> 2MgO

Answer 8

Relative atomic mass of two Mg atoms = 24 x 2 = 48
Relative atomic mass of two Mg + one O2 atom = 24 x 2 + 16 = 80
Mass of 2Mg = 48g/48 = 1g x 60 = 60g
Mass of 2MgO = 80g/48 = 1.67g x 60 = 100g
100g - 60 = 40g

Question 9

What is the formula for percentage yield?

Answer 9

Percentage yield = actual yield (grams)
                                  --------------------  x 100
                                  Predicted yield (grams

Question 10

Why are percentage yields never 100%?

Answer 10

1. Product can be lost during filtration
2. A reservable reaction could take place
3. Unexpected reactions can occur

Question 11

In the periodic table what is the top number of an element?

Answer 11

The relative atomic mass or mass number

Question 12

What is paper chromatography?

Answer 12

Artificial colours can be separated with it, the solvent seeps up the paper taking with it the dye and the dye forms spots in different places

Question 13

What is gas chromatography?

Answer 13

It is used to identify substances by separating them