Further calculations [Higher tier only] test questions - WJEC

1

What is the equation showing the number of moles present in a substance?

Number of moles = mass × M_r

Number of moles = M_r ÷ mass

Number of moles = mass ÷ M_r

2

What is the mass of 4 mol of carbon dioxide molecules?

M_r of carbon dioxide, CO₂ = 44

176 g

44 g

11 g

3

What is the empirical formula for hydrogen peroxide which has a molecular formula of H₂O₂?

H₂O₂

H₂O

4

The empirical formula for a compound is CH₂ and its relative formula mass (M_r) is 70. What is its molecular formula? Use the periodic table to help you.

CH₂

C₅H₁₀

C₇₀H₁₄₀

5

What is the mass of 5 moles of carbon?

A_r of carbon, C = 12

2.4 g

0.42 g

60 g

6

How many moles of water (H₂O) are in 90 g of water?

A_r of hydrogen, H = 1

A_r of oxygen, O = 16

0.2

7

What mass of carbon monoxide is required to produce 11.2 tonnes of iron from iron(III) oxide?

Fe₂O₃ + 3CO → 2Fe + 3CO₂

5.6 tonnes

8.4 tonnes

2.8 tonnes

8

Group 1 metals, such as sodium, are extremely reactive. When sodium (Na) is reacted with water (H₂O), sodium hydroxide (NaOH) and hydrogen (H₂) are formed. If 6.9 g of Na are reacted with water, 12.0 g of NaOH should be produced. In the actual experiment, only 6.4 g of NaOH were produced. What is the percentage yield?

187.5%

57.5%

53.3%

9

A chloride of iron, with a mass of 12.7 g, contained 5.6 g of iron. What is the empirical (simplest) formula of the iron chloride?

A_r of iron, Fe = 56

A_r of chlorine, Cl = 35.5

Fe₂Cl

FeCl₂

FeCl₄

10

A hydrocarbon was found to contain 72 g of carbon and 16 g of hydrogen. Using the figures given below, calculate the simplest formula for this hydrocarbon.

A_r of carbon, C = 12

A_r of hydrogen, H = 1

C₆H₁₆

C₁H₃

C₃H₈