(U2) Formulae And Amounts Of A Substance

Question 1

What is empirical formula?

Answer 1

A formula which shows the simplest whole number ratio of atoms of each element in a compound

Question 2

What is molecular formula?

Answer 2

A formula which shows the actual number of atoms of each element in a molecule

Question 3

What is meant by molar gas volume?

Give an example

Answer 3

• The volume of one mole of gas under specified conditions of temperature and pressure
• e.g. 24 dm³ at 20°C (293K) and 1 atm pressure

Question 4

State the equation for Avogadro’s Law on gases at 20ºC and 1 atm pressure

Answer 4

Volume = number of moles x 24

V = N x 24

dm³ = mol x 24

V
N | 24

Question 5

What is the equation for percentage yield?

Answer 5

Actual yield / theoretical yield x 100

Question 6

What is the equation for atom economy?

Answer 6

Mr of desired product / total Mr of products x 100

Question 7

What is the formula used to determine a hydrocarbon?

Answer 7

C_xH_y + (X + y/4)O₂ —> XCO₂ + (y/2)H₂O

Question 8

What is the word equation for determining the volume of oxygen in hydrocarbon combustion reactions?

Answer 8

Volume of oxygen = (initial contraction - volume of C_xH_y) + volume of CO₂