Calculations Involving Masses - Paper 1

Question 1

Define relative formula mass

Answer 1

The relative formula mass (M_r) of a compound is the sum of the relative atomic mass (A_r) of every atom in it.

Question 2

Define empirical formula

Answer 2

The empirical formula of a compound is the simplest whole number ratio of atoms present in the compound.

Question 3

Describe an experiment to determine the empirical formula of magnesium oxide.

Answer 3

• Measure and record the mass of an empty crucible with its lid.
• Put a length of magnesium ribbon into the crucible.
• Measure and record the total mass of the crucible, its lid and contents.
• Place the crucible on a tripod with a pipe clay triangle. Strongly heat the crucible for several minutes using a Bunsen burner.
• When the magnesium has stopped glowing, turn off the Bunsen burner and allow the crucible to cool down.
• Measure and record the total mass of the crucible, its lid and contents.

Question 4

How many particles are in 1 mole of a substance?

Answer 4

6.02x10²³

Avogadro’s constant