GCSE Chemistry - Relative Formula Mass #24

The video tutorial explains how to find the mass number of elements and the relative atomic mass, denoted as AR. It covers calculating the relative formula mass (Mr) of compounds by adding the relative atomic masses of all atoms in a compound's molecular formula. Examples include magnesium chloride and sulfuric acid. The tutorial also demonstrates how to calculate the percentage mass of an element in a compound, using sulfuric acid and calcium hydroxide as examples.

What does the mass number of an element represent?

• The number of protons in the nucleus

• The number of neutrons in the nucleus

• The number of protons plus neutrons in the nucleus

• The average mass of all isotopes of the element

How is the relative atomic mass (AR) of an element determined?

• By counting the number of protons

• By averaging the mass of all isotopes

• By measuring the atomic radius

• By adding the number of protons and neutrons

What is the relative formula mass (Mr) of magnesium chloride (MgCl2)?

• 120

• 59

• 95

• 71

How do you calculate the percentage mass of an element in a compound?

• Divide the AR of the element by the total number of atoms

• Multiply the AR of the element by the number of atoms, divide by Mr, and multiply by 100

• Add the AR of the element to the Mr and multiply by 100

• Subtract the AR of the element from the Mr and multiply by 100

What is the percentage mass of oxygen in calcium hydroxide (Ca(OH)2)?

• 25.0%

• 50.0%

• 43.2%

• 32.4%