GCSE Chemistry: Quantitative 1

What is relative formula mass (Mr)

The. sum of the relative atomic masses of all the atoms shown in the formula.

What is a mole?

Measurement of the amount of a substance

What is Avogadro constant?

6.02x10²³

What is the formula for mass?

mass (g) = Mr * moles

What is the conservation of mass?

In a reaction the total mass of the reactants must equal the total mass of the products.

Why does the combustion of metals appear to break the law of conservation of mass?

The product of metal oxide has a greater mass as the metal has reacted with oxygen in the air.

What is a thermal decomposition reaction?

Breaking down a substance using heat.

Why does thermal decomposition appear to not abide by conservation of mass?

One or more products is a gas and it may escape into the air so its mass cannot be measured.

Explain how to deduce balancing numbers in an equation from reacting masses

1. Calculate the moles of each substance

2. Find the simplest whole number ratio by dividing all the mole values by the smallest mole value

3. If this does not give a whole number ratio multiply up by factors of 2,3,4 etc

What is an excess?

When the amount of reactant is greater than the amount that can react.

What is a limiting reactant?

the reactant that determines the amount of product that can be formed by a reaction

What is yield?

The amount of product formed in a reaction.

What is percentage yield?

The amount of product formed in a reaction compared to the maximum theoretical mass that could be produced as a percentage.

What is atom economy (atom utilisation)?

Atom economy is a measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation.

What is the formula for atom economy?

100 * (sum of Mr of desired product / sum of Mr of all reactants)