Topic 3: Quantitative Chemistry (AQA GCSE Chemistry)
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What is the relative atomic mass (Ar)?
The average mass of an atom of an element compared to 1/12th of the mass of carbon-12
What is the relative molecular mass (Mr)?
The sum of the relative atomic masses of all atoms in a molecule
How do you calculate the relative formula mass?
Add up the relative atomic masses of all atoms in an ionic compound’s formula
What is the mole?
The amount of substance containing Avogadro’s number (6.02 × 10²³) of particles
What is Avogadro’s number?
A: 6.02 × 10²³ particles per mole
Q: How do you calculate the number of moles?
A: Moles = mass ÷ relative formula mass (Mr)
Q: What is the formula to calculate concentration?
A: Concentration = amount of solute (mol) ÷ volume of solution (dm³)
Q: How many cm³ are in 1 dm³?
A: 1000 cm³
Q: What is the law of conservation of mass?
A: Mass is conserved in chemical reactions; it is neither created nor destroyed
Q: How do you calculate percentage yield?
A: (Actual yield ÷ theoretical yield) × 100
Q: What is the theoretical yield?
A: The maximum amount of product predicted by the balanced chemical equation
Q: What is atom economy?
A: A measure of how much of the reactants end up as useful products
Q: How do you calculate atom economy?
A: (Mr of desired product ÷ sum of Mr of all products) × 100
Q: Why is high atom economy important?
A: It means less waste and more sustainable chemical processes
Q: What is a limiting reactant?
A: The reactant that runs out first and limits the amount of product made
Q: What is an excess reactant?
A: A reactant that is not used up completely in a reaction
Q: How do you use a balanced chemical equation in calculations?
A: Use the mole ratio from the equation to relate amounts of reactants and products
Q: What is the formula for calculating mass from moles?
A: Mass = moles × Mr