AQA GCSE Combined Science Chemistry - Quantitative chemistry (paper 1)
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23 Terms
What is relative formula mass (Mr)?
The sum of the relative atomic masses (Ar) of all atoms in a compound.
How do you calculate Mr of a compound?
Add together the Ar values of each atom in the formula.
What is the Ar of oxygen?
16
What is the Mr of CO₂?
12 + (2 × 16) = 44
What is the law of conservation of mass?
mass is the same as the product and reactant’s mass
Why might mass increase in a reaction?
A gas (e.g. oxygen) is added from the air.
Why might mass decrease in a reaction?
A gas is produced and escapes into the air.
What is a mole?
The amount of a substance containing 6.02 × 10²³ particles (Avogadro’s number).
What is the formula to calculate moles?
Moles = Mass (g) ÷ Mr
What is the formula to calculate mass?
Mass = Moles × Mr
What is the formula to calculate Mr?
Mr = Mass ÷ Moles
What is the limiting reactant?
The reactant that is completely used up first in a reaction.
What is meant by excess reactant?
A reactant that is not completely used up – some is left over.
Why is it important to use a limiting reactant?
To make sure the reaction stops at a predictable point and waste is minimised.
What is concentration?
The amount of solute dissolved in a given volume of solution.
What is the formula for concentration (in g/dm³)?
Concentration = Mass of solute (g) ÷ Volume of solution (dm³)
How do you convert cm³ to dm³?
Divide by 1000
How do you increase the accuracy of a concentration calculation?
Use precise equipment (e.g. pipettes, burettes), and repeat to find a mean.
What is the unit for concentration ?
g/dm³
acid + alkali
= salt + water
when an acid reacts with and alkali a salt and water are produced under what condition
it has fully reacted
acids have a pH of
1-6
alkali’s have a pH of
8-14