What mistakes do students make with Atom economy?

Multiplying concentration by volume in cm³ without converting. Put it right by dividing the volume by 1000 first. Using relative formula mass as if it were the mass in grams without multiplying by moles. Put it right by applying mass = moles × molar mass. Adding relative atomic masses incorrectly when finding molar mass. Put it right by using the formula and checking each element's subscript.

What are the exam tips for Atom economy in Chemistry AQA GCSE?

Write down the values you know with units, then choose the equation that links them. Convert cm³ to dm³ in a separate step so you do not lose track of the factor of 1000. Check that your final mass is sensible: a small volume of dilute solution should give a small mass.

AQA · GCSE · Chemistry

Course version: 8462 · Version from Sept 2018

The amount in moles of solute or the mass in grams of solute in a given…

Full specification wording

Atom economy: The amount in moles of solute or the mass in grams of solute in a given volume of solution can be calculated from its concentration in mol/dm .

Note: This content officially belongs to section 4.3.4 Using concentrations of solutions in mol/dm³ and is strictly Higher Tier only.

Checked against the AQA 8462 specification (opens in a new tab) on 21 September 2026.

Point 5 of 7

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

Calculate moles of solute using amount = concentration × volume in dm³.
Convert a volume in cm³ to dm³ by dividing by 1000 before multiplying by concentration.
Calculate molar mass from the chemical formula using relative atomic masses.
Calculate mass of solute using mass = moles × molar mass, with correct units.
Show a clear sequence: volume conversion, moles, then mass, so each step can be followed.

Common mistakes and how to put them right

Multiplying concentration by volume in cm³ without converting.
Put it right by dividing the volume by 1000 first.
Using relative formula mass as if it were the mass in grams without multiplying by moles.
Put it right by applying mass = moles × molar mass.
Adding relative atomic masses incorrectly when finding molar mass.
Put it right by using the formula and checking each element's subscript.

Exam tips

Write down the values you know with units, then choose the equation that links them.
Convert cm³ to dm³ in a separate step so you do not lose track of the factor of 1000.
Check that your final mass is sensible: a small volume of dilute solution should give a small mass.

Try the lesson

The start of the Atom economy: The amount in moles of solute or the mass in grams of solute in a given volume of solution can be calculated from its concentration in mol/dm . lesson, made from checked teaching notes for this specification point.

Have a go first

Which equation correctly calculates the amount in moles of solute in a solution from its concentration in mol/dm³?

Tip: press 1 to 4 to choose

Listen

Note: This content officially belongs to section 4.3.4 Using concentrations of solutions in mol/dm³ and is strictly Higher Tier only. If you know a solution's concentration and volume, you can find the amount of solute in moles using amount = concentration × volume in dm³. From moles, you can find mass using mass = moles × molar mass. For example, 250 cm³ of 0.200 mol/dm³ NaOH contains 0.200 × 0.250 = 0.0500 mol. NaOH has molar mass 40.0 g/mol, so the mass is 0.0500 × 40.0 = 2.00 g. Always convert volume to dm³ first. The molar mass must be calculated from the formula using relative atomic masses. This skill links to the mole concept and is essential for titration calculations. A strong answer earns marks for these points. Calculate moles of solute using amount = concentration × volume in dm³. Convert a volume in cm³ to dm³ by dividing by 1000 before multiplying by concentration. Calculate molar mass from the chemical formula using relative atomic masses. Calculate mass of solute using mass = moles × molar mass, with correct units. A common slip: Multiplying concentration by volume in cm³ without converting. Instead, dividing the volume by 1000 first. Exam tip: Write down the values you know with units, then choose the equation that links them.

See it

A flowchart running top to bottom. A box labelled 'Volume of solution in cm³' leads to a box labelled 'Convert volume to dm³ (divide by 1000)', which leads to a box labelled 'Amount in moles = concentration × volume in dm³'. Separately, a box labelled 'Chemical formula' leads to a box labelled 'Molar mass from relative atomic masses'. Both the moles box and the molar mass box lead into a box labelled 'Mass in grams = moles × molar mass', which leads to a final box labelled 'Mass of solute in grams'. — It shows the sequence from volume in cm³ through conversion to dm³ and calculation of moles, combined with molar mass, to give the mass of solute.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A flowchart running top to bottom. A box labelled 'Volume of solution in cm³' leads to a box labelled 'Convert volume to dm³ (divide by 1000)', which leads to a box labelled 'Amount in moles = concentration × volume in dm³'. Separately, a box labelled 'Chemical formula' leads to a box labelled 'Molar mass from relative atomic masses'. Both the moles box and the molar mass box lead into a box labelled 'Mass in grams = moles × molar mass', which leads to a final box labelled 'Mass of solute in grams'.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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