Calculating Masses Using Equations Flashcards

1️⃣ Familiarise yourself with the flashcards:

  • Look through all the flashcards to see what's on both sides.
  • Make sure you understand the information on each card. If something's unclear, click the link to the revision notes at the bottom of the page for more details.

2️⃣ Test yourself:

  • Look at the question or prompt on each card and try to remember the answer before flipping it over.
  • Check the answer and make a note of any cards you find challenging and need to go over more.

3️⃣ Consistently Review and Practice:

  • Use spaced repetition: spend more time on the cards you struggle with and go over them more often.
  • Regularly review all the flashcards to help you better understand and retain the information over time.

Note: We may include questions that have multiple correct answers. It's useful to remember specific examples to understand these concepts better.

PERSONALISED 1-TO-1 TUTORING

Need more help on this topic? Get 1-to-1 support

Get support with clear explanations, practice and feedback (Ages 5 to 16).

  • DBS-checked tutors
  • Flexible times
  • Parents can be updated
Book a free 10-min call See pricing

Want an ad-free experience? Subscribe to remove ads

In chemistry, what do we mean by 'calculating masses using equations'?

Using a balanced symbol equation to work out the mass of reactants or products from a known mass.

Why must a symbol equation be balanced before you use it to calculate masses?

Because the balancing numbers show the mole ratio of each substance, which you need to link their amounts.

How do you find the relative formula mass (Mr) of a compound?

Add together the relative atomic masses (Ar) of all the atoms in its formula.

What formula links mass, Mr and moles in reacting mass calculations?

Number of moles = mass (g) ÷ Mr.

How do you calculate the mass of a substance when you know its number of moles and Mr?

Mass (g) = number of moles × Mr.

List the three main steps to find the mass of a product from the mass of a reactant.

1) Use the mass and Mr to find moles of the known substance. 2) Use the balanced equation to find moles of the unknown substance. 3) Use its Mr to change those moles back to a mass.

How do you use the big numbers in a balanced equation in a mass calculation?

They give the ratio of moles that react and form, so you scale the moles of one substance to find the moles of another.

In the reaction 2H₂ + O₂ → 2H₂O, what mass of water is made from 2.0 g of hydrogen gas?

Mr of H₂ = 2, so moles of H₂ = 2.0 ÷ 2 = 1.0 mol. The ratio 2H₂ : 2H₂O means 1.0 mol H₂ makes 1.0 mol H₂O. Mr of H₂O = 18, so mass of water = 1.0 × 18 = 18 g.

Calcium carbonate, CaCO₃, breaks down to make carbon dioxide, CO₂. If 0.50 mol of CO₂ forms, what mass of CO₂ is this?

Mr of CO₂ = 12 + 16 + 16 = 44. Mass = moles × Mr = 0.50 × 44 = 22 g.

How can conservation of mass help you to check a reacting mass calculation?

The total mass of reactants should equal the total mass of products, so your answers should not create or lose mass overall.

Previous Topic
Back to Lesson
Next Topic