🧪 GCSE Chemistry Revision Newsletter - Calculating Mass Changes

Part 1 - Keywords:

• Conservation of Mass

• Reactants

• Products

• Gas Escape

• Enclosed System

• Open System

• Metal Oxides

• Thermal Decomposition

• Particle Model

Part 2 - Key Facts:

• The law of conservation of mass states that no atoms are lost or made in a chemical reaction.

• Some reactions appear to show a mass change because a gas is involved but not accounted for.

• If a gas is produced and escapes, the measured mass decreases.

• If a gas reacts and joins, the measured mass increases.

• Examples:

  • Metal + Oxygen → Metal Oxide (Mass increases as oxygen from the air reacts).

  • Thermal decomposition of metal carbonates (Mass decreases as carbon dioxide gas escapes).

Part 3 - Quick Quiz:

1️⃣ What does the law of conservation of mass state?
2️⃣ Why might a reaction appear to lose mass?
3️⃣ Why does rusting make iron heavier?
4️⃣ Give an example of a reaction where the mass decreases.
5️⃣ What is an open system in a chemical reaction?

Answers:

1️⃣ The total mass before and after a reaction remains the same.
2️⃣ A gas product may escape, so it is not included in the measured mass.
3️⃣ Oxygen from the air reacts with iron, adding extra mass.
4️⃣ Thermal decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) loses mass because CO₂ escapes.
5️⃣ A reaction vessel where gases can escape into the surroundings.

Multiple Choice Questions:

1️⃣ What happens to the mass when magnesium burns in air?
a) It decreases because gas is released.
b) It stays the same because no atoms are lost.
c) It increases because oxygen from the air is added.
d) It decreases because magnesium evaporates.

2️⃣ Why does the mass decrease in the thermal decomposition of calcium carbonate?
a) The metal carbonate turns into a gas.
b) Carbon dioxide is produced and escapes.
c) The reaction absorbs oxygen.
d) The solid product weighs less than the reactant.

3️⃣ In a closed system, how does the total mass change during a reaction?
a) It increases as atoms are created.
b) It decreases because gases escape.
c) It remains the same as no atoms can enter or leave.
d) It decreases as solids dissolve.

Multiple Choice Answers:

1️⃣ c) It increases because oxygen from the air is added.
2️⃣ b) Carbon dioxide is produced and escapes.
3️⃣ c) It remains the same as no atoms can enter or leave.

Part 4 - Going Further:

Question:
A student burns magnesium in the air and finds that the product (magnesium oxide) has a higher mass than the original magnesium. Explain why.

Answer:
Magnesium reacts with oxygen from the air, which is added to the mass of the product. The extra mass comes from the oxygen atoms that bonded with magnesium.

Part 5 - Revision Tip:

To decide if a reaction gains or loses mass, ask:
✔️ Is a gas involved?
✔️ Is it entering (mass increases) or leaving (mass decreases)?
✔️ Is the system open (gas escapes) or closed (gas trapped)?

💡 Remember:
"Gas escapes, mass drops. Gas joins, mass pops!"

Part 6 - More Help:

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Part 7 - More Help:

Webpages

1. Mass Changes when a Reactant or Product is a Gas
   Save My Exams
   This page explains how chemical reactions involving gases can lead to apparent changes in mass, detailing scenarios where mass is gained or lost due to gaseous reactants or products.
2. Mass changes in chemical reactions | Experiment
   RSC Education
   This resource provides a practical experiment to observe mass changes during reactions involving gases, helping students understand the conservation of mass in open and closed systems.

YouTube Video

• Mass Changes when a Reactant or Product is a Gas
  YouTube
  This video offers a visual explanation of why mass changes occur in reactions involving gaseous reactants or products, aligning with the AQA GCSE Chemistry curriculum.

Stay tuned for the next issue, where we'll explore another key science concept! 🔬✨