Quantitative ChemistryWorked Example

Worked Example — Full Method

Part of Moles & Calculations · GCSE GCSE Chemistry revision

This worked example covers Worked Example — Full Method within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 27 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 9 of 17 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.

Topic position

Section 9 of 17

Practice

27 questions

Recall

20 flashcards

🧮 Worked Example — Full Method

Question: What mass of magnesium oxide forms when 4.8g of magnesium burns completely?
Equation: 2Mg + O₂ → 2MgO (Ar: Mg = 24, O = 16)

Step 1: Balanced equation
2Mg + O₂ → 2MgO ✓

Step 2: Identify known and unknown
Known: 4.8g of Mg
Unknown: mass of MgO

Step 3: Calculate moles of known (Mg)
n = m ÷ Mr
n = 4.8 ÷ 24
n = 0.2 mol of Mg

Step 4: Use the ratio
From equation: 2Mg : 2MgO = 1:1 ratio
So 0.2 mol Mg produces 0.2 mol MgO

Step 5: Convert to mass
Mr of MgO = 24 + 16 = 40
m = n × Mr
m = 0.2 × 40
m = 8.0g

Step 6: Check
Started with 4.8g Mg, added oxygen → got 8.0g product
Mass increased (oxygen added) ✓ Makes sense!

Answer: 8.0g of magnesium oxide

Keep building this topic

Read this section alongside the surrounding pages in Moles & Calculations. That gives you the full topic sequence instead of a single isolated revision point.

The 6-Step Calculation Method (Works Every Time!)Common Misconceptions The Story of Counting the Uncountable Moles Formula Triangle

Practice Questions for Moles & Calculations

One mole of any substance contains how many particles?

A. 6.02 × 10²³
B. 6.02 × 10²⁰
C. 3.01 × 10²³
D. 6.02 × 10¹⁸

1 markfoundation

Explain why the percentage yield of a reaction is never 100% in practice.

2 marksstandard

Quick Recall Flashcards

Define 'one mole'

The amount of substance containing 6.02 × 10²³ particles One mole of any element weighs exactly its Ar in grams

What is Avogadro's constant?

6.02 × 10²³ particles per mole This is the number of particles in one mole of any substance.

27 questions on Moles & Calculations — practise free

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The 6-Step Calculation Method (Works Every Time!)

Common Misconceptions