Back to the lesson plan builder
Lesson length30 min45 min60 min
Questions🔀 New questions

Print the plan for yourself; the student sheet prints on its own page after it.

Science lesson plan · 11th grade (Year 12 in England) · 45 minutes

Percentage by mass of an element in a compound

Atoms, elements and the periodic table

CCSS NGSS.HS-PS1-7England: GCSE Combined Science: Quantitative chemistry

Objective and success criteria

Students will: Percentage by mass of an element in a compound.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Relative formula mass

Leads to: Find empirical and molecular formulae

Materials: Periodic tables, Atom model kits, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 5 min

  • Quick retrieval from earlier learning (Relative formula mass). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Calculate the relative formula mass (Mr) of CO₂. Relative atomic masses: C = 12, O = 16. → 44Prompt: Multiply each relative atomic mass by the number of those atoms.
  2. Calculate the relative formula mass (Mr) of iron(III) oxide, Fe₂O₃. Relative atomic masses: Fe = 56, O = 16. → 160Prompt: Count the atoms of each element first, including any brackets.
  3. What is the percentage by mass of oxygen in (NH₄)₂SO₄? Relative atomic masses: N = 14, H = 1, S = 32, O = 16. Give 1 decimal place. → 48.5 %Prompt: Work out Mr first.

Hook · 5 min

  • Show the periodic table and ask what patterns students can see before anything is explained.
  • Share the objective: Percentage by mass of an element in a compound. Read the success criteria together.

I do: model it · 10 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: What is the percentage by mass of carbon in carbon dioxide, CO₂? (Ar: C = 12, O = 16) Give 1 decimal place.
  • Step 1: Mr = 44
  • Step 2: 12 ÷ 44 × 100 = 27.27
  • Step 3: So the answer is: 27.3 %
  • Answer: 27.3 %
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 10 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. What is the percentage by mass of calcium in calcium carbonate, CaCO₃? (Ar: Ca = 40, C = 12, O = 16) Give 1 decimal place. → 40 %Prompt: Work out Mr of the compound first.
  2. What mass of magnesium is in 80 g of MgO? (Ar: Mg = 24, O = 16) → 48 gPrompt: Find what fraction of the compound's mass is the element.

You do: independent practice · 10 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. What mass of iron is in 800 g of Fe₂O₃? (Ar: Fe = 56, O = 16) → 560 gPrompt: Find what fraction of the compound's mass is the element.
  2. Fertiliser bags often show the percentage of nitrogen. Why is this useful to farmers? (They can work out how much nitrogen the crop actually receives / It tells them the fertiliser is organic / It shows how heavy the bag is / It shows the price) → They can work out how much nitrogen the crop actually receivesPrompt: Plants need nitrogen for proteins.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Relative formula mass.
  • Use concrete materials: periodic tables.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Move on to: Find empirical and molecular formulae.
  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.

Free lesson plan from eurekami.com/lesson-plan-builder

eurekami

Percentage by mass of an element in a compound

Name

Date

Score/ 8

  1. Question 1

    What mass of calcium is in 500 g of CaCO₃? (Ar: Ca = 40, C = 12, O = 16)

    Answerg

  2. Question 2

    What is the percentage by mass of calcium in calcium carbonate, CaCO₃? (Ar: Ca = 40, C = 12, O = 16) Give 1 decimal place.

    Answer%

  3. Question 3

    Fertiliser bags often show the percentage of nitrogen. Why is this useful to farmers?

    • A. They can work out how much nitrogen the crop actually receives
    • B. It shows how heavy the bag is
    • C. It shows the price
    • D. It tells them the fertiliser is organic

  4. Question 4

    What mass of carbon is in 360 g of C₆H₁₂O₆? (Ar: C = 12, H = 1, O = 16)

    Answerg

  5. Question 5

    What mass of iron is in 800 g of Fe₂O₃? (Ar: Fe = 56, O = 16)

    Answerg

  6. Question 6

    What is the percentage by mass of carbon in glucose, C₆H₁₂O₆? (Ar: C = 12, H = 1, O = 16) Give 1 decimal place.

    Answer%

  7. Question 7

    What mass of nitrogen is in 400 g of NH₄NO₃? (Ar: N = 14, H = 1, O = 16)

    Answerg

  8. Question 8

    What is the percentage by mass of sulfur in sulfuric acid, H₂SO₄? (Ar: H = 1, S = 32, O = 16) Give 1 decimal place.

    Answer%

Free from eurekami.com

for the adult only

Answer key: Percentage by mass of an element in a compound

  1. 1. 200 g

  2. 2. 40 %

  3. 3. A. They can work out how much nitrogen the crop actually receives

  4. 4. 144 g

  5. 5. 560 g

  6. 6. 40 %

  7. 7. 140 g

  8. 8. 32.7 %