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Grade 9 · Science · Unit 7 of 11

Elements & Compounds

Formulas, properties and changes

What your child practises

Elements, compounds and mixtures, reading chemical formulas, physical and chemical properties and changes, density, and common household chemicals, including why some should never be mixed.

Ontario Curriculum expectation: C2.1, C2.6, C2.7 · physical and chemical properties of elements and compounds, density, chemical formulas and household products

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    What is the chemical formula for water?

    • OH
    • HO₂
    • H₂O₂
    • H₂O
    Show answer

    H₂O

    Hint: Two hydrogen atoms and one oxygen atom.

  2. Question 2

    Aluminum foil is easy to shape into a sheet without breaking. This property is called…

    • malleability
    • flammability
    • solubility
    • brittleness
    Show answer

    malleability

    Hint: Malleable materials can be hammered or rolled into thin sheets.

  3. Question 3

    How many atoms are in one unit of ethane, C₂H₆?

    answer box

    Show answer

    8

    Hint: Add the subscripts, counting a missing subscript as 1, in C₂H₆. The total is 8.

  4. Question 4

    In the formula CO₂, what does the small 2 mean?

    • There are two molecules
    • There are two carbon atoms
    • The charge is 2
    • There are two oxygen atoms in each molecule
    Show answer

    There are two oxygen atoms in each molecule

    Hint: A subscript tells how many atoms of the element before it.

  5. Question 5

    Element or compound? Sort each formula.

    Sort into: ⚛️ Element · 🧪 Compound

    • 💨O₂ (oxygen gas)
    • 🔩Fe (iron)
    • 🥇Au (gold)
    • 🧂NaCl (table salt)
    • 🌫️CO₂ (carbon dioxide)
    • 🔥CH₄ (methane)
    Show answer

    ⚛️ Element: O₂ (oxygen gas), Fe (iron), Au (gold) · 🧪 Compound: NaCl (table salt), CO₂ (carbon dioxide), CH₄ (methane)

    Hint: An element has one kind of atom in its formula. A compound has two or more different elements.

  6. Question 6

    A sample has a mass of 31.2 g and a volume of 4 cm³. What is its density in g/cm³?

    answer boxg/cm³

    Show answer

    7.8 g/cm³

    Hint: Density = mass ÷ volume = 31.2 ÷ 4 = 7.8 g/cm³.

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