Grade 9 · Science · Unit 5 of 12
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.
Saskatchewan Curriculum outcome: AE9.1, AE9.3 · physical and chemical properties, elements and compounds
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
What is the chemical formula for water?
- OH
- HO₂
- H₂O₂
- H₂O
Show answer
H₂O
Hint: Two hydrogen atoms and one oxygen atom.
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.
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.
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.
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.
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.