BECE Matter, Elements, and Compounds 3 — Questions and Answers
Question 1: How can a mixture be distinguished from a compound?
- Mixtures always have a fixed composition
- Compounds can be separated by physical means
- Mixtures can be separated by physical means (Correct answer)
- Compounds have variable composition
Correct answer: Mixtures can be separated by physical means
Mixtures can be separated by physical methods like filtration or magnetism, while compounds require chemical reactions to separate.
Question 2: Which of the following is a heterogeneous mixture?
- Salt water
- Air
- Vinegar
- Soil (Correct answer)
Correct answer: Soil
Soil is heterogeneous because its composition is not uniform — different particles of sand, clay, and organic matter are visible.
Question 3: What method would best separate a mixture of iron filings and sand?
- Filtration
- Distillation
- Using a magnet (Correct answer)
- Evaporation
Correct answer: Using a magnet
A magnet attracts iron filings but not sand, making magnetic separation the most effective method.
Question 4: Air is classified as a mixture rather than a compound because:
- It contains only nitrogen and oxygen
- Its components can be separated and their proportions vary (Correct answer)
- It has a definite chemical formula
- It is always found in the gaseous state
Correct answer: Its components can be separated and their proportions vary
Air has variable composition (proportions of N₂, O₂, CO₂, etc. vary) and its components can be physically separated.
Question 5: Which separation technique works best for recovering dissolved salt from salt water?
- Filtration
- Using a magnet
- Chromatography
- Evaporation (Correct answer)
Correct answer: Evaporation
Evaporating the water leaves behind the dissolved salt as solid crystals.
Question 6: When iron and sulfur are heated together and form iron sulfide, what evidence shows a compound — not a mixture — was formed?
- The mixture looks gray
- Both substances can still be separated by a magnet
- The new substance has different properties from either iron or sulfur (Correct answer)
- The temperature stays the same
Correct answer: The new substance has different properties from either iron or sulfur
Iron sulfide cannot be separated by a magnet and has different properties from iron and sulfur, confirming it is a compound.
Question 7: Which of the following best describes a homogeneous mixture?
- A mixture where different parts are visible to the naked eye
- A mixture with uniform composition throughout (Correct answer)
- A mixture that cannot be separated by any method
- A mixture composed only of compounds
Correct answer: A mixture with uniform composition throughout
A homogeneous mixture has the same composition and properties throughout, such as salt water or air.
BECE Matter, Elements, and Compounds 3
How can a mixture be distinguished from a compound?