Questions on Pure Substance
A pure substance is a form of matter that has a fixed composition and consistent properties throughout. Pure substances can be classified as elements, which consist of only one type of atom, or compounds, which are made of two or more elements chemically combined in definite proportions. Unlike mixtures, pure substances cannot be separated by physical means. Understanding pure substances is essential for studying matter, chemical reactions, and the organization of materials in chemistry.
As a Science Teacher and Education Specialist, I have developed these Pure Substance Questions to help students understand one of the fundamental concepts of chemistry and the classification of matter. Combining academic expertise with practical classroom experience, this resource strengthens scientific literacy and enables learners to distinguish pure substances from mixtures while recognizing the characteristics of elements and compounds. These exercises are designed for middle school, high school, and introductory college chemistry courses.
Multiple Choice Questions – Pure Substance
1. What is a pure substance?
A) A substance made of more than one element
B) A material that contains multiple phases
C) Matter with uniform and unchanging composition
D) A compound that can be separated physically
E) Any mixture with a single color
2. Which of the following is a pure substance?
A) Saltwater
B) Air
C) Vinegar
D) Distilled water
E) Milk
3. A compound is:
A) A heterogeneous mixture
B) A single element
C) A substance formed by chemical combination of two or more elements
D) A physical blend of elements
E) Always made of metals
4. Which of the following is an example of an element, a type of pure substance?
A) Water
B) Salt
C) Iron
D) Carbon dioxide
E) Ammonia
5. Pure substances can be classified as:
A) Elements and mixtures
B) Mixtures and solutions
C) Compounds and elements
D) Homogeneous and heterogeneous
E) Acids and bases
6. Which of the following is not a pure substance?
A) Oxygen gas
B) Tap water
C) Gold
D) Hydrogen gas
E) Carbon
7. What best describes the composition of a pure substance?
A) It varies depending on where it’s found
B) It is made up of more than one phase
C) It has a fixed and definite composition
D) It can be easily separated
E) It can only be liquid
8. Which of these is a pure compound?
A) Salt (NaCl)
B) Bronze
C) Sugar water
D) Air
E) Vinegar
9. Which of the following statements is true about pure substances?
A) They are always made of more than one phase
B) They can be separated by physical means
C) They have variable composition
D) They have definite physical and chemical properties
E) They consist of multiple visible parts
10. A mixture differs from a pure substance in that:
A) It has a constant boiling point
B) It cannot be separated
C) Its composition can vary
D) It is chemically combined
E) It contains only one element
11. Which is an example of a pure element?
A) Water
B) Bronze
C) Oxygen (O₂)
D) Vinegar
E) Sugar
12. Which process would not separate a pure substance?
A) Filtration
B) Electrolysis
C) Heating
D) Distillation
E) Crushing
13. A pure substance always:
A) Consists of molecules only
B) Contains two or more substances
C) Has uniform properties throughout
D) Is metallic
E) Can be seen only under a microscope
14. The boiling point of a pure substance is:
A) Variable depending on mass
B) Always the same at a given pressure
C) Irrelevant to its identity
D) Impossible to measure
E) The same for all substances
15. Which of these is a chemical change that occurs with a pure substance?
A) Freezing
B) Melting
C) Boiling
D) Rusting of iron
E) Dissolving sugar
16. Which of the following is always true about elements?
A) They contain at least two types of atoms
B) They can be separated into simpler substances
C) They are mixtures
D) They are pure substances
E) They have variable composition
17. Which of the following is a pure substance found in nature?
A) Ocean water
B) Soil
C) Oxygen gas
D) Lemonade
E) Milk
18. What distinguishes a compound from an element?
A) A compound contains atoms of one kind only
B) A compound can’t be broken down
C) A compound is physically mixed
D) A compound contains two or more types of atoms
E) A compound is always metallic
19. Which of these is not a compound?
A) CO₂
B) H₂O
C) O₂
D) NaCl
E) C₆H₁₂O₆
20. A pure substance cannot be:
A) A compound
B) An element
C) A mixture
D) A solid
E) A liquid
21. Which physical property is useful for identifying a pure substance?
A) Temperature
B) Boiling point
C) Size
D) Weight
E) Color
22. Which of the following is an example of a chemical compound?
A) Silver
B) Iron
C) Salt (sodium chloride)
D) Copper
E) Gold
23. Which of the following is the best description of a compound?
A) A mixture of two or more elements
B) A physical combination of substances
C) Two or more elements chemically bonded
D) A single element in pure form
E) A heterogenous substance
24. Which statement is true?
A) All pure substances are compounds
B) All mixtures are pure substances
C) A compound is always a pure substance
D) An element is not a pure substance
E) Pure substances cannot be solid
25. Which of the following is not a physical property of a pure substance?
A) Melting point
B) Boiling point
C) Density
D) Reactivity with acid
E) Color
26. Which of the following best differentiates a compound from a mixture?
A) Compounds are always gases
B) Mixtures have constant composition
C) Compounds are chemically combined
D) Mixtures can’t be separated
E) Compounds vary in composition
27. Distilled water is:
A) A mixture
B) A compound and a pure substance
C) An element
D) A homogeneous solution
E) A suspension
28. What happens when a pure compound is heated strongly?
A) It disappears
B) It melts and becomes a new element
C) It undergoes a chemical or physical change depending on the conditions
D) It becomes a heterogeneous mixture
E) It forms multiple phases immediately
29. A homogeneous mixture differs from a pure substance because:
A) It cannot be separated
B) It is uniform but has variable composition
C) It has a fixed composition
D) It always contains metal
E) It is made of only one element
30. The formula H₂O indicates that:
A) Water is a mixture of hydrogen and oxygen
B) Water contains two atoms of oxygen and one of hydrogen
C) Water is a compound and a pure substance
D) Water cannot be broken down chemically
E) Water is an element
Answers (in full text)
1. C) Matter with uniform and unchanging composition
2. D) Distilled water
3. C) A substance formed by chemical combination of two or more elements
4. C) Iron
5. C) Compounds and elements
6. B) Tap water
7. C) It has a fixed and definite composition
8. A) Salt (NaCl)
9. D) They have definite physical and chemical properties
10. C) Its composition can vary
11. C) Oxygen (O₂)
12. A) Filtration
13. C) Has uniform properties throughout
14. B) Always the same at a given pressure
15. D) Rusting of iron
16. D) They are pure substances
17. C) Oxygen gas
18. D) A compound contains two or more types of atoms
19. C) O₂
20. C) A mixture
21. B) Boiling point
22. C) Salt (sodium chloride)
23. C) Two or more elements chemically bonded
24. C) A compound is always a pure substance
25. D) Reactivity with acid
26. C) Compounds are chemically combined
27. B) A compound and a pure substance
28. C) It undergoes a chemical or physical change depending on the conditions
29. B) It is uniform but has variable composition
30. C) Water is a compound and a pure substance
- Questions on Chemical Symbols and Formulas
- Questions on Chemical Properties
- Questions on Reactants and Products
- Chemistry Questions with Answers Key.
Practical Classroom Applications
Share Social !
