CBSE Class 9 - Chemistry - CH2 - Is Matter Around Us Pure? (Short Q and A)

Is Matter Around us pure?

Short Q & A

Simple Distillation Technique.
Can you name the labelled parts? See answer at wikimedia

Q1: Who was the first scientist to use the term 'element'?

Answer: Robert Boyle was the first scientist to use the term element in 1661.


Q2: Name the chemist who for the first time, defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Answer: Antoine Laurent Lavoisier (1743-94), a French chemist


Q3: Who is known as the father of Modern Chemistry?

Answer: Antoine Laurent Lavoisier (1743-94), a French chemist


Q4: Do physical changes alter the identity of a substance?

Answer: No.




Q5: Do chemical changes alter the identity of a substance?

Answer: Yes


Q6: Why is copper found in electrical wires considered metal element?

Answer: Copper has the same composition and properties wherever it is found. Thus, copper is a pure substance and is a chemical element. Copper has lusture, a good electrical conductor and is ductile. It is a metal element.


Q7: What is a pure substance or a chemical?

Answer: A pure substance or a chemical is any substance that always has the same composition and properties wherever it is found.


Q8: Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air.

Answer: Ice, Iron, Hydrochloric acid, Calcium Oxide, Mercury are examples of 'pure substance'.

(Note: Few teachers categorize ice as a homogeneous mixture of water and minerals while others consider it pure substance consisting of water molecules.)


Q9: Identify pure substance, homogeneous mixture and heterogeneous mixture in the following list:

(a) air
(b) copper in copper wire
(c) milk
(d) water
(e) Nitrox scuba tank (used by scuba divers to inhale oxygen)
(f) An ice-cream shake
(g) A piggy bank containing 10p and 20p and one-rupee coins

Answer: Pure Substance: copper, water
Homogeneous Mixture: air, Nitrox tank
Heterogeneous: Milk, Ice-cream shake, Piggy Bank


Q10: Identify physical or chemical changes in the following:

(a) Melting of iron metal
(b) Rusting of iron
(c) Burning of wood
(d) Sawing of wood
(e) dissolving sugar in water
(f) Black graiy coating on silver utensil
(g) Fireworks

Answer: (a), (d), (e) are examples of physical changes
        (b), (c) (f) and (g) are examples of chemical changes


Q11: Classify each of the following as an element, a compound, or a mixture: 

(a) carbon in pencils
(b) tin in soda cans
(c) Carbon Dioxide we exhale
(d) Copper in copper wires
(e) Mango Juice
(f) Soil

Answer: Elements: Carbon, Copper, Tin
Compound: Carbon Dioxide
Mixture: Mango Juice, Soil


Q12: Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?

Answer: Crystallization


Q13: What happens when a saturated solution is carefully cooled?

Answer: It will become a super saturated solution which further leads to formation of crystals of solute (crystallization)


Q14: A cold drink glass bottle when refrigerated does not show any bubble formation. However when we take out the bottle and open it, bubbles starts forming up. Why?

Answer: Solubility of gas (here Carbon DiOxide) decreases with increase in temperature. When we open the refrigerated bottle, it warms and thus CO2 gas bubbles start escaping the drink.