Vidaara.orgClass 9 · Chemistry
CodeVID-C9-02-T3-01
Assignment — Physical & Chemical Changes; Elements, Compounds & Mixtures
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Which is a physical change?
- A.Burning of paper
- B.Souring of milk
- C.Melting of ice
- D.Cooking of food
2.
An element that conducts electricity and is malleable is a:
- A.non-metal
- B.metal
- C.compound
- D.mixture
3.
Silicon is an example of a:
- A.metal
- B.non-metal
- C.metalloid
- D.compound
4.
The formula of iron sulphide formed in the iron and sulphur experiment is:
- A.Fe2S
- B.FeS
- C.FeS2
- D.Fe2S3
5.
Which has a fixed composition by mass?
- A.Air
- B.Sea water
- C.A compound
- D.Soil
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
State two differences between a physical and a chemical change.
7.
List three properties of metals.
8.
Give one example each of a chemical change shown by gas evolution and by a colour change.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Compare a compound and a mixture on the basis of composition, properties and method of separation.
10.
Distinguish between metals, non-metals and metalloids with one example each.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the iron and sulphur experiment. Explain how it demonstrates the difference between a mixture and a compound, listing the observations before and after heating.
Answer Key
Section A — Multiple Choice Questions
- (C) Melting of ice
- (B) metal
- (C) metalloid
- (B) FeS
- (C) A compound
Section B — Short Answer (2 marks)
- A physical change forms no new substance and is usually reversible (e.g. melting); a chemical change forms a new substance and is hard to reverse (e.g. rusting).
- Metals are lustrous (shiny), good conductors of heat and electricity, and malleable/ductile (some are also sonorous).
- Gas evolution: a metal reacting with dilute acid releasing hydrogen. Colour change: iron turning reddish-brown on rusting.
Section C — Short Answer (3 marks)
- A compound has a fixed ratio by mass, new properties unlike its elements, and is separated only by chemical means. A mixture has a variable composition, keeps the properties of its components, and is separated by physical methods.
- Metals are lustrous, good conductors and malleable (e.g. copper); non-metals are dull, brittle and poor conductors (e.g. sulphur); metalloids show in-between properties (e.g. silicon).
Section D — Long Answer (5 marks)
- Iron filings and sulphur powder are first mixed. In this mixture a magnet pulls out the iron, the yellow sulphur is still visible, and dilute acid gives an almost odourless gas — each element keeps its own properties, so it is a mixture. When the mixture is heated strongly, it glows and forms a black solid, iron sulphide (FeS). Now a magnet does not attract it, the colour is uniformly black, and dilute acid produces a foul-smelling gas (hydrogen sulphide). Because a new substance with new properties has formed by chemical combination in a fixed ratio, the heated product is a compound. This contrast — separable by magnet versus not, two colours versus one, no energy change versus heat needed — is exactly how a mixture differs from a compound.
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