Important questions with answers for the lessons
Is matter around us pure?
Matter in our surroundings.
Answers
Concept :
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★ This is Chapter 1 important Questions and answers.
★ Chapter name:- Matter in our surroundings.
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Question 1.
Is there any similarity in materials?
Answer:
Yes, all materials possess mass and occupy space.
Question 2.
When 50 g of sugar is dissolved in 100 mL of water, there is no increase in volume. What characteristic of matter is illustrated by this observation?
Answer :
This observation indicates that particles of water have spaces between them into which sugar particles fit.
Question 3.
What happens when an inflated air balloon is pricked with a pin? Name the property of the gaseous state exhibited by this observation.
Answer:
The balloon bursts and diffusion takes place.
Question 4.
Name the process which occurs when a drop of dettol is added to water.
Answer:
When dettol is added to water, diffusion takes place.
Question 5.
To which physical state of matter do the following statements apply?
(i) Incompressible, no fixed shape.
(ii) Compressible, no definite volume.
Answer:
- Liquid
- Gas
Question 6.
Name the state of matter in which:
(i) Layers of particles can slip and slide over one another easily.
(ii) Particles just move around randomly because of very weak force of attraction.
Answer:
- (i) Liquid state,
- (ii) Gaseous state.
Question 7.
Define density and give its SI unit ?
Answer:
Density of a substance is defined as the mass per unit volume. Its SI unit is kgm-³.
Question 8.
In which of the following, the particles have highest forces of attraction?
( Water, NaCl (solid), ice or, wax )
Answer:
NaCl (solid) has particles with the highest forces of attraction.
Question 9.
Why do the gases exert more pressure on the walls of the container than the solids?
Answer:
In gases, the particles move randomly at high speed and they collide with each other and with the walls of the container.
Question 10.
Can materials exist in all the three states?
Answer:
Yes, materials can exist in all the three states under different conditions of temperature and pressure.
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Concept :
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★ This is Chapter 2 important Questions and answers.
★ Chapter name:- Is matter around us pure ?
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Question 1.
How can you change a saturated solution to an unsaturated solution without adding any more solvent to it?
Answer:
By heating the saturated solution, it becomes unsaturated.
Question 2.
Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Answer:
It is a pure substance because chemical composition of sugar crystals is same irrespective of its source.
Question 3.
Based on which factor a solution is said to be diluted, concentrated or saturated?
Answer:
A solution is said to be diluted, concentrated or saturated on the basis of the amount of solute dissolved in the solution.
Question 4.
Identify solute and solvent in ‘tincture of iodine’.
Answer:
Iodine is the solute and alcohol is the solvent.
Question 5.
What is mass per cent of a solution?
Answer:
It is defined as the mass in grams of the solute present in one hundred grams of a solution.
Question 6.
What are the two components of a colloidal solution?
Answer:
The two components of a colloidal solution are dispersed phase and dispersing medium.
Question 7.
In what respect does a true solution differ from a colloidal solution?
Answer:
A true solution is homogeneous whereas a colloidal solution is heterogeneous.
Question 8.
Two liquids ‘A’ and ‘B’ are miscible with each other at room temperature. Which separation technique will you apply to separate the mixture of ‘A’ and ‘B’ if the difference in their boiling points is 27°C?
Answer:
We can separate two miscible liquids by fractional distillation, if both the liquids have difference in their boiling points. So, the mixture of liquids ‘A’ and ‘B’ can be separated by fractional distillation.
Question 9.
Define crystallisation ?
Answer:
It is a process that separates a pure solid in the form of its crystals from a solution.
Question 10.
Why is crystallisation technique considered better than simple evaporation to purify solids?
Answer:
Crystallisation is considered better than simple evaporation because :
- some solids decompose or get charred on heating to dryness.
- Some impurities may remain dissolved in the solution even after filtration.
- On evaporation, these contaminate the solid.