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CHEMISTRY [3 Mark Question Answer]

Matter · ICSE STD 8 (ICSE - English Medium). 4 questions.

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[3 Mark Question Answer]

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4 questions · timed · auto-graded

Question 13 Marks
Give reasons When magnesium is burnt in air, there is an increase in mass after the reaction.
Answer
When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is more than the mass of magnesium.
This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.
$\underset{\text { (magnesium) }}{2 \mathrm{Mg}}+\underset{\text { (air) }}{\mathrm{O}_2} \longrightarrow \underset{\text { magnesium oxide }}{2 \mathrm{MgO}}$
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Question 23 Marks
What are the three states of matter ? Define each of them with two examples.
Answer
The three states of matter are solids, liquids and gases :
Solids - A solid has a definite shape and definite volume.
Example – wood, stone, iron, ice etc.
Liquid - A liquid has a definite volume but not definite shape.
Example - water, juice, milk, oil, etc.
Gases - A gas neither has definite shape nor a definite volume.
Example - air, hydrogen, oxygen, watervapour etc.
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Question 33 Marks
Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
Answer
The particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces.
But the strength of inter$-$molecular force of attraction is very strong in coal, therefore it is not possible to break them into small pieces.
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Question 43 Marks
What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
Answer
When a gas jar full of bromine vapours $($reddish brown$)$ is inverted over a gas jar containing air over it. It is observed that after sometime, the reddish brown vapours of bromine also spread out into the upper jar. This mixing is called diffusion. The rate of diffusion is the fastest in gases and the slowest in solids. It increases with an increase in temperature.
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[3 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip