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CHEMISTRY [5 Mark Question Answer]

Elements, Compounds and Mixtures · ICSE STD 8 (ICSE - English Medium). 6 questions.

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[5 Mark Question Answer]

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6 questions · timed · auto-graded

Question 15 Marks
State four differences between compounds and mixtures.
Answer
Compound
  1. A compound is formed from its constituent elements as a result of chemical reaction.
  2. A compound is always homogeneous in nature.
  3. In a compound the elements are present in a fixed ratio by weight.
  4. The components of a compound can’t be separated by physical methods but can be separated by chemical methods only.
  5. The properties of a compound are different from those of its elements.
  6. The formation of a compound from its elements is accompanied by energy changes.
Mixture
  1. A mixture is obtained form its $($elements, compounds$)$ components as a result of physical change.
  2. The mixtures can be homogeneous or heterogeneous.
  3. In a mixture the components can be present in any ratio.
  4. The components of a mixture can be separated by physical methods only.
  5. The properties of a mixture lie between those of$-$its components.
  6. The formation of a mixture from its constituents is not accompanied by energy changes.
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Question 25 Marks
Why is it necessary to separate the constituents of a mixture.
Answer
Because: The mixtures contain unwanted substances which may be harmful and may degrade the properties of mixtures. So we, need to separated them and extract useful substances.
This is necessary because
$(i)$ It removes unwanted and harmful substances
$(ii)$ to obtain pure and useful substances them.
Example : Sea water is rich in common salt which is an important ingredient of our food to add taste and nutrients. But sea water, cannot be directly used to get the salt.
Hence, it is necessary to separate both.
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Question 35 Marks
Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method. Chalk powder from water
Answer
Technique used to separate chalk powder from water is filtration.
Reason $–$ Because this process is used to separate the components of a heterogeneous solid$-$liquid mixture in which solids are lights and insoluble in liquids. Substances used as filters are sand filter paper at These filters allows the liquid to pass through them, but not solids.
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Question 45 Marks
Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method. Salt from sea water
Answer
The technique used to separate the salt from seawater is Evaporation.
Reason $–$ Because this method is used to separate the components of the homogeneous solid$-$liquid mixture. In this method, sea water is collected in a shallow bed and allowed to evaporate in the sun. When all the water is evaporated, salt is left behind. By this method, we only get solid and liquid is evaporated in its vapour form.
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Question 55 Marks
Classify the following substances into compounds and mixtures:
Answer
Carbon dioxide, air, water, milk, common, salt, blood, fruit juice, iron sulphide.
Carbon dioxide $— ($Compound$)$
air $— ($Mixture$)$
water $— ($Compound$)$
milk $— ($Mixture$)$
common salt $— ($Compound$)$
blood $— ($Mixture$)$
fruit juice $— ($Mixture$)$
iron sulphide $— ($Compound$)$
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Question 65 Marks
Differentiate between: pure and impure substances
Answer
Pure substances $—$
  1. Pure substances have definite composition and definite physical and chemical properties.
  2. They are all homogeneous i.e. their composition is uniform throughout the bulk.
  3. Examples : Elements and compounds.
Impure substances $—$
  1. Impure substances are made up of two or more pure substances mixed together in any proportion.
  2. They may be homogeneous or hetergeneous i.e. their composition is not uniform throughout the bulk.
  3. They are all mixtures.
    Examples : air, sea water, petroleum, a solution of sugar in water are all impure substances.
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[5 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip