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Science Do as instructed[5 M]

Elements, Compounds and Mixtures · Maharashtra Board STD 7 (MSBSHSE - English Medium). 3 questions.

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Do as instructed[5 M]

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3 questions · self-marked practice — reveal the answer and mark yourself.

Question 15 Marks
Write short notes on:
(1) Distillation (2) Sublimation (3) Magnetic separation (4) Sedimentation (5) Filtration (6) Evaporation
Answer
1. Distillation: It is a process of heating a solution containing soluble solids to form vapours of the liquid and then cooling the vapours to get the liquid back. e.g. A mixture of common salt and water is taken in distillation flask and heated. Steam rises up and comes out into condenser.

2. Sublimation: It is a process in which some solids on heating are transformed directly to vapour without passing through the liquid state, (i) It is used to separate a mixture of solids. The vapours are cooled separately, (ii) Used to separate ammonium chloride, iodine, camphor and sulphur from any mixture.

3. Magnetic separation: A mixture with iron fillings as one of the components can be separated using magnet to attract the iron particles away from the mixture.

4. Sedimentation: (i) It is a process of separating an insoluble solid from a liquid in which it is suspended, by allowing it to settle to the bottom of the container, e.g. Muddy water contains heavier particles like sand and soil, (ii) Leave this muddy water undisturbed for some time, (iii) The heavier soil and sand particles settle down and the clear upper water is poured out by decantation.

5. Filtration: It is used for separating insoluble solids from a liquid, e.g. mixture of chalk and water is poured through a filter paper in a funnel while the water gets collected in the beaker below, chalk is retained in the filter paper.

6. Evaporation: It is used for recovering dissolved solid substances from solutions by evaporation e.g. sugar can be recovered from sugar-water.

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Question 25 Marks
From the internet or reference books obtain information about elements and prepare a table according to the format given below:
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Question 35 Marks
1.Take sugar in a test tube and heat the test tube. Observe what happens. What remains behind?
2.Using tongs hold a magnesium ribbon in a flame and observe what changes took place?
3.What does the name carbon dioxide imply – how many and which elements is this substance made of?
4.Which of these are compound, which are elements?
5.What is the smallest particle of a compound called?
Answer
1.When a test tube containing sugar is heated, the sugar melts and then it loses water leaving behind a black substance. This black substance is carbon.
Sugar is sucrose, a molecule of sugar is composed of 12 atoms of carbon, 22 atoms of hydrogen and 11 atoms of oxygen. $\left( C _{12} H _{22} O _{11}\right)$.
  1. Sugar is a compound made from these three elements carbon, hydrogen, oxygen.
  2. It is a Carbohydrate.

2.When a magnesium ribbon is ignited, light and heat are produced. Magnesium reacts chemically with oxygen in the air
$2 Mg_{(s)}+O_{2(g)} \rightarrow 2 MgO_{(s)}$
Magnesium oxide is produced.
3.
  1. Carbon dioxide is a compound. It is a tasteless, odourless gas. It is a natural product of respiration.
  2. Plants use this to produce food.
  3. Humans breath out the $CO _2$.
[A molecule of the compound carbon dioxide contains one atom of the element carbon and two atoms of the element oxygen.]
4.
  • Water $\rightarrow$ compound $H _2 O$ (hydrogen + oxygen), Oxygen $\rightarrow$ Element
  • Carbon dioxide $\rightarrow$ compound $CO _2$ (Carbon + Oxygen)
5.The smallest particle of a compound is called molecule.
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