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The City School

Comprehensive Worksheet December 2016

ScienceClass 7

(Answering Key)

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Q-1: Choose and encircle the most suitable answer. [ /20 marks]

1. Spore plant2. Carl Linnaeus3. Sea horse and eel4. Dichotomous key5. Compounds6. Silicon and oxygen7. Solute8. Bromine9. ink10. Boron11. Distillation12. Good conductor of electricity13. Decreases14. Sun15. Zero16. Density17. 19.3 g/cm318. All of the above19. Friction20. Star

Q.2- Give scientific reasons for the following. [ /10 marks]

i. Earth’s gravity pulls everything towards its centre, so it needs a lot of force to get out and awayfrom the gravity.

ii. Sun, Earth and Moon do not lie in the same plane or they are not in a line.

iii. Salt is completely dissolved in water, its amount is same everywhere in the solution. iv. Conifers have seeds not in fruits but enclosed in cones.v. Pollutant or dangerous gases from the atmosphere get dissolved in the rain water and make it

acid rain.

Q.3. Are the following statements true or false? Correct them if they are false [ /10 marks]

i. False. Some gases are compounds e.g. carbon dioxide. ii. True

iii. False. It ranges from 8-14iv. False. Invertebrates with jointed legs are called as arthropods. v. False. The amount of matter in an object is called as its mass. vi. True

vii. False. As temperature increases the solubility of gases decreases.

viii. False. A compound can be broken down into simpler substances by chemical reactions. ix. False. Red litmus paper remains red in acids and alkaline solutions.x. False. Vascular plants have xylem and phloem for transferring water and food around the plant.

Q.4- (a) Give one word answer. [ /5 marks]

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i. Carbon dioxide

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ii. Aqueous solution iii. Boiling pointiv. Oxygen v. Up thrust

Q.4-(b) Write down the use of the following. [ /5 marks]

i. Helium : lightest gas, used to fill balloonsii. Indicator: used to indicate whether a substance is acid, alkali or neutral and also finds the strength

of the substance.iii. Fractional distillation: to separate substances with different boiling points, from a mixture. iv. Solid- solid mixture: used to make alloys e.g. steelv. liquid nitrogen: used as a cooling agent

S UB JECTIVE [ /50 ma rks]

Q.1.(a) Define neutralization. [ /1 mark]

Acid and alkali mixed together in proper amount neutralize each other, neutral solution of a salt and water is formed. pH value of that solution is 7.

(b) Describe some uses of neutralization. [ /2 marks]

i. To neutralize an acid or alkali if it is spilt on our skin.ii. An acid is produced in our mouth when bacteria decay the food particles stuck in between our teeth.

Tooth pastes are made to be slightly alkaline and are used to neutralize that acid.iii. When soil becomes too much acidic due to acidic rain, an alkali called calcium oxide is added to

that acidic soil to make it neutral.iv. When soil becomes too much alkaline, animal manure (animal manure is acidic) is added to that

soil in order to make it neutral.v. Acidic bee sting can be made less painful by neutralizing it with an alkali like

soap. vi. Alkaline wasp sting can be neutralized with an acid e.g. lemon juice or vinegar

vii. Excess of stomach acid causes acidity or burning. Ant acids (in form of tablets or syrups whichcontain an alkali magnesium hydroxide in them) can be used to neutralize excessive acid in the stomach to give relief in stomach acidity.

(c) Write three similarities between acids and alkalis. [ /3 marks]

i. Both acids and alkalis are good conductors of electricity.ii. Both acids and alkalis react with each other and make a neutral solution.

iii. Both strong acids and alkalis are corrosive ( means if they are strong they can burn our skin and other living tissues)

.

(d) List down three differences between acids and alkalis. . [ /3 marks]

Acids AlkalisHave pH value less than 7 Have pH value more than 7Have a sour taste Have a bitter tasteTurn blue litmus paper to red. Turn red litmus paper to blue.

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Strong acids are called as corrosive Strong alkalis are called as causticReact with metals and produceHydrogen gas

-

React with carbonates and produceCarbon dioxide gas

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(e) Which gas is produced when; [ /1 mark]

Dilute acids react with metals; h y d r o g e n gas Dilute acids react with carbonates. Carb on d ioxid e gas

Q.2. (a) Name the celestial bodies in the Universe. [ /2

marks] Star (Sun), moon planets, galaxies, asteroids

(b) Name two optical instruments which can be used to help us observe celestial bodies. [ /2 marks]

Telescopes binoculars,

(c) Why is the Earth able to support a diversity of life forms? . [ /2 marks]

Earth has these characteristics to support life: An atmosphere, so it has air and oxygen Liquid water Suitable temperature Solid surface to live on

(d) Differentiate between the solar eclipse and lunar eclipse. [ / 4 marks]

The solar and lunar eclipses happen when the Sun, Earth and Moon come in a line. As they all are not on the same plane (means these objects are not on the same line or same level), so these eclipses do not happen so often.

Solar eclipse Lunar eclipse

During solar eclipse the Sun is partially or totallyblocked by the moon.

During lunar eclipse the moon is blocked by theEarth.

This happens when the Sun, Earth and moon are in aline and the moon comes in between the Sun and theearth.

This happens when the Sun, Earth and moon are in aline and the earth comes in between the Sun and themoon.

In this eclipse the Sun casts a shadow of the moon on the earth.

In this eclipse the Sun casts a shadow of the earth on the moon.

During a total solar eclipse the day turns dark andthe temperature drops.

This eclipse occurs on nights when there is a fullmoon.

Q3. (a) Define density. [ /1 mark]

The amount of mass in certain volume is called as density of that substance.

(b) A stone sinks in water, while a piece of wood floats. Which one of them has a higher density? [ /1 mark]

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Stone

(c) .Which state of matter has the highest and which state has the lowest density? [ /1 mark]

Solids have the highest density – Gases have the lowest density.

(d) Which liquid has the highest density? [ /1 mark]

Mercury

(e) Define friction. Give some advantages and disadvantages of friction. [ /2+2+2=6

marks] A type of force produced when two surfaces rub against each other.

Advantages: Friction helps us tie our shoe laces, stop moving vehicles, make fire, stitching in our clothes stays in due to friction. e.t.c

Disadvantages: Unnecessary heat or fire are produced, hinders the movement of objects, slows down moving objects, our knees get hurt when we fall down e.t.c

Q.4 (i) Give similarities between hydrogen, oxygen and carbon dioxide gas. [ /3

marks] All these gases are:

Colourless Odourless tasteless

(b) Give differences between hydrogen and carbon dioxide gas. [ /3 marks]

Hydrogen Carbon dioxideIt can burn It extinguishes( stops/ puts out) fire

It is lighter than air It is heavier than air

It burns with a squeaky pop sound. It turns lime water into milky white colour

(c) During a chemical reaction a gas was produced, how can we test [ /2 marks]

i. If it was hydrogen gas: If the gas burns with a squeaky pop sound it is hydrogen gas.ii. If it was carbon dioxide gas: If we add that gas to some lime water and the lime water

turns milky white then surely the gas is carbon dioxide gas. Only carbon dioxide can turn lime water to milky white. This test is called as Lime water test.

Q.5. (a) Which difference in property of the constituents of mixtures is used to separate them in thefollowing separation techniques? [ /2 marks]

i. Filtration

This technique is used to separate an insoluble solid from a

mixture. ii. Evaporation

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This technique is used to get a soluble solid from a mixture /

solution. iii. Fractional distillation

This technique is used to separate substances with different boiling points from a

mixture. iv. Chromatography

This technique is used to separate different solutes from a mixture / solution .e.g. ink

v. State the properties of compounds. [ /2 marks] Compounds are formed by chemical reactions Compounds can only be broken down into simpler substances by chemical reactions. A compound has different properties that are different from the properties of its const ituent elements. The different elements in a compound are joined together in a fixed proportion.

vi. List down various methods of forming compounds. [ /1

mark] Compounds can be formed by

Combining two elements together Combining two compounds together Combining an element and a compound together

vii. Sort out these substances into:

Strong acids weak acids

[ /1 mark]

Car battery, orange, grape fruit, kiwi fruit, vinegar, apple, tomato sauce

Salad cream, lemon

viii. Sort out these substances into: : [ /1mark]

Strong alkalis weak alkalis

Washing powder, bleach baking soda, tooth paste, Rennie indigestion

tablets, Soap

ix. Write down any two names of strong acids. [ /1 mark]

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x. Write down any two names of strong alkalis. [ /1 mark]

xi. Write down two uses of acids and two uses of alkalis in our daily life. [ /2

marks] Uses of acids: car battery, many foods contain acids, for cleaning rust e.t.c

Uses of alkalis: antacids, medicines, used in paint industry and in formation of glass, present in our vegetables e.t.c

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(b) Name the metalloids from the Periodic Table.

(1) (2) (3) (4)

(5 ) (6) (7 )