STD VII QUESTION BANK
CHEMISTRY
Chapter 1:Matter and its composition Q1.Name the following:
(a)The smallest unit of an element which may or may not have an independent existence- atom
(b)The force of attraction between similar kind of molecules -force of cohesion (c)Force of attraction between different kinds of molecules-force of adhesion (d)The space between the molecules -intermolecular space
(e)Force of attraction between the molecules -intermolecular force of attraction (f)Energy possessed by the molecules due to continuous motion -kinetic energy
(g)The state of matter in which atoms of gas break into positively and negatively charged particles -plasma
Q2.Rewrite the following statements by correcting the underlined word. (a)The intermolecular space is maximum in case of solids.
Ans-The intermolecular space is maximum in case of gases.
(b)Atom is the smallest unit of matter, which has an independent existence and can retain the physical and chemical properties.
Ans-Molecule is the smallest unit of matter, which has an independent existence and can retain the physical and chemical properties.
(c)The intermolecular force of attraction is minimum in solids. Ans-The intermolecular force of attraction is maximum in solids. Q3.Give reasons.
(a)Solids are hard and rigid.
Ans-Solids are hard and rigid because of the following reasons –
(i)The intermolecular space is minimum in solids as compared to liquids and gases. (ii)Because of the strong intermolecular forces of attraction in solids which binds the molecules together at a particular place.
(b)Gases are highly compressible.
Ans-(i) The intermolecular space is maximum in gases as compared to liquids and solids. (ii)The intermolecular force of attraction is negligible which makes the molecules free to move in the available space in all possible directions.
Therefore, gases are highly compressible.
(c)Liquids such as honey, ghee, oil are difficult to pour out.
Ans-Liquids such as honey, ghee, oil etc. are viscous and so there is more friction between the layers of molecules in these liquids.
Hence, they are difficult to pour out. Q4.Fill in the blanks.
(a)The matter in the sun is in _____state. Ans -plasma
(b)The intermolecular force of attraction _____ if the intermolecular space between the molecules decreases.
Ans-increases
Q5.Differntiate between on the basis of what is mentioned in the brackets. (i)Solids and gases (density)
Ans-Solids Gases
Density is generally high. Density is low as compared Liquids and gases.
ii. Liquids and gases (compressibility)
Ans-Liquids Gases
They are slightly compressible. Highly compressible. Q6.Classify the following as solids, liquids and gases.
Ice, water ,nitrogen ,sulphur dioxide, bromine , carbon . Ans: solids-ice, carbon
Liquids -Water, bromine
Gases -nitrogen , sulphur dioxide
CHAPTER 2: PHYSICAL AND CHEMICAL CHANGES Q1.Name the following.
(a)The process by which a solid changes into a liquid-melting
(b)The fixed temperature at which a solid changes into liquid at atmospheric pressure - melting point
(c)The process by which a liquid changes into gas -boiling
(d)The fixed temperature at which a liquid changes into gas at atmospheric pressure - boiling point
(e)The process by which a gas changes to liquid on cooling -condensation (f)The change involving absorption of heat energy -endothermic change
(g)The change involving evolution or release of heat energy -exothermic change
Q2.Correct the following incorrect statements by replacing the underlined word . (a)Cooking of food is an exothermic change .
Ans-Cooking of food is an endothermic change .
(b)Dissolution of ammonium chloride is an exothermic change . Ans-Dissolution of ammonium chloride is an endothermic change. (c)Magnesium ribbon burns with a blue flame .
Ans-Magnesium ribbon burns with a dazzling white flame . (d)Candle burns to produce sulphur dioxide and water vapour . Ans -Candle burns to produce carbon dioxide and water vapour . Q3.Fill in the blanks .
(a)Solar energy is converted into chemical energy during____________. Ans-photosynthesis
(b)A lot of heat is usually off or absorbed during a _______change . Ans-chemical
(c)Sugar on heating forms carbon and ______. Ans-steam
Q4.Differntiate between the following pairs on the basis of the criteria given in brackets . (a)Physical and chemical change
(i)Involvement of energy (ii)formation of new substance
Ans-(i)Physical change Chemical change There is no net absorption or There is always net Release of energy . absorption or release of Energy .
(ii)No new substance is formed . (ii)New substance is Formed .
(b)boiling and boiling point (definition )
Ans-Boiling Boiling point
The process of changing of a The fixed temperature at Liquid into gas is called boiling. Liquid changes into gas at Atmospheric pressure Is called boiling point.
Q5.Write your observation for the following.
(a)Magnesium ribbon is burnt in air .
Ans-When magnesium ribbon is burnt in air /oxygen ,it burns with a brilliant white flame producing a large amount of heat and light .
(b)Heating of mercuric oxide in a test tube .
Ans-When mercuric oxide is heated ,red colour of mercuric oxide changes to black .Also tiny silvery droplets appear on the cooler parts of the test tube .
Q6.Give reasons.
(a)Heating of zinc oxide is a physical change .
Ans-On heating ,white zin oxide changes to yellow colour and on cooling ,it again turns back to white.Since no new substance is formed ,it is a physical change .
(b)Burning of candle is a chemical change .
Ans-Burning of candle is a chemical change because it forms two new products i.e carbon dioxide and water vapour.
(c)Heating of sugar is a chemical change .
Ans-The products formed during heating of sugar i.e carbon and water vapour cannot be recombined to form sugar .
Hence ,it is a chemical change .
(d)When iron becomes rust ,its weight increases .
Ans-Iron becomes rust when it reacts with oxygen of air to form iron oxide .The extra oxygen adds up to the increase in weight .
Q7.Identify the type of change .(Physical /Chemical ) (i)Melting of butter -physical change
(ii)Formation of fog , mist etc -physical change
(iii)Fermentation of sugar solution to alcohol -chemical change (iv)moulding of glass by heat -physical change
(v)blackening of silver ware -chemical change (vi)lighting of match stick -chemical change CHAPTER 4: ATOMIC STRUCTURE
Q1.Give a scientific term for the following .
(a)The smallest unit of a pure substance that has an independent existence and can retain all the physical and chemical properties of that substance -molecule
(b)The number of atoms constituting one molecule of a compound -atomicity (c)The path along which electrons revolve -orbit /shell
(d)The collection of protons and neutrons present in the nucleus of an atom -nucleons (e)Elements which possess the properties of both metals and non-metals -metalloids (f)The horizontal rows in the periodic table -periods
(g)The vertical columns present in the periodic table – groups (h)The outermost shell of an atom- valence shell
(i)The higher valency of iron -ferric Q2.Fill in the blanks .
(a)The nucleus of an atom carries positive charge .
(b)The mass of an electron is 1/1837th times the mass of a proton . (c)The nucleus of Helium has two protons .
(d)Atomic number is equal to the number of protons .
(e)The maximum number of electrons in the second orbit is 8.
Q3.Rewrite the false statements by correcting the underlined words . (a)Chromium forms bivalent electropositive ions .
Ans-Chromium forms trivalent electropositive ions . (b)Metals have a tendency to gain electrons .
Ans- Non -metals have a tendency to lose electrons . (c)Phosphorus is tri-atomic.
Ans-Phosphorus is tetra -atomic . Q4.Give reasons.
(a)An atom is electrically neutral .
Ans-An atom is electrically neutral as the number of protons present inside the nucleus is equal to the number of electrons revolving around the nucleus i.e the number of positive charge is equal to the number of negative charge .
(b)Negatively charged electrons do not fall into the nucleus .
Ans-Negatively charged electrons revolve in in fixed orbits at a fixed speed and is counter balanced the centrifugal force that balances the pull of the nucleus .
Hence, they do not fall into the nucleus .
Q5.Differntiate between on the basis of what is mentioned in the brackets.
(i)Atom and molecule (nature of existence )
Ans-Atom Molecule
May or may not have an independent Always exists independently . Existence .
(ii)Protons and neutrons (type of charge )
Ans-Protons Neutrons
They carry positive charge . They carry no charge. Q6.Write the common names for the following .
(a)sodium carbonate -washing soda (b)sodium bicarbonate -baking soda (c)sodium chloride -common salt (d)copper sulphate -blue vitriol
(e)calcium carbonate -limestone/chalk Q7.Answer the following .
(a)An element X has 2 electrons in its valence shell and element Y has 5 electrons its valence shell .Without identifying the original element :
(i)Identify the metal and non -metal among X and Y . Ans-Metal-X , Non-metal -Y
(ii)Write the valency of X and Y .
Ans-The valencies of X and Y are : X =2 and Y =3 (8-5=3) (iii)Write the chemical formula formed between X and Y . Ans-X3Y2
(b)Write the importance of periodic table .
Ans-(i)It determines the atomic number of an element . (ii)It gives information about the periodicity of elements.
(iii)Gives information about the same number of valence electrons in a group . CHAPTER 5: LANGUAGE OF CHEMISTRY
Q1. Name the following :
(a)A reaction that takes place when two or more reactants come in close contact - chemical reaction
(b)The precipitate formed when lead nitrate reacts with potassium iodide -lead iodide (c)Chemical reactions which proceed with release of heat energy -exothermic reactions (d)The reddish brown gas evolved by heating lead nitrate -nitrogen dioxide
(e)The colour of the oxide formed on heating of copper carbonate-black
(f)The chemical reactions taking place with the absorption of heat energy-endothermic reactions
(g)Substances taking part in a chemical reaction-reactants (h)Substances formed as a result of chemical reaction-products Q2.Give two examples for each of the following.
(a)Coloured precipitates-lead iodide, ferrous hydroxide
(b)Colourless gases-oxygen, hydrogen, nitrogen , hydrogen , carbon dioxide
(c)Coloured metal oxides-lead monoxide, copper oxide lead dioxide,red lead oxide (d)Colourless precipitates -silver chloride, barium sulphate
Q3 .State one relevant observation for the following . (a)Lead nitrate is heated strongly .
Ans-When lead nitrate crystals are heated strongly , white crystals of lead nitrate changes to yellow colour . Also a reddish brown gas is evolved .
(b)Copper sulphide is treated with hydrochloric acid .
Ans-A colourless gas with the smell of rotten egg is evolved . (c) Heating of copper carbonate .
Ans-When copper carbonate is heated , the green colour changes into black colour . (d)Silver nitrate is treated with sodium choride .
Ans-A white precipitate is formed when silver nitrate is treated with sodium chloride . (e)Magnesium ribbon is heated strongly .
Ans- When Magnesium ribbon is strongly heated it burns with a dazzling white flame. Q4. Write balanced chemical equations for the following reactions .
(a)Reaction between carbon and vapours of sulphur . Ans- C (s) +2S (g)---→ CS2(l)
(b)Reaction between sodium sulphide and hydrochloric acid . Ans- Na2S (g) + 2HCl ---→2NaCl + H2S
(c)Reaction between quicklime and water . Ans- CaO + H2O ---→Ca(OH )2 + heat energy (d)Reaction between hydrogen and oxygen. Ans - 2H2(g) + O2(g) ---→ 2H2O (l)
(e)Reaction between limewater and carbon dioxide . Ans - Ca(OH )2 + CO2 ---→CaCO3 + H2O
CHAPTER 6 : METALS AND NON-METALS Q1.Name the following .
(a)The property by which metals can be beaten into sheets -malleability
(b)The property of producing ringing sound by metals when struck hard -sonority (c)A metal which is a poor conductor of electricity -bismuth , tungsten
(d)Soft metals-potassium ,sodium
(e)A metal having low boiling point -mercury
(f)A metal which is non-malleable -zinc ,arsenic, antimony (g)A liquid non-metal -bromine
(h)A non-metal which is solid at room temperature -carbon , sulphur , phosphorus , silicon (i)A non-metal which is highly tensile-C60
(j)A non-metal which is a good conductor of electricity -graphite (allotrope of carbon) (k)A metal which is lighter than water -sodium, potassium
(l)The property by which a substance can be drawn into wires -ductility (m)A metal having low tensile strength -zinc, arsenic , antimony
Q2.Differntiate the following on the basis of the criteria mentioned in brackets . Metals and Non-metals
(i)Malleability (ii)tensile strength (iii)state
(iv)ductility
Ans: Metals Non-metals
(i)Metals are generally malleable. (i)Generally non-malleable. (ii)Have high tensile strength . (ii) Lack tensile strength . (iii)Generally solid at room temperature . (iii)Generally gases at Room temperature .
(iv)Generally ductile . (iv)Non-ductile.
