1. Give an example of a metal which
(i) is a liquid at room temperature.
(ii) cart be easily cut with knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Ans. (i) Mercury (Hg)
(ii) Sodium and potassium
(iii) Silver and copper
2. Explain the meanings of malleable and ductile.
Ans. A metal is said to be malleable if it can be beaten into thin sheets, e.g. silver and gold are the best malleable metals.
Ductile: A metal is said to be ductile when it can be drawn into thin wires, e.g. silver and gold are the best ductile metals.
3. Why is sodium kept immersed in kerosene oil?
Ans. Sodium is highly reactive metal. It reacts with oxygen in the air at room temperature and catches fire. To prevent this, sodium which does not react with kerosene. kept preserved under kerosene.
4. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Ans. When a reactive metal reacts with hydrochloric acid, Metal Chloride and hydrogen gas are produced. A reactive metal displaces the hydrogen from acid and releases hydrogen gas.
7. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Ans. Zinc is more reactive than iron, hence when added to iron (II) sulphate, it can displace iron metal and the colour of solution fades from green to colourless due to the formation of zinc sulphate.
8. (i) Write the electron dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons
(iii) What are the ions present in these compounds?
9. Why do ionic compounds have high melting points?
Ans. Ionic compounds are made up of two oppositely charged ions i.e., cations (+) and anions (-), which are held together with a strong electrostatic force of attraction. To break this strong bonding into ions, a large amount of heat energy is required, hence the melting point of ionic compounds is high.
10.Define the following terms:
(i) Mineral (ii) Ore (iii) Gangue
Ans. (i) Mineral: These are naturally occurring chemical substance which, contains metals with, some other elements: or impurities.
(ii) Ore: The minerals from which metals can be extracted economically on large scale are called ores.
(iii) Gangue: The impurities present in ore/minerals are called gangue.
11. Name two metals which are found in nature in the free state.
Ans. Gold, platinum (and silver).
12. What chemical process is used for obtaining a metal from oxide?
Ans. To obtain metals from its oxides for metals of medium reactivity one can use carbon as a reducing agent and the chemical process is called reduction.
14. Which metals do not corrode easily?
Ans. Metals which are less reactive and lie at the bottom of reactivity series i.e., silver, gold, platinum do not corrode easily.
15. What are alloys?
Ans. Alloys are a homogeneous mixture of two or more metals or metals or metals and non-metals having a definite composition of the mixture.
1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal (b) MgCI2 solution and aluminium metal
(c) FeSO4 solution and silver metal (d) AgNO3 solution and copper metal
Ans. (d) AgNO3 solution and copper metal
2. Which of the following methods is suitable for preventing an iron frying pan from, rusting?
(a) Applying grease (b) Applying paint
(c) Applying a coating of zinc (d) All of. the above.
Ans. (c) Applying a coating of zinc
3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. This element is likely to be
(a) calcium (b) carbon (c) silicon (d) iron
Ans. (a) Calcium.
4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier then tin. (b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin (d) zinc is less reactive than tin.
Ans. (c) zinc is more reactive than tin.
5. You are given a hammer, a battery, a bulb, wires and switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Ans. (a) To distinguish between samples of- metals and non-metals one can use the hammer to beat the given material into sheets if it breaks it is non-metal. but if it is flattened then it is a metal.
One can also use battery, wires, bulb and switch to make a circuit and use the given material to complete the circuit one by one if the electric current flows and the bulb glow then it is metal and if not then it is non-metal.
(b) Because of malleable character, metal like iron can be hammered into a thin sheet which is used as a tin sheet, box surface, to prepare bucket, pan etc.
Metals are a good conductor of electricity which property is used to prepare electrical wire of aluminium and copper in an electric circuit.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans. The oxides which behave as acid, as well as a base, are called amphoteric oxides e.g., Al2O3 and ZnO are amphoteric oxides; they both react with acid as Well as a base to give salt and water.
7. Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Ans. Metals which lie above Hydrogen in the activity series ie. Zn, Al, Mg can displace hydrogen from dilute acids because they are more reactive than. Metals which lie below hydrogen in the activity series i.e. Cu, Ag, Au cannot displace hydrogen from dilute acids, because they are less reactive than hydrogen.
8. In the electrolytic refining of M, what would you take as the anode, the cathode and the electrolyte?
Ans. For electrolytic refining of M:
Impure metal M → will be an anode
A pure sample of M → will be a cathode
Electrolyte → Acidified, a soluble salt of metal M
9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it as shown in the figure below:
(a) What will be the action of gas on
(i) dry litmus paper? (ii) moist litmus paper?
(b) Write the balanced chemical equation for the reaction taking place.
Ans. (a) (i) There will be no effect of gas on dry litmus paper.
(ii) Moist blue litmus paper turns red.
10. State two ways to prevent the rusting of iron.
Ans. (i) Rusting can be prevented by painting iron articles so that iron surface does not come in contact with air and moisture required for rusting.
(ii) By coating iron articles with a protective layer of zinc metal i.e. by galvanization which prevents the rusting of iron.
11. What type of oxides are formed when non-metals combine with oxygen?
Ans. When non-metals combine with the oxygen they form acidic oxides. E.g. SO2, CO2, NO2.
12. Give reasons:
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans. (a) Platinum, gold and silver are used to make jewellery because of their bright shiny surface and high resistance to corrosion. Also, they have high malleability and ductility for which they can be converted to any desired shape.
(b) Na, K and Li are highly reactive metals, they react with oxygen present in the air at room temperature and catches fire in presence moisture. hence Sodium, potassium and lithium are stored under oil to prevent their reaction with oxygen, moisture and carbon dioxide of air since They don’t react with oil (kerosene).
(c) Aluminium form a very protective layer of Aluminium oxide () on its surface which protects it from corrosion or reaction with any food item. It is also cheap, easily available, malleable and ductile. Therefore, it is used to make utensils for cooking.
(d) Reduction of metal oxides to metal is cheaper and easier than the reduction of carbonate and sulphide ores. So carbonate and sulphide ores are first converted into metal oxides by roasting and calcination, and then further reduced to form metals.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessel?
Ans. In tarnished copper vessel there is a layer formed due to corrosion which is basic in nature. when we rub the vessel with the lemon or tamarind juice, the acid present in it dissolves the copper carbonate. thus the vessel appears shiny.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Ans:- 1) Metals lose electrons to form positive ions.
Non-metals gain electrons to form negative -ions.
2)Oxides of metal are basic in nature.
Oxides of non-metals are acidic in nature.
3)Metals have ionic bonds.
Non-metals have covalent bonds.
4)Metals displace hydrogen from water.
Non-metals cannot do so.
15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument, the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Ans. The solution used by the goldsmith is aqua regia which is a mixture of conc. HCl acid and conc. HNO3 acid in 3:1 ratio. It is capable of dissolving metals like Gold. Since the outer layer of the gold, bangles is dissolved in aqua regia so their weight was reduced drastically.
16. Give a reason why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans. Copper does not react with cold water, hot water or steam.however steel (an alloy of iron) reacts with steam.if the hot water tanks are made of steel, then iron would react vigorously with the steam formed from hot water. that is why copper is used to make hot water tanks, not steel.