Page 40
Question 1. Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Answer 1
(i) Metal that exists in liquid state at room temperature → Mercury.
(ii) Metal that can be easily cut with a knife → Sodium, Potassium.
(iii) Metal that is the best conductor of heat → Silver, Gold.
(iv) Metals that are poor conductors of heat → Mercury and lead.
Question 2. Explain the meanings of malleable and ductile.
Answer 2 Malleable: Substances that can be beaten into thin sheets are called malleable. Most of the metals are malleable. Gold and Silver are the most malleable metals.
Ductile: Substances that can be drawn into thin wires are called ductile. Most of the metals are ductile. Gold is the most ductile metal.
Page 46
Question 1. Why is sodium kept immersed in kerosene oil?
Answer 1) Sodium is kept immersed in kerosene oil because potassium and sodium react so vigorously that they catch fire if kept in the open. Thus, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
Question 2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Answer 2:
(i) Iron react with steam to form the metal oxide and hydrogen.
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(ii) The reaction of calcium with water is exothermic but the heat evolved is not sufficient for the hydrogen to catch fire.
Ca(s) + 2 H2O(l) ——> Ca(OH)2 (aq) + H2 (g)
Question 3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.
Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of Copper(II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer 3 :
(i) As per reactivity series, Iron is most reactive metal among Iron, Silver and Copper. Since B can displace Iron from its sulphate, so B is the most reactive metal.
(ii) As B is more reactive than Iron, so it will displace Copper from its Copper Sulphate solution.
(iii) B is most reactive and D is the least reactive metal as unable to displace any of the solutions. Copper is more reactive than Silver and metal A can displace Copper, so A is more reactive than C.
Hence, the order of decreasing reactivity is B > A > C > D.
Question 4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Answer 4 When reactive metals react with dilute hydrochloric acids, gives a salt and hydrogen gas.
Metal + Dilute acid → Salt + Hydrogen
Reaction between Iron and H2SO4:
Fe + H2SO4 → FeSO4 + H2
Question 5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer 5 Zinc is more reactive than Iron. When Zinc is added to Iron (II) Sulphate solution, Zinc displaces iron from its solutions and Zinc sulphate is formed.
Zn(s) + FeSO4(aq) → ZnSO4(aq) + Fe(s)
Page 49
Question 1. (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?
(i) (a) Electron – dot structure for Sodium:
(b) Electron – dot structure for Oxygen:
(c) Electron – dot structure for Magnesium:
(ii) Formation of Na2O by transfer of electron:
Formation of MgO by transfer of electron:
(iii) Ions present in these compounds are Mg2+ , O2-, Na+
Question 2. Why do ionic compounds have high melting points?
Answer 2 Ionic compounds have high melting and boiling points because they are formed by the attraction force of two opposite ions and a considerable amount of energy is required to break this strong inter-ionic attraction.
Page 53
Question 1. Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
Answer 1
(i) Mineral: The elements or compounds which occur naturally in the earth’s crust are known as minerals.
(ii) Ore: If minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.
(iii) Gangue: Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
Question 2. Name two metals which are found in nature in the free state.
Answer 2 Gold, silver, platinum and copper are found in the free state.
Question 3. What chemical process is used for obtaining a metal from its oxide?
Answer 3 (i) Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone.
2HgO(s) Heat → 2Hg(l) + O(g)
(ii) The metals in the middle of the activity series such as iron, zinc, lead, copper, etc., are moderately reactive. These metal oxides are reduced to the corresponding metals by using suitable reducing agents.
ZnO(s) + C(s) → Zn(s) + CO(g)
(iii) The metals high up in the reactivity series are very reactive. They are separated from their oxides by electrolysis process.
Page 55
Question 1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | |||
| Magnesium oxide | |||
| Copper oxide |
In which cases will you find displacement reactions taking place?
Answer 1 Magnesium is the most reactive among these three metals and Zinc is more reactive than Copper. So, Magnesium will displace Zinc oxide and Copper oxide whereas Zinc will displace Copper oxide only.
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | No reaction | Displacement Reaction | No reaction |
| Magnesium oxide | No reaction | No reaction | No reaction |
| Copper oxide | Displacement Reaction | Displacement Reaction | No reaction |
Question 2. Which metals do not corrode easily?
Answer 2 The metals which are less reactive, do not corrode easily.
For example: Gold, silver, platinum and copper.
Question 3. What are alloys?
Answer 3 An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
For example:
(i) Stainless steel is an alloy of Nickel and Chromium.
(ii) Amalgam is an alloy of Mercury.
(iii) Brass is an alloy of Copper and Zinc.
(iv) Bronze is an alloy of Copper and Tin.
(v) Solder is an alloy of Lead and Tin.
Page 56-57
Question 1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal.
Answer 1: (d) AgNO3 solution and copper metal.
Copper is above silver in the reactivity series of metals means it is more reactive than silver. If you were to place pure copper metal in a solution of silver nitrate, the copper ions will displace the silver ions out of solution.
Question 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.
Answer 2: (c) Applying a coating of zinc
Applying of grease or paint is not suitable for utensils used for cooking. Applying of zinc is a suitable method for preventing an iron frying pan from rusting because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.
Question 3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron.
Answer 3: (a) calcium
When carbon reacts with oxygen it forms carbon dioxide which is a gas. Gases do not possess melting point. Silicon reacts with oxygen and forms silicon dioxide. This is insoluble in water. Iron reacts with oxygen and forms Iron dioxide. This is insoluble in water. Calcium reacts with oxygen and forms calcium oxide. This calcium oxide dissolves in water and forms calcium hydroxide. The melting point of calcium oxide is nearly 2,500°C.
Question 4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
Answer 4: (c) zinc is more reactive than tin.
Food cans are coated with tin and not with zinc because zinc is more reactive than tin.
Question 5. You are given a hammer, a battery, a bulb, wires and a 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.
Answer 5:
(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets, means it is malleable, then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
Question 6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer 6 Amphoteric oxides are the oxides that behave as both acidic and basic oxides.
Examples: Aluminium oxide (Al2O3)
Al2O3 + 6HCl → 2AlCl3 + 3H2O [Basic]
Al2O3 + 2NaOH → 2NaAlO2 + H2O [Acidic]
Zinc oxide (ZnO) is also an amphoteric oxide.
ZnO (s) + 2 HCl (aq) ——-> ZnCl2 (aq) + H2O (l)
ZnO (s) + 2 NaOH (aq) ——-> Na2ZnO2 (aq) + H2O (l)
Question 7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer 7 Metals that are more reactive than hydrogen displace it from dilute acids.
For example: Sodium and potassium.
Metals that are less reactive than hydrogen do not displace it.
For example: Copper and silver.
Question 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer 8 In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M.
Electrolyte → Solution of salt of the metal M.
Question 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 figure below.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
Answer 9 (a) Action of gas on
(i) Dry litmus paper do not turn red or blue with acid or base. So, there is no effect on dry litmus paper.
(ii) Gas evolved is sulphur dioxide and is a non-metallic oxide and non-metallic oxides are acidic in nature.
Therefore, moist blue litmus paper turns red.
(b) When sulphur is burnt or heated in air, it gives sulphur dioxide gas.
S(s)+O2 (g) → SO2 (g)
SO2 (g)+H2O (l) → H2SO3 (aq)
Question 10. State two ways to prevent the rusting of iron.
Answer 10
Two ways to prevent the rusting of iron are:
(i) Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
(ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
Question 11. What type of oxides are formed when non-metals combine with oxygen?
Answer 11 Non-metals combine with oxygen to form acidic oxides.
For example: S(s)+O2 (g) → SO2 (g)
Question 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 a 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.
Answer 12:
(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.
Question 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 vessels.
Answer 13 : Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basic copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.
Question 14. Differentiate between metal and non-metal on the basis of their chemical properties.
| Metals | Non Metals |
| Metals are electropositive. | Non- metals are electronegative. |
| They react with oxygen to from basic oxides.
4Na+O2 → 2Na2O |
They react with oxygen to from acidic or neutral oxide.
C + O2 + →CO2 |
| These have ionic bonds. | These have covalent bonds. |
| They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water and some with steam.
2Na + 2H2O → 2NaOH +H2 ↑ |
They do not react with water. |
| They react with dilute acid form a salt and evolve hydrogen gas.
2Na+ 2HCl → 2NaCl +H2 ↑ |
They do not react with dilute acid. These are not capable of replacing hydrogen. |
| They react with the salt solution of metal. Depending on their reactivity, displacement reaction can occur.
CuSO4 + Zn—> ZnSO4 + Cu |
These react with the salt solutions of non metals. |
| They acts as reducing agents (as they can easily loose electrons) Na → Na+ + e – |
These acts as oxidising agents (as they can gain electrons). l2 + 2e– → 2 Cl– |
Question 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?
Answer 15 : Goldsmith must have dipped the gold metal in the solution of aqua regia − a 3: 1 mixture of concentrated HCl and concentrated HNO3. Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. Thus, the weight of gold ornament reduced.
Question 16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer 16 Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water.
3Fe + 4H2O → Fe3O4 + 4H2
That is why copper is used to make hot water tanks, and not steel.
Very helpful.