Text Question
1. Give an example of a metal which
(i) Is a liquid at room temperature.
Ans: Mercury
(ii) Can be easily cut with a knife.
Ans: Sodium
(iii) Is the best conductor of heat.
Ans: Silver
(iv) Is a poor conductor of heat.
Ans: Mercury and lead
2. Explain the meaning of malleable and ductile.
Ans: Malleable: Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals and ductile.
Page no. 46
1. Why is sodium kept immersed in kerosene oil?
Ans: Sodium is high reactive element. If it is kept in open it can explosively react with oxygen to catch fire. Hence to prevent accidental damage sodium is immersed in kerosene oil.
2. Write equations for the reactions of
(i) Iron and steam
(ii) Calcium and potassium with water
Ans:
3. 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: Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal.
When iron reacts with dilute H2SO4 iron (ii) Sulphate with the evolution of hydrogen gas is formed
4. What would you observe when zinc is added to a solution of iron (ii) sulphate? Write the chemical reaction that takes place.
Ans: When zinc is added to iron (ii) sulphate then it will displace the iron from iron sulphate solution as shown in the following chemical reaction.
Page no. 49
1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na20 and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
Ans: The representation of elements with valence is referred to as electron-dot structure for elements.
2. Why do ionic compounds have high melting points?
Ans: Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.
Page no. 53
1. Define the following terms
(i) Mineral (ii) Ore (iii) Gangue
Ans: (i) Mineral: The naturally occuring compounds of elements are known as mineral.
(ii) Ore : Minerals from which metals can be extracted profitably are known as ores.
(iii) Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.
2. Name two metals which are found in nature in the free state.
Ans: The metals at the bottom of the reactivity series are mostly found in free state. For example: Gold, silver and platinum.
3. What chemical process is used for obtaining a metal from its oxide?
Ans: A metal can be extracted from its oxide by the process of reduction.
2HgO (s) + Heat ——> 2Hg (l) + O2
4. Which metals do not corrode easily?
Ans: Metals which have low reactivity such as silver, gold does not corrode easily.
5. What are alloys?
Ans: An alloy is the homogeneous mixture of two or more metals or metals and non metals. For example brass is an alloy of copper and zinc
Exercise
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.
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. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron.
Ans: (b) carbon
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.
Ans: (c) zinc is more reactive than tin.
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.
Ans: (a) With the hammer, we can beat the sample and if it can be beaten into thin sheets 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.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans: Those oxides that behave as both acidic and basic oxides are called amphoteric oxide.
Example: Aluminium oxide And Zinc oxide
7. Name two metals which will displace hydrogen from dilute acids, and two metal which will not.
Ans: Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Ans: 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
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?
Ans:
(b) Write a balanced chemical equation for the reaction taking place.
Ans: (a) (i) There will be no reaction on dry litmus paper.
(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.
(b) S(s) + O2(g) ——> SO2 (g)
10. State two ways to prevent the rusting of iron.
Ans: Two ways to prevent the rusting of iron are:
-
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.
-
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.
11. What type of oxides are formed when non-metals combine with oxygen?
Ans: When non-metals are combined with oxygen then neutral or acidic oxides are formed. Examples of acidic oxides are formed. Examples of acidic oxides are NO2, SO2 and examples of neutral oxides are NO,CO etc.
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.
Ans:
(a) Plantinum, 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 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 futher 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.
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.
Ans: Copper reacts with moist carbon dioxide in air to from copper carbonate and as a result, copper vessels loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tarmarind neutralises the bases copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tarmarind juice to give the surface of the copper vessel its characteristic lusture.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Ans:
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?