Answer The Following Question.
1. 1. Give an example of metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with knife.
(iii) is best conductor of heat.
(iv) is poor conductor of heat.
Solution :
(i) Mercury
(ii) Sodium
(iii) Silver
(iv) Lead
2. Explain the meaning of malleable and ductile.
Malleable:
A substance is said to be malleable if it can be beaten into thin sheets.
Examples: Iron, Copper.
Ductile:
A substance is said to be ductile if it can be drawn into thin wires.
Examples: Gold, Silver.
3. Why is sodium kept immersed in kerosene oil?
Ans:
Sodium is highly reactive and reacts vigorously with oxygen, often catching fire when exposed to air. To prevent accidental fires and ensure safety, sodium is kept immersed in kerosene oil, which acts as a protective layer to isolate it from air and moisture.
4. Write equation for the reaction of
(i) Iron with steam
(ii) Calcium and potassium with water
5. 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 given above to answer the f0llowing 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 order of decreasing reactivity.
Solution :
(i) B is the most reactive metal
(ii)If B is added to a solution of copper (II) sulphate, displacement reaction will take place. Blue colour of copper sulphate will fade and red –brown copper will settle down.
(iii) The decreasing order of reactivity is:
B> A> C >D
6. Which gas is produced when dilute hydrochloric acid is added to reactive metal?
Hydrogen gas is produced when dilute hydrochloric acid reacts with a reactive metal. For example, when iron reacts with dilute HCl, iron (II) chloride and hydrogen gas are formed.
Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)
7.What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Solution : As zinc is more reactive than iron, displacement reaction will take place
Fe SO4(aq) + Zn(s) → ZnSO4(aq) + Fe(s)
8. (i)Write the electro-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?
iii) Ions present in Na2O are Na+ and O2-
Ions present in MgO are Mg2+ and O2-
9.Why do ionic compounds have high melting points?
Ionic compounds have high melting points because of the strong electrostatic forces of attraction between oppositely charged ions. A considerable amount of energy is required to overcome these strong inter-ionic forces, leading to high melting points.
10. Define the following terms :
(i) Minerals
(ii) Ores and
(iii) Gangue
Ans :
(i) Minerals- the element or compounds which occur naturally in the earth crest are known as minerals.
(ii) Ores- Minerals from which metal can be extracted profitably and easily are called ores.
(iii) Gangue- Impurities such as soil and sand which are present in the minerals are called gangue.
11.Name two metals which are found in nature in the free state.
Solution : Gold and Platinum
12. What chemical process is used for obtaining a metal from its oxide?
Solution : A metal is obtained from its oxide by the process of reduction.
13. Metallic oxide of zinc, magnesium and copper were heated with following metals
In which case will you find displacement reactions tking place?
Ans : Based on the activity series of metals, the displacement reactions will take place as below:
14. Which metals do not corrode easily?
Metals like silver, gold, and platinum, which are placed at the bottom of the reactivity series, do not corrode easily because they are least reactive and resist oxidation and environmental effects.
15. What are alloys?
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. It is made by first melting the primary metal and then mixing the other element(s) in definite proportions.
For example:
Brass (Copper + Zinc)
Steel (Iron + Carbon).
16. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminum
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper
Ans : (d) AgNO3 solution and copper
17. Which of the following method is suitable for preventing an iron fry pan from rusting?
(a) Applying grease
(b) applying paint
(c) Applying coating of zinc
(d) All of the above
Solution : (c) Applying coating of zinc
18. 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
Ans : (a) Calcium
19. Food cans are coated with tin and not zinc because
(a) Zinc is costlier than tin
(b) Zinc has higher melting point
(c) Zinc is more reactive than tin
(d) Zinc is less reactive than tin
Solution : (c) Zinc is more reactive than tin
20. 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 metals and non-metals:
Malleability Test:Place the sample on an iron block and strike it with a hammer.
If the sample flattens into a sheet, it is a metal.
If it shatters into pieces, it is a non-metal.
Conductivity Test:Set up an electric circuit using a bulb, battery, wires, and switch.
Insert the sample into the circuit.
If the bulb glows, the sample is a metal (good conductor).
If the bulb does not glow, the sample is a non-metal (poor conductor).
(b) These tests are generally effective in distinguishing between metals and non-metals, as metals are malleable and good conductors of electricity, whereas non-metals are brittle and poor conductors.
21. What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans:
Amphoteric oxides are metal oxides that exhibit both acidic and basic properties. They can react with both acids and bases to form salt and water.
Examples:
Aluminum oxide (Al₂O₃)
Zinc oxide (ZnO)
22. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Ans:
Metals that will displace hydrogen from dilute acids:
Magnesium (Mg)
Zinc (Zn)
Metals that will not displace hydrogen from dilute acids:
Copper (Cu)
Silver (Ag)
23. 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 strips of pure metal M
Electrolyte: Salt solution of metal M (e.g., metal M chloride or sulfate solution)
In this process, the impure metal M dissolves from the anode and deposits as pure metal M on the cathode.
23. 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 strips of pure metal M
Electrolyte: Salt solution of metal M (e.g., metal M chloride or sulfate solution)
In this process, the impure metal M dissolves from the anode and deposits as pure metal M on the cathode.
24. Pratyush took Sulpher powder on spatula and heated it. He collected the gas evolved by inverting a test tube over it as shown in fig. 3.12 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.
Ans:
When sulfur powder is heated, sulfur dioxide (SO₂) gas is evolved.
(a) Action of gas on litmus paper:
(i) Dry litmus paper: The dry litmus paper will remain unaffected by sulfur dioxide, as the gas does not interact with dry litmus paper.
(ii) Moist litmus paper: The sulfur dioxide gas dissolves in the moisture on the litmus paper and forms sulfurous acid (H₂SO₃), which is acidic. As a result, the moist litmus paper will turn red, indicating the acidic nature of the gas.
(b) Balanced chemical equation: The reaction that takes place when sulfur is heated and combines with oxygen is as follows:
25. State two ways to prevent the rusting of iron.
Ans:
Two ways to prevent the rusting of iron are:
Applying grease or paint: Coating the iron surface with grease or paint creates a protective layer that prevents contact with oxygen and moisture, which are necessary for rust formation.
Galvanizing: Galvanizing involves coating iron with a layer of zinc. Zinc acts as a protective barrier and also prevents rusting by sacrificing itself (acting as a sacrificial anode) when exposed to moisture.
26. What types of oxides are formed when non-metals combine with oxygen?
Ans:
When non-metals combine with oxygen, they form acidic oxides. These oxides tend to dissolve in water to form acidic solutions. For example, when sulfur reacts with oxygen, it forms sulfur dioxide (SO₂), which, when dissolved in water, forms sulfurous acid (H₂SO₃).
27. Give reasons :
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminum is highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphides ores are usually converted into oxides during the process of extraction.
Ans:
(a) Platinum, gold, and silver are used to make jewellery because they are unreactive and do not tarnish or corrode easily. These metals maintain their shine and appearance over time.
(b) Sodium, potassium, and lithium are stored under oil because they react violently with oxygen and moisture in the air. To prevent them from catching fire and reacting, they are kept submerged in kerosene or oil.
(c) Aluminum is highly reactive, but it is used to make utensils for cooking because it is a good conductor of heat. At high temperatures, aluminum forms a thin protective layer of aluminum oxide, which prevents further corrosion and protects it from reacting with food or water.
(d) Carbonate and sulphide ores are usually converted into oxides during the extraction process because it is easier to reduce metal oxides to metals than to reduce carbonates or sulphides directly. Oxides are more stable and more readily reduced in the extraction of metals.
28. 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.
Copper vessels tarnish due to the formation of copper carbonate. Lemon or tamarind juice, which contain acids, react with copper carbonate to form soluble copper salts, effectively cleaning the vessels.
29. Differentiate between metal and non-metal on the basis of their chemical properties.
Here is the comparison between metals and non-metals based on their chemical properties:
Reaction with Oxygen:
Metals form basic oxides (e.g., Na₂O).
Non-metals form acidic or neutral oxides (e.g., CO₂).
Reaction with Water:
Metals like sodium react vigorously with water to form hydroxides and hydrogen gas (e.g., Na + H₂O → NaOH + H₂).
Non-metals generally do not react with water.
Reaction with Acids:
Metals react with acids to produce salt and hydrogen gas (e.g., Zn + HCl → ZnCl₂ + H₂).
Non-metals do not react with acids in the same way.
Formation of Ions:
Metals lose electrons to form positive ions (cations), e.g., Na → Na⁺.
Non-metals gain or share electrons to form negative ions (anions), e.g., Cl + e⁻ → Cl⁻.
Conductivity:
Metals are good conductors of electricity and heat.
Non-metals are poor conductors of electricity and heat (except graphite, which is a good conductor).
State at Room Temperature:
Most metals are solid at room temperature (except mercury, which is liquid).
Non-metals exist in all three states: solids (e.g., sulfur), liquids (e.g., bromine), and gases (e.g., oxygen).
30. A man went door to door posing as a goldsmith. He promised to bring back the glitter of the old and dull 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 man was likely aqua regia, a highly corrosive mixture of three parts concentrated hydrochloric acid (HCl) and one part concentrated nitric acid (HNO₃). Aqua regia is known for its ability to dissolve gold, which is otherwise quite resistant to most acids.
When the man dipped the gold bangles in aqua regia, the outer layer of the gold dissolved, causing the bangles to shine. However, because the gold was lost from the surface, the weight of the bangles was reduced drastically. This explains why the bangles appeared to sparkle but their weight decreased, leading to the lady’s upset.
31. Give reasons, why copper is used to make hot water tanks and not steel (an alloy of iron).
Copper is used to make hot water tanks instead of steel because copper has high thermal conductivity, which allows it to transfer heat efficiently. This property makes copper an ideal material for quickly heating water. On the other hand, steel (an alloy of iron) has lower thermal conductivity compared to pure copper, making it less efficient in transferring heat. Therefore, copper is preferred for applications like hot water tanks, where heat transfer is crucial.