Chapter 3 : Metals and Non-Metals

Internal Question and Answer:

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 : (i) Mercury is a liquid at room temperature.
(ii) Sodium (or Potassium) can be easily cut with a knife.
(iii) Silver (or Copper) is the best conductor of heat.
(iv) Lead (or Mercury) is a poor conductor of heat.
2. Explain the meanings of malleable and ductile.

Answer :  The property of metals by which they can be beaten into thin sheets is called malleability. For example : Gold and Silver .
The property of metals by which they can be drawn into thin wires is called ductility. For example : Gold .

Internal Question and Answer:

1. Why is sodium kept immersed in kerosene oil?
Answer:  Sodium is kept immersed in kerosene oil because it reacts so vigorously with air and moisture that it can catch fire if exposed. Immersing it in kerosene prevents accidental fires and protects the metal from reacting.

2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water.

Answer: (i) When iron react with steam then produce iron oxide and  hydrogen gas .

(ii) When calcium react with water then produce calcium hydroxide and hydrogen gas .

 When potassium with water then produce potassium hydroxide and hydrogen gas .

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.

Metal	Iron(II) sulphate	Copper(II) sulphate	Zinc sulphate	Silver nitrate
A	No  reaction	Displacement
B	Displacement		No  reaction
C	No  reaction	No  reaction	No  reaction	Displacement
D	No  reaction	No  reaction	No  reaction	No  reaction

Use the Table above to answer the following questions about metals A, B, C and D.
(a) Which is the most reactive metal?
(b) What would you observe if B is added to a solution of Copper(II) sulphate?
(c) Arrange the metals A, B, C and D in the order of decreasing reactivity.

Answer:  (a) B is the most reactive metal . (B metal more reactive than Iron)

(b) If B is added to a copper (II) sulphate solution, then B has displaced or removed another copper component from the copper sulphate (II) solution.

(c)  B>A>C>D .
4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute  .

Answer: When dilute hydrochloric acid is added to a reactive metal then produce salt and hydrogen gas .

 Metal + Dilute → Salt + Hydrogen gas .

When iron reacts with dilute  then produce iron(II) sulphate and hydrogen gas .

 
5. What would you observe when zinc is added to a solution of iron(II) sulphate ? Write the chemical reaction that takes place.

Answer: When zinc is added to a solution of iron(II) sulphate then produce zinc sulphate

Internal Question and Answer:

1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?

Answer:  (i) Electron-dot structures for sodium (Na), oxygen (O), and magnesium (Mg):

Sodium (Na) : Atomic number of Na is 11 .

Electronic configuration sodium (Na) is 2.8.1

              

Oxygen (O): Atomic number of O is 8 .

Electronic configuration oxygen (O) is 2.6

             

Magnesium (Mg): Atomic number of Mg is 12 .

Electronic configuration magnesium (Mg) is 2.8.2

                 

(ii) Formation of and MgO by the transfer of electrons:

  : Atomic number of Na is 11

Electronic configuration of Na is 2.8.1

Atomic number of O is 8

Electronic configuration of Na is 2.6

 

Formation of :

Sodium (Na) donates one electron to oxygen (O) to form and ions. The ionic compound is formed by the transfer of electrons.

MgO :

Atomic number of Mg is 12

Electronic Configuration of Mg is 2.8.2

 

Atomic number of O is 8

Electronic Configuration of Na is 2.6

  

Formation of MgO :

Magnesium (Mg) donates two electrons to oxygen (O) to form and ions. The ionic compound MgO is formed by the transfer of electrons.

(iii) Ions present in these compounds:

In  , the ions present are  (sodium ion) and  (oxide ion).

In , the ions present are   (magnesium ion) and  (oxide ion).
2. Why do ionic compounds have high melting points?

Answer: Ionic compounds have high melting points. This is because a considerable amount of energy is needed to break the strong inter-ionic attraction.

Internal Question and Answer:

1. Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue

Answer: (i) Mineral : Elements or compounds naturally present on the Earth's crust are called minerals.

(ii) Ore : In certain places, minerals contain a very high percentage of a particular metal and the metal can be extracted profitably. These minerals are called ores.

(iii) Gangue : Minerals extracted from the ground are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
2. Name two metals which are found in nature in the free state.

Answer:  Gold and silver .
3. What chemical process is used for obtaining a metal from its oxide?

Answer: The chemical process used for obtaining a metal from its oxide is called reduction.

Internal Question and Answer :

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

Metal	Zinc	Magnesium	Copper
Zinc oxide	------	Displacement reaction	------
Magnesium oxide	-----	------	-------
Copper oxide	Displacement reaction	Displacement reaction	-----

In which cases will you find displacement reactions taking place?

Answer : A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its oxide.

Zinc + Copper oxide → Zinc oxide + Copper (Displacement reaction)

Magnesium + Zinc oxide → Magnesium oxide + Zinc (Displacement reaction)

Magnesium + Copper oxide → Magnesium oxide + Copper (Displacement reaction)

2. Which metals do not corrode easily?

Answer: Some metals are found in the earth’s crust in the free state . This type of metal can not be  easily corroded. For example:  gold, silver, platinum and copper .

3. What are alloys?
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Exercises of Chapter 3 : Metals and Non-Metals :

1. Which of the following pairs will give displacement reactions?
(a)  solution and copper metal
(b)  solution and aluminium metal
(c)  solution and silver metal
(d)  solution and copper metal.
Answer: (d)  solution and copper metal.
[ Copper is more reactive than silver, so it displaces silver from silver nitrate solution: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag ]

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: (c) Applying a coating of zinc

[ Coating iron with zinc (galvanisation) prevents it from coming in contact with air and moisture, thus protecting it from rusting. Methods like grease or paint are not suitable for a frying pan because they would burn or wear off during cooking.]
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:  (a) Calcium .

[ Calcium reacts with oxygen to form calcium oxide (CaO), which has a high melting point. It also reacts with water to form calcium hydroxide, which is soluble in water. Hence, the element is calcium.]
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: (c) zinc is more reactive than tin.

[ Zinc is more reactive and can react with food, which may make it unsafe. Tin is less reactive and does not easily react with food substances, so it is used for coating food cans.]

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 :  (a) With the help of a hammer, the sample can be tested for malleability. If the substance can be beaten into thin sheets without breaking, it is a metal. If it breaks or turns into powder, it is a non-metal. Using the battery, bulb, wires and switch, a simple electric circuit can be made. The sample is placed in the circuit; if the bulb glows, the substance conducts electricity and is a metal. If the bulb does not glow, it is a non-metal.

(b) These tests are useful in most cases because metals are generally malleable and good conductors of electricity, while non-metals are usually brittle and poor conductors. However, these tests are not completely reliable because there are exceptions. For example, some metals like sodium are soft and cannot be tested with a hammer, and some non-metals like graphite conduct electricity. Hence, these properties give a general idea but are not always sufficient to clearly distinguish between metals and non-metals.

6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer: The metal oxides which react with both acids as well as bases to produce salts and water are called amphoteric oxides.  Example:  and (Sodium aluminate) .

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer: Magnesium and Aluminium are two metals which will displace hydrogen from dilute acids.

Copper and gold are two metals which will not displace hydrogen from dilute acids.

8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Answer: In the electrolytic refining of a metal M, the impure metal M is taken as the anode, a thin strip of pure metal M is taken as the cathode, and a solution of a salt of the same metal M is used as the electrolyte.

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: (a) When sulphur is heated, it forms sulphur dioxide gas.
(i) On dry litmus paper, there is no change in colour.
(ii) On moist litmus paper, the gas turns blue litmus red because it forms an acidic solution.

(b) The balanced chemical equation is: S + O₂ → SO₂ 

10. State two ways to prevent the rusting of iron.
Answer:  There are two ways to prevent the rusting of iron :

(i) Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.

(ii) Alloying is a very good method of improving the properties of a metal.

11. What type of oxides are formed when non-metals combine with oxygen?
Answer: When non-metals combine with oxygen, they generally form acidic oxides. These oxides dissolve in water to form acids.

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: (a) Platinum, gold and silver are used to make jewellery. It is because of their malleability and ductility that metals can take various forms depending on our needs .

(b) Because sodium, potassium and lithium are most reactive metals so that these kinds of metals react vigorously that they catch fire if held in the open air. Therefore, to protect them from accidental fires, they are kept the oil .

(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking . Because metals are good heat conductors with high melting points.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction. Because it is easier to get a metal from its oxide instead of its sulphides and carbonates.

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: Copper vessels get tarnished due to the formation of a green layer of basic copper carbonate on their surface. Lemon and tamarind contain acids such as citric acid and tartaric acid. These acids react with the basic copper carbonate and dissolve it, forming soluble substances which can be washed away.Hence, sour substances are effective in cleaning copper vessels.

14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer: The difference between metals and non-metals based on their chemical properties :

Basis of Difference	Metals	Non-metals
Reaction with oxygen	Metals react with oxygen to form basic oxides.	Non-metals react with oxygen to form acidic or neutral oxides.
Reaction with water	Many metals react with water to produce hydrogen gas and metal hydroxides.	Non-metals generally do not react with water.
Reaction with acids	Metals react with dilute acids to form salt and hydrogen gas.	Non-metals generally do not react with dilute acids.
Electron transfer	Metals lose electrons to form positive ions (cations).	Non-metals gain electrons to form negative ions (anions).
Type of compounds formed	Metals usually form ionic compounds.	Non-metals usually form covalent compounds.

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: The goldsmith had used aqua regia, which is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. It dissolves a small amount of gold from the surface of the bangles, making them shiny but reducing their weight.

16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Answer: Copper is used to make hot water tanks because it is less reactive and does not react with hot water or steam. This means it does not corrode easily and remains safe for long-term use.