1.Explain the following terms with reference to the physical properties of metals.
a) Metallic lustre
b) Hardness
c) Malleability
d) Ductility
e) Thermal conductivity
f) Electrical conductivity
g) Sonority
(Chapter 3 : Metals and Non-metals)
Ans :
a) Metallic lustre: Metals, in their pure state, have a shining surface. This property is
called metallic lustre.
b) Hardness: Metals are generally hard but the hardness among metal to metal varies.
c) Malleability: Some metals can be beaten into thin sheets. This property is called malleability.
d) Ductility : The ability of metals to be drawn into thin wires is called ductility.Gold is the most ductile metal. It is possible to generate a wire
of about 2 km length from one gram of gold.
e) Thermal conductivity : metals are good conductors of heat and have high melting points. The best conductors of heat are silver, copper and aluminium. So because of this property vessels of copper and aluminium are good in cooking. Lead is a poor conductor of heat.
f) Electrical conductivity : metals are good conductors of electricity. For example metals like copper, aluminium , silver are good conductors of electricity.
g) Sonority :The metals that produce a sound on striking a hard surface
are said to be sonorous.You will such metal used for ringing bells.
2. Name a non-metal that is liquid in nature.
(Chapter 3 : Metals and Non-metals)
Ans : Bromine
3. Name the different forms of carbon.
(Chapter 3 : Metals and Non-metals)
Ans :
Carbon is a non-metal that can exist in different forms and each form is called an allotrope.
Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point.
Graphite, another allotrope of carbon, is a conductor of electricity.
4. Explain amphoteric oxides.
(Chapter 3 : Metals and Non-metals)
Ans :
All metals combine with oxygen to form metal oxides.Some metal oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as well as basic behaviour. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.
5.The metal sodium is kept immersed in Kerosene oil in the school laboratory. Why is it not kept in the open ?
OR
Why is sodium kept immersed in kerosene oil?
(Chapter 3 : Metals and Non-metals)
Ans :
The metal sodium reacts vigorously and catches fire if kept in the open. To protect the metal and to prevent accidental fires, it is kept immersed in kerosene oil.
6.Why is the reaction of iron oxide with aluminum used in joining the railway tracks ?
(Chapter 3 : Metals and Non-metals)
Ans :
The reaction of iron oxide with aluminium ((Fe2O3)) is used to join railway tracks because it is a highly exothermic reaction.The amount of heat evolved is so large that the metals are obtained in the molten state which can be used to join railway tracks quickly.
7.Give an example of amphoteric oxides.
(Chapter 3 : Metals and Non-metals)
Ans :
Aluminium oxide reacts in the following manner with acids and bases -
Al2O3 + 6HCl ---> 2AlCl3 + 3H2O
Al2O3 + 2NaOH ---> 2NaAlO2 + H2O
(Sodium Aluminate)
8.Why is the surface of metals like magnesium, aluminium, zinc, lead, covered with a thin layer of oxide?
(Chapter 3 : Metals and Non-metals)
Ans : The protective oxide layer prevents the metal from further oxidation.
9.What is anodising?
(Chapter 3 : Metals and Non-metals)
Ans : Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made at the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.
10.What happens when Metals react with Water?
(Chapter 3 : Metals and Non-metals)
Ans :
Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide.
Metal + Water → Metal oxide + Hydrogen
Metal oxide + Water → Metal hydroxide
11.What is Aqua regia ?
(Chapter 3 : Metals and Non-metals)
Ans : Aqua regia, (Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.
12.Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
(Chapter 3 : Metals and Non-metals)
Ans :
Hydrogen gas is produced when dilute HCl is added to reactive metal.
Chemical Equation when iron reacts with dilute H2SO4:
Fe(s) + H2SO4(aq) ---> FeSO4(aq) + H2(g)
13.What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
(Chapter 3 : Metals and Non-metals)
Ans :
When zinc is added to the solution of iron(II) sulphate the color of the solution(iron sulphate) changes from green to colourless.
This happens because the zinc displaces iron to form zinc sulphate and iron metal. The grey precipitate of iron metal is deposited at the bottom and the zinc sulphate solution becomes colorless.
Chemical Equation:
Zn + FeSO4 ---> ZnSO4 + Fe