Maharashtra Board Class 8 Science Solution Chapter 7 – Metals and Nonmetals
Balbharati Maharashtra Board Class 8 Science Solution Chapter 7: Metals and Nonmetals. Marathi or English Medium Students of Class 8 get here Metals and Nonmetals full Exercise Solution.
|Maharashtra Class 8|
General Science Solution
Metals and Nonmetals
(i) Ductility – Bridge.
(ii) Malleability – Metal Container use in homes in kitchen.
(iii) Conduction of heat – cooking electric press.
(iv) Conduction of electricity – electrical wire.
(v) Sonority – Doorbells.
(2) Identify the odd term
(a.) Gold, silver, iron, diamond
(b.) Ductility, brittelness, sonority, malleability
(c.) Carbon, bromine, sulphur, phosphorus
(d.) Brass, bronze, iron, steel
(3) Write scientific reasons.
(a.) The stainless steel vessels in kitchen have copper coating on the bottom.
(b.) Copper and brass vessels are cleaned with lemon.
(c.) Sodium metal is kept in kerosene.
(3) (a) The stainless vessels in kitchen have copper coating on the bottom:- Copper coating help in faster heat conduction & more even heating of the vessel. Stainless steel does not faster heat very. So copper helps spread the heat.
(b) Copper & brass vessels are cleaned with lemon:-
Lemon juice have citric acid which etches away copper oxide that gives the vessels the dark colour.
(c) Sodium Metal is kept in Kerosene:-
Sodium metal is very reactive. When exposed to air, it react with oxygen, moisture & carbon di oxide present in the air.
4Na + O2 = 2Na2O
2Na2O + 2H2O = 4NaOH
4NaOH + 2CO2 = 2Na2CO3 + 2H2O
Therefore, to prevent these reactions & protect the metal, sodium is kept under Kerosene.
(4.) Answer the following.
(a.) What is done to prevent corrosion of metals?
(b.) What are the metals that make the alloys brass and bronze?
(c.) What are the adverse effects of corrosion?
(d.) What are uses of Noble metals?
(4) (a) Prevent corrosion of metal:-
(i) Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting.
(ii) Cathodic protection is the process used to control the corrosion of metal surface.
(iii) Electro galvanigation is a another process in which a layer of zinc is bonded to steel in order to protect against corrosion.
(b) The metals that makes the alloys brass & bronze:-
Brass is an alloy of copper & zinc.
Bronz is an alloy of Copper & Tin.
(c) The adverse effect of corrosion:-
(i) Due to destructive attack corrosion is the degradation of metals, which is called rust.
(ii) Reduction in efficiency of metal.
(iii) Excessive overdesign.
(iv) Plant shutdown.
(d) Use of Nobel Metal:-
Nobel metal do not react with the environment or any other. They are silver, gold, platinum, rhodium, palladium, ruthenium.
i) Used in dental costing.
ii) Used in Jewellaery, dentistry, blood sugar testing strips.
iii) Improving resistance to corrosion.
(5) Three experiments to study the process of rusting are given below. Observe the three test tubes and answer the following questions.
(a.) Why the nail in the test tube 2 is not rusted ?
(b.) Why is the nail in the test tube 1 is rusted highly?
(c.) Would the nail in the test tube 3 get rusted ?
(5) (a) The nail is placed in boiled water & oil which prevents rusting.
Water is major factor that causes the oxidation procedure. Without water, oxygen can’t stat the oxidation. Other side oil & water don’t blend. So the nail does not rusted.
(b) The nail is placed in open space and when it comes in contact with water, it leads to the spontaneous oxidation process. So the nail highly rusted.
(c) Due to absence of air rusting is not terrible. The chemical such as Calcium Chloride dries out the air, So the nail will not get rusted.