Page 213 - Chemistry ICSE Class X

Metallurgy 199
Ans. Some metals get affected by oxygen (in the air) and moisture even at room temperature. So, when such metals
are exposed to air for a long time they get corroded and give a dull appearance.
Q.4. 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 when exposed to moist air gets tarnished due to the formation of basic copper carbonate (CuCO .
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Cu(OH) ). Lemon or tamarind juice contains organic acids. These acids react with basic copper carbonate and
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clean the surface.
Q.5. Which of the following methods is suitable for preventing an iron frying pan from rusting? (a) applying oil (b)
applying paint (c) applying a coating of zinc (d) all of the above
Ans. The correct answer is (a).
The frying pan can be protected from corrosion by applying oil. (only certain special paints can be used which
can withstand high temperatures)
Zinc is a low melting metal. It gets vaporised. So, it is not advisable to use zinc for coating a frying pan.
Q.6. 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. The correct answer is (c).
Zinc is more reactive than tin. Moreover, tin is a nontoxic metal.
Q.7. Describe the corrosion of copper (or brass) when kept in a humid place.
Ans. On standing in moist air, copper/brass gets coated with a green coating of basic copper carbonate.
Q.8. Would it be right to store
(a) a solution of silver nitrate (AgNO ) in a copper vessel?
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(b) a solution of zinc sulphate (ZnSO ) in a lead vessel?
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Explain your answer.
Ans. (a) A solution of silver nitrate should not be placed in a copper vessel. This is because copper is more
electropositive than silver. As a result, copper (from the vessel) will slowly dissolve to cause holes in it, and
silver metal will get precipitated.
(b) Zinc sulphate solution can be stored in a lead vessel because lead is less electropositive than zinc. So, lead
will remain unaffected.

ASSIGNMENT 5
Uses of iron, zinc and aluminium, Corrosion, Rusting of iron and its prevention

ϭ͘ EĂŵĞ ƚŚĞ ƉŝŐŵĞŶƚƐ ďĂƐĞĚ ŽŶ njŝŶĐ͗ ;ĂͿ ǁŚŝƚĞ ŝŶ ĐŽůŽƵƌ ;ďͿ LJĞůůŽǁ ŝŶ ĐŽůŽƵƌ͘
Ϯ͘ DĞŶƟŽŶ ƚǁŽ ƵƐĞƐ ŽĨ njŝŶĐ͘
ϯ͘ ,Žǁ ĚŽ ƚŚĞ ĨŽůůŽǁŝŶŐ ĚŝīĞƌ ŝŶ ƚĞƌŵƐ ŽĨ ĐĂƌďŽŶ ĐŽŶƚĞŶƚ͍
;ĂͿ ĐĂƐƚ ŝƌŽŶ ;ďͿ ƐƚĞĞů ;ĐͿ ǁƌŽƵŐŚƚ ŝƌŽŶ
ϰ͘ tŚLJ ŝƐ njŝŶĐ ǁŚŝƚĞ ƉĂŝŶƚ ƐƵƉĞƌŝŽƌ ƚŽ ůĞĂĚ ǁŚŝƚĞ ƉĂŝŶƚ͍
ϱ͘ DĞŶƟŽŶ ƚŚƌĞĞ ƵƐĞƐ ŽĨ ĂůƵŵŝŶŝƵŵ͘ ůƐŽ ŵĞŶƟŽŶ ƚŚĞ ƉƌŽƉĞƌƟĞƐ ǁŚŝĐŚ ĨŽƌŵ ƚŚĞ ďĂƐŝƐ ŽĨ ƚŚĞƐĞ ƵƐĞƐ͘
ϲ͘ EĂŵĞ ƚǁŽ ĂůůŽLJƐ ŽĨ ĂůƵŵŝŶŝƵŵ ǁŚŝĐŚ ĂƌĞ ƵƐĞĚ ŝŶ ĂĞƌŽƉůĂŶĞ ĂŶĚ ĐĂƌ ŝŶĚƵƐƚƌLJ͘
ϳ͘ tŚĂƚ ŚĂƉƉĞŶƐ ǁŚĞŶ ŝƌŽŶ ŝƐ ŬĞƉƚ ĞdžƉŽƐĞĚ ƚŽ ŚƵŵŝĚ ĂƚŵŽƐƉŚĞƌĞ͍ džƉůĂŝŶ ƚŚĞ ƉƌŽĐĞƐƐ ďLJ ǁƌŝƟŶŐ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶƐ͘
ϴ͘ ĞĮŶĞ ƚŚĞ ƚĞƌŵ ŐĂůǀĂŶŝƐĂƟŽŶ͘
ϵ͘ tŚĂƚ ĂƌĞ ƚŚĞ ĞƐƐĞŶƟĂů ĐŽŶĚŝƟŽŶƐ ĨŽƌ ƌƵƐƟŶŐ ƚŽ ƚĂŬĞ ƉůĂĐĞ͍