Page 208 - Chemistry ICSE Class X

194 ICSE Chemistry – 10
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2Al + 3S o Al S
^ŽŵĞ ŵĞƚĂůƐ ǁĞƌĞ ŬŶŽǁŶ ƚŽ ƚŚĞ 2 3
ĂŶĐŝĞŶƚ ƉĞŽƉůĞ͘ dŚĞƐĞ ŵĞƚĂůƐ ǁĞƌĞ aluminium aluminium sulphide
ƵƐĞĚ ďLJ ƚŚĞŵ ŝŶ ŵĂŶLJ ĚŝīĞƌĞŶƚ ǁĂLJƐ͘ ƒ Reducing action. $GECWUG QH KVU UVTQPI CHſPKV[ HQT QZ[IGP CNWOKPKWO
KǀĞƌ ƚŚĞ ƉĞƌŝŽĚ͕ ŵĂŶLJ ŵŽƌĞ ŵĞƚĂůƐ acts as a strong reducing agent. It reduces ferric oxide, chromium
ǁĞƌĞ ĚŝƐĐŽǀĞƌĞĚ͘ oxide, etc. to the respective metal.
dĞĐŚŶŽůŽŐŝĐĂů ĚĞǀĞůŽƉŵĞŶƚƐ ůĞĚ ƚŽ Fe O + 2Al o 2Fe + Al O
3
2
3
2
ƚŚĞ ŶĞǁĞƌ ĂƉƉůŝĐĂƟŽŶƐ ŽĨ ŵĞƚĂůƐ͘ ferric oxide iron aluminium oxide
DĞƚĂůƐ ĂƌĞ ĐŽŵŵŽŶůLJ ƵƐĞĚ ŝŶ ƚŚƌĞĞ
ĚŝīĞƌĞŶƚ ĨŽƌŵƐ͗ Cr O + 2Al o 2Cr + Al O 3
2
3
2
;ĂͿ Ɛ ƉƵƌĞ ŵĞƚĂůƐ ;ďͿ Ɛ ĂůůŽLJƐ ;ĐͿ Ɛ chromium oxide chromium
ƚŚĞŝƌ ĐŽŵƉŽƵŶĚƐ Goldschmidt’s Aluminothermic welding process is based on this
property of aluminium.
Illustrative Questions
Q.1. Give reason for the following: Concentrated sodium hydroxide solution cannot be stored in aluminium
containers.
Ans. This is because aluminium is attacked by strong alkalis. With alkalis, aluminium gives soluble aluminates. For
example, with sodium hydroxide,
2Al + 2NaOH + 2H O o 2NaAlO 2 + 3H (g)
2
2
aluminium sodium sodium aluminate
hydroxide (soluble in water)
Therefore, concentrated sodium hydroxide cannot be stored in aluminium containers.
Q.2. Give reason: Concentrated nitric acid can be stored in aluminium containers.
Ans. Concentrated nitric acid forms a protective layer of Al O on the surface of aluminium. This layer of Al O
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2
3
2
prevents any further reaction between the acid and the metal. So, it is safe to store concentrated nitric acid in
aluminium containers.
Q.3. Explain why aluminium is more reactive than iron, yet there is less corrosion of aluminium when both are
exposed to the air.
Ans. Aluminium surface when exposed to air gets covered with a thin layer of Al O . This layer of Al O prevents any
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3
2
2
further reaction between aluminium and the air. Therefore, aluminium shows less corrosion than iron.
Q.4. What important properties of aluminium are responsible for its great demand in industry?
Ans. Some important properties of aluminium which are responsible for its great demand in industry are
ƒ High conductivity (both thermal and electrical)
ƒ Low density (or light weight)
ƒ Rust-proof nature
ƒ High tensile strength

ASSIGNMENT 4

Extraction, Refining and Properties of Aluminium
ϭ͘ 'ŝǀĞ ƚŚĞ ĐŚĞŵŝĐĂů ĐŽŵƉŽƐŝƟŽŶƐ ŽĨ ĐƌLJŽůŝƚĞ ĂŶĚ ďĂƵdžŝƚĞ͘
Ϯ͘ tŚLJ ŝƐ ĐƌLJŽůŝƚĞ ĂĚĚĞĚ ƚŽ ĂůƵŵŝŶĂ ŝŶ ƚŚĞ ĞdžƚƌĂĐƟŽŶ ŽĨ ĂůƵŵŝŶŝƵŵ͍
ϯ͘ EĂŵĞ ƚŚĞ ƌĞĚƵĐŝŶŐ ĂŐĞŶƚ ŝŶ ƚŚĞ ĨŽůůŽǁŝŶŐ ĐŚĞŵŝĐĂů ƌĞĂĐƟŽŶ͗
ϯDŶK н ϰ ů o ϯDŶ н Ϯ ů O
Ϯ
Ϯ ϯ
ϰ͘ tƌŝƚĞ Ă ĐŚĞŵŝĐĂů ƌĞĂĐƟŽŶ ƚŽ ƐŚŽǁ ƚŚĂƚ ĂůƵŵŝŶŝƵŵ ĐĂŶ ďĞ ƵƐĞĚ ĂƐ Ă ƌĞĚƵĐŝŶŐ ĂŐĞŶƚ͘
ϱ͘ ^ƚĂƚĞ ĂŶLJ ƚǁŽ ƵƐĞƐ ŽĨ ĂůƵŵŝŶŝƵŵ͘
ϲ͘ 'ŝǀĞ ƌĞĂƐŽŶ ĨŽƌ ƚŚĞ ĨŽůůŽǁŝŶŐ͗ ŽŶĐĞŶƚƌĂƚĞĚ ƐŽĚŝƵŵ ŚLJĚƌŽdžŝĚĞ ƐŽůƵƟŽŶ ĐĂŶŶŽƚ ďĞ ƐƚŽƌĞĚ ŝŶ ĂůƵŵŝŶŝƵŵ ĐŽŶƚĂŝŶĞƌƐ͘
ϳ͘ ůĞŵĞŶƚ ŚĂƐ ĞůĞĐƚƌŽŶŝĐ ĐŽŶĮŐƵƌĂƟŽŶ Ϯ͕ ϴ͕ ϯ ĂŶĚ ŽĐĐƵƌƐ ŝŶ ƚŚĞ ĞĂƌƚŚ͛Ɛ ĐƌƵƐƚ ĂƐ ŝƚƐ ŽdžŝĚĞ͘ O ͘ /ƚ ŝƐ ŵŽƌĞ ƌĞĂĐƟǀĞ ƚŚĂŶ
Ϯ ϯ
njŝŶĐ͘ ŶƐǁĞƌ ƚŚĞ ĨŽůůŽǁŝŶŐ͗