Chemistry
Explain the following:
(a) Zinc is used to cover iron so as to prevent rusting of iron. Why?
(b) In construction work, why is the alloy of aluminium–duralumin used rather than pure aluminium?
Metallurgy
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Answer
(a) As zinc is more reactive than iron, hence it forms a dense and impermeable layer of zinc oxide over iron which protects the iron beneath from rusting.
(b) As duralumin has strength up to six times greater than pure aluminium hence, alloy of aluminium–duralumin is used rather than pure aluminium in construction work.
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Related Questions
(a) A to F below relate to the source and extraction of either zinc or aluminium:
A. Bauxite
B. Coke
C. Cryolite
D. Froth floatation
E. Sodium hydroxide solution
F. Zinc blende
(i) Write down the three letters each from the above list which are relevant to
- Zinc
- Aluminium
(ii) Fill in the blanks using the most appropriate words from A to F.
The ore from which aluminium is extracted must first be treated with …………… so that pure aluminium oxide can be obtained.
Pure aluminium oxide is dissolved in …………… to make a conducting solution.
(iii) Write the formula of cryolite.
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(a) Powdered coke is sprinkled over the electrolytic mixture undergoing electrolytic reduction.
(b) Graphite anodes are continuously replaced during the electrolysis.
(c) Cryolite and fluorspar must be added to the electrolytic mixture.
(d) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.
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