[4 MARCK QUESTION]

Question 14 Marks

Name an alloy of
(i) iron used in manufacturing of surgical instruments.
(ii) lead used in joining metals for electric welding.
(iii) copper used in making household vessels.
(iv) aluminium used in making aircraft parts.
Write one property of each associated with the use.

Answer

(i) Stainless steel - It is not oxidised (or rust) by the attack of acids or bases or water.
(ii) Solder - low melting point
(iii) Brass - lustrous and malleable
(iv) Duralumin - light weight

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Question 24 Marks

Two ores A and B were taken. On heating ore A gives CO₂ whereas, ore B gives SO₂. What steps will you take to convert them into metals?

Answer

Ore A gives CO₂ on heating, hence, it is a carbonate ore.
Steps involved in extraction of metal from ore A:
(i) Calcination - Ore is heated in a limited supply of air to obtain a metal oxide.
(ii) Reduction by C - The metal oxide is reduced with coke to obtain metal.
Ore B gives SO₂, hence, it is a sulphide ore.
The steps involved in the extraction of metal from ore B:
(i) Roasting - Ore is heated in the presence of air to obtain a metal oxide.
(ii) Reduction by C - The metal oxide is reduced to metal by carbon.

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Question 34 Marks

From the list of concentrated oxide ores mentioned here, identify their reduction processes. Write the chemical equations involved.
(i) ZnO, (ii) HgO, (iii) Cr₂O₃, (iv) CuO

Answer

(i) ZnO is reduced by coke at high temperature
$ZnO + C \xrightarrow{\Delta} Zn + CO$
(ii) HgO is reduced by heating alone.
$2 HgO \xrightarrow{\Delta} 2 Hg + O _2$
(iii) Cr₂O₃ is reduced by using aluminium as a reducing agent
Cr₂O₃+2Al → Al₂O₃+ 2Cr
(iv) CuO is reduced by using hydrogen gas as reducing agent
CuO + H₂→ Cu + H₂O

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Question 44 Marks

Bauxite is the chief ore of aluminium. The ore is first purified and then aluminium metal is extracted by electrolyic reduction.
(i) Write three balanced equations for the purification of ore by Hall's process.
(ii) Name the chemical used for dissolving pure aluminium oxide. In which state the chemical is used?
(iii) Write equations for the reactions taking place at the anode in a electrolytic tank.

Answer

(i)$\begin{array}{l} Al _2 O _3 \cdot 2 H _2 O + Na _2 CO _3 \xrightarrow{\text { heat }}
2 NaAlO _2+2 H _2 O + CO _2(g) \\ 2 NaAlO _2+3 H _2 O + CO _2 \longrightarrow Na _2 CO _3+2 Al ( OH )_3( ppt ) \\
2 Al ( OH )_3 \xrightarrow{1100^{\circ} C } Al _2 O _3+3 H _2 O \end{array}$
(ii) The chemical is cryolite. It is used in the fused state.
(iii) 0^2- - 2e^-→ [0]
C + 2[0] → CO₂

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Chemistry [4 MARCK QUESTION]

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