Q98 of 400 Page 195

Four metals P, Q R and S are all obtained by the reduction of their oxides with carbon. Metal P is used to form a thin layer over the sheets of metal S to prevent its corrosion. Metal Q is used for electroplating tiffin boxes made of metal S whereas metal R is used in making car batteries. Metals Q and R form an alloy called solder. What are metals P, Q R and S? How have you arrived at this conclusion?

Metal P is zinc; Metal Q is tin; Metal R is lead; Metal S is iron; Metal P (zinc) is used to form a thin layer on metal S (iron) to prevent its corrosion; Metal Q (tin) is used for electroplating tiffin boxes made of metal S (iron); Metal R (lead) is used in making car batteries; Metals Q (tin) and R (lead) form an alloy called solder.

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96 A metal X which is resistant to corrosion is produced by the electrolysis of its molten oxide whereas another metal Y which is also resistant to corrosion is produced by the reduction of its oxide with carbon. Metal X can be used in powder form in thermite welding whereas metal Y is used in making cathodes of ordinary dry cells.

(a) Name the metals X and Y.


(b) Which of the two metals is more reactive: X or Y?


(c) Name one ore or metal X. Also write its chemical formula.


(d) Name one ore of metal Y. Also write its chemical formula.


(e) Name one alloy of metal X and one alloy of metal Y.

 97 When an object made of metal A is kept in air for a considerable time, it loses its shine and becomes almost black due to the formation of a layer of substance B. When an object made of another metal C is kept in damp air for a considerable time, it gets covered with a green layer of substance D. Metal A is the best conductor of electricity whereas metal C is the next best conductor of electricity.

(a) What is metal A?


(b) What is metal C?


(c) Name the substance B.


(d) Name the substance D.


(e) What type of chemical can be used to remove the green layer from metal C and clean it? Why?

 99 A black metal oxide X02 is used as a catalyst in the preparation of oxygen gas from potassium chlorate. The oxide XO2 is also used in ordinary dry cells. The metal oxide XO2 cannot be reduced satisfactorily with carbon to form metal X.

(a) Name the metal X.


(b) Name the metal oxide XO2


(c) Which reducing agent can be used to reduce XO2 to obtain metal X?


(d) Name another metal which can also be extracted by the reduction of its oxide with the above reducing agent.

 100 Metals X and Y can be recovered from the anode mud left behind after the electrolytic refining of copper metal. The coins made of metal X look new even after several years of use but the coins made of metal Y lose their shine gradually and get blackened soon. When metal X is alloyed with a small amount of metal Y, it becomes hard and hence suitable for making ornaments. What are metals X and Y? Also state the colour of metal X.