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Question : 37
Total: 39
On the basis of reactivity metals are grouped into three categories:
(i) Metals of low reactivity
(ii) Metals of medium reactivity
(iii) Metals of high reactivity
Therefore metals are extracted in pure form from their ores on the basis of their chemical properties.
Metals of high reactivity are extracted from their ores by electrolysis of the molten ore.
Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.
(a) Name the process of reduction used for a metal that gives vigorous reaction with air and water both.
(b) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide? Why?
(c) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.
OR
(c) Differentiate between roasting and calcination giving chemical equation for each.
(i) Metals of low reactivity
(ii) Metals of medium reactivity
(iii) Metals of high reactivity
Therefore metals are extracted in pure form from their ores on the basis of their chemical properties.
Metals of high reactivity are extracted from their ores by electrolysis of the molten ore.
Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.
(a) Name the process of reduction used for a metal that gives vigorous reaction with air and water both.
(b) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide? Why?
(c) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.
OR
(c) Differentiate between roasting and calcination giving chemical equation for each.
Solution:
(a) The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode).
(b) Aluminium has greater affinity for oxygen than for carbon, therefore carbon cannot reduce alumina to aluminium.
(c) Cinnabar( HgS ) ( HgO )
2 HgS ( s ) + 3 O 2 ( g )
2 HgO ( s ) + 2 SO 2 ( g )
2 HgO ( s )
2 Hg ( l ) + O 2 ( g )
OR
(c) Difference between roasting and calcination are:
Calcination: The process of conversion of a concentrated ore into its oxide by heating in absence of air below its melting point is called calcination. It is usually done for hydroxide and carbonate ores. Example:
(c) Difference between roasting and calcination are:
Calcination: The process of conversion of a concentrated ore into its oxide by heating in absence of air below its melting point is called calcination. It is usually done for hydroxide and carbonate ores. Example:
MgCO 3
MgO + CO 2
Here, magnesium carbonate is heated in the absence of air to gain magnesium oxide as the product.
Roasting: The process of metallurgy where an ore is converted into its oxide by heating it above its melting point in the presence of excess air is called roasting. Usually, sulphide is converted to an oxide, and Sulphur is released as sulphur dioxide, a gas.
Example:
2 ZnS + 3 O 2
ZnO + 2 SO 2
Here, zinc sulphide is converted to zinc oxide, and sulphur is released as sulphur dioxide, a gas.
(b) Aluminium has greater affinity for oxygen than for carbon, therefore carbon cannot reduce alumina to aluminium.
(c) Cinnabar
OR
(c) Difference between roasting and calcination are:
Calcination: The process of conversion of a concentrated ore into its oxide by heating in absence of air below its melting point is called calcination. It is usually done for hydroxide and carbonate ores. Example:
(c) Difference between roasting and calcination are:
Calcination: The process of conversion of a concentrated ore into its oxide by heating in absence of air below its melting point is called calcination. It is usually done for hydroxide and carbonate ores. Example:
Here, magnesium carbonate is heated in the absence of air to gain magnesium oxide as the product.
Roasting: The process of metallurgy where an ore is converted into its oxide by heating it above its melting point in the presence of excess air is called roasting. Usually, sulphide is converted to an oxide, and Sulphur is released as sulphur dioxide, a gas.
Example:
Here, zinc sulphide is converted to zinc oxide, and sulphur is released as sulphur dioxide, a gas.
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