CBSE Class 12 Chemistry Isolation Of Elements VBQs

Chapter-6

GENERAL PRINCIPALS AND PROCEESS OF ISOLATION OF ELEMENTS

Question. A washer woman, while washing a miner’s overalls, she noticed that sand and similar dirt fell to the bottom of the wash tub. What was peculiar, the copper bearing compounds that had come to the cloths from mines were caught in soap suds and so they come to the top. One of her client was chemistry teacher Mrs Geetha. The washer woman told her experience to Mrs Geetha who thought that the idea could be used for separating coper compounds from rocks and Earth materials on large scale. This way an invention was born.

(1) Which method was invented by above experience?

(2) What values were possessed by washer women?

(3) What was the effect of the above invention?

Answer: (i) froth-floatation process for sulphide ores of copper

(ii) scientific temperament, attentive to observations, innovative mind.

(iii) invention of the froth-flotation process made cooper mining profitable even from the low grade ores. World production of copper increased and the metal became cheaper.

Question. In roasting, the ore is heated in regular amount of air in a furnace at a below the melting point of the metal. Metal sulphide gets converted into metal oxides and sulphur dioxide gas is formed which is an air pollutant. It also leads to the formation of the acid rain which is harmful for crops and building made up of marble. 1) Where should we have industry using roasting process in metallurgy? Give reason.

2) How can we use sulphur dioxide gas?

3) What are the uses of sulphuric acid? How can it help in national economy?

Answer: (i) These industries should be away from highly populated area because air pollution due to sulphur dioxide gas is harmful for all living beings.

(ii) Sulphur dioxide gas can be used for the manufacture of sulphuric acid.

(iii) It is used in fertilizers, detergents and medical industries. Sulphuric acid is king of chemicals. It is used in fertilizers, petroleum refining, lead storage batteries, metallurgy, electroplating and galvanization. It is used in lot of Industries; therefore, it helps in national economy of country like India which is mainly dependent upon agriculture and industries.

Question. Gold occurs in free state in earth’s crust. It is leached with dilute solution of potassium cyanide to form a soluble complex. Gold is smuggled in the form of this complex compound as it is liquid like lime water and can’t be detected even by X-ray. Customs officers found it extra ordinary heavy liquid and sent into chemistry lab.

(1) How will chemistry find that it contains potassium dicyanoaurate (I)?

(2) Should potassium cyanide be readily available?

(3) How can you prevent smuggling of gold by this process? What values are not processed by smugglers? 

Answer: (i) If zinc is added to gold metal will be formed.

(ii) No, potassium cyanide should not be readily available. It should only be supplied to industries and research labs with permit.

 (iii) liquid should not be allowed to be transported without proper certification. Smugglers are enemies for the country. They are not honest and sincere about these countries.

Question. Magnesium is more electropositive than aluminium, therefore, it can reduce alumina thermodynamically but in India aluminium is being extracted by electrolytic reduction and not chemical reduction.

1) Under what conditions magnesium can reduce alumina?

2) Although thermodynamically feasible, in practice, magnesium metals is not used to reduce alumina. Explain.

Answer: (i) magnesium can reduce alumina at nearly 1350 degree or 1625 kelvin.

                      3Mg + Al₂O₃ → 3Mgo + 2Al.

(ii) it is because reduction can be carried out only above 1600 kelvin which is uneconomical.

(iii) it will help to improve national economy as lot of industries are based on aluminium. Its cost of production will be reduced and help common man.

Question. Metals are very useful in our daily life. Aluminium power us used in white paints. It is used as a reducing agent. Alloys containing aluminium, being light,are very useful. Utensils of aluminium are more popular then utensils of brass. Metals like silver, gold, iron, copper, zinc are very useful in our daily life.

1) Which metal foils are used as wrappers for chocolates, medicines, chapaties, etc.?

2) Why are aluminium vessels preferred over copper and bronze vessels?

3) What values are possessed by people using aluminium instead of copper?

Answer: (i) aluminium wrapper.

(ii) it is because aluminium does not corroded whereas, copper and bronze form aq green layer on their surface which is due to the formation CuCO₃.Cu(OH)₂ which is poisonous.

(iii) They are conscious of their health. Secondly, aluminum is cheaper than copper, so it will help to improve national economy.

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