Chem mc !!

2009-03-26 4:07 am

1: Which of the following processes requires a catalyst?
A. preparation of ethanoate from ethanoic acid and ethanol.
B. conversion of sulphur trioxide to concentrated sulphuric acid.
C. manufacture of chlorine bleach from brine.
D. reduction of iron(III) oxide to iron.

2: Which of the following processes is endothermic?
A. cracking of petroleum fractions.
B. fermentation of glucose solution.
C. manufacture of ammonia by the Haber process.
D. oxidation of sulphur dioxide to sulphur troxide in the contact process.

3: Which of the following uses of sulphuric acid is/are correct?
(1) manufacture of soaps.
(2) manufacture of paint additives.
(3) manufacture of fertilizers.
A. (1)only B. (2)only
C. (1)&(3)only D. (2)&(3)only

4: Which of the following reactions does NOT require the use of a catalyst?
A. conversion of ammonia to nitrogen monoxide.
B. hydration of ethene to give ethanol.
C. oxidation of ethanol to ethanoic acid.
D. fermentation of glucose to give ethanol.

5: In a boiler using hard water, scale is deposited on its interior after a period of time. The scale consists mainly of metal carbonates. Which of the following substances can be used to remove the boiler scale?
A. soapless detergent
B. chlorine bleach
C. sodium hydroxide solution
D. vinegar

6: Which of the following statements concerning sodium hydroxide is INCORRECT?
A. it is manufactured by treating sodium with water.
B. its concentrated solution is corrosive.
C. it is used in the manufacture of soapless detergents.
D. it absorbs carbon dioxide when exposed to air.

7: Which of the following statements concerning the Haber process is INCORRECT?
A. nitrogen and hydrogen undergo complete reaction in the reaction chamber.
B. nitrogen and hydrogen are compressed to about 200 atm before they are allowed to undergo reaction.
C. the process is operated at about 500^c.
D. the reaction between nitrogen and hydrogen is exothermic.

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回答 (1)

老爺子

2009-03-26 8:06 am

✔ 最佳答案

1:
The answer is A.

A is esterification, in which concentrated sulphuric acid is used as a catalyst.
The other three reactions do not need any catalyst.

2:
The answer is A.

Cracking (A) is the process of dividing large hydrocarbon molecules into smaller hydrocarbon molecules or hydrogen. In cracking, energy is needed to break the bonds in the large hydrocarbon molecules.

The other three reaction are exothermic.

3.
The answer D.

(1) is incorrect. Soaps are made from the reaction of a vegetable oil (or an animal fat) and concentrated sodium hydroxide solution.

(2) is correct. Paint additives such as BaSO4 and CaSO4 are made by using sulphuric acid.

(3) is correct. Fertilizers such as (NH4)2SO4 are made by using sulphuric acid.

4:
The answer is C.

In C, ethanol is oxidized to give ethanoic acid by reacting with acidified potassium dichromate solution. Both sulphuric acid and potassium dichromate solution are reactants, and no catalyst is needed.

In A, B and D, the catalysts are platinum, acid (usually phosphoric acid) and enzyme from yeast respectively.

5:
The acid is D.

The metal carbonates that form the scale is water insoluble. Vinegar is the solution of dilute ethanoic acid. Metal carbonates react with dilute ethanoic acid in the vinegar to form a soluble ethanol, carbon dioxide gas and water.

6:
The answer is A.

The method stated in A is too dangerous and expensive. Sodium hydroxide is usually manufactured by electrolysis of brine instead.

7:
The answer A.

The reaction is incomplete, because the reaction is reversible and the yield is only about 15%.
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