Chem mc !!!

2009-03-29 6:02 am

1: An oxidation involves
(1) an increase in oxidation number.
(2) a gain of electron(s).
(3) a discharge.
A. (1)only
B. (2)only
C. (1)&(3)only
D. (2)&(3)only

2: A metal X displaces Y from a solution of its sulphate. Which of the following is/are correct?
(1) metal X would react more readily with water than does metal Y.
(2) the oxide of Y would be more difficult to be reduced than the oxide of X.
(3) metal Y is a stronger reducing agent than metal X.
A. (1)only
B. (2)only
C. (1)&(3)only
D. (2)&(3)only

3: Which of the following statements about chlorine bleach is INCORRECT?
A. it can improve home hygiene.
B. it is used as a sterilizing agent in swimming pools.
C. it can prevent the spread of certain diseases.
D. it is good for bleaching wool and silk.

4: If chlorine water is exposed to sunlight for several weeks, it will become
A. chloric acid.
B. hydrochloric acid.
C. water.
D. hypochlorous acid.

5: Which of the following would NOT decolorize acidified potassium permanganate solution?
(1) aqueous solution of sulphur dioxide.
(2) sodium hypochlorite solution.
(3) potassium sulphite solution.
A. (1)only
B. (2)only
C. (1)&(3)only
D. (2)&(3)only

6: Which of the following about the bleaching action of sulphur dioxide is/are correct?
(1) it is especially good for bleaching natural fibres.
(2) the bleaching action lasts for a long period of time.
(3) it bleaches by oxidation.
A. (1)only
B. (2)only
C. (1)&(3)only
D. (2)&(3)only

俾埋 explain plz ^^

回答 (1)

老爺子

2009-03-29 8:17 am

✔ 最佳答案

1:
The answer is A.

(1) is correct.

(2) is incorrect.
An oxidation involves the loss of electrons.
e.g. Fe2+(aq) → Fe3+(aq) + e-

(3) is incorrect.
e.g. Fe2+(aq) → Fe3+(aq) + e- is not a discharge.

2:
The answer is A.

A more reactive displaces a less reactive metal. Hence, X is more reactive than Y.

(1) is correct.
The more reactive metal (X) reacts with water more readily.

(2) is incorrect.
The oxide of a less reactive metal (Y) is reduced more readily.

(3) is incorrect.
A less reactive metal (Y) is a weaker reducing agent.

3:
The answer is D.

A, and C are correct.
Chlorine can be used as a disinfectant.

B is also correct.

D is in correct.
Chlorine can destroy the structure of silk.

4:
The answer is B.

Cl2(aq) + H2O(l) ≒ HCl(aq) + HOCl(aq)
2HOCl(aq) → HCl(aq) + O2(g)

5:
The answer is B.

(1) is incorrect.
Sulphur dioxide solution is a reducing agent, which can reduce acidified KMnO4 solution to colourless Mn2+(aq) ions.
5SO2(aq) + 2MnO4-(aq) + 2H2O(aq) → 5SO42-(aq) + 2Mn2+(aq) + 4H+(aq)

(2) is correct.
Sodium hypochlorite solution is an oxidizing agent, which cannot reduce acidified KMnO4 solution.

(3) is incorrect.
Potassium sulphite solution is a reducing agent, which can reduce acidified KMnO4 solution to colourless Mn2+(aq) ions.
5SO32-(aq) + 2MnO4-(aq) + 6H+(aq) → 5SO42-(aq) + 2Mn2+(aq) + 3H2O(l)

6:
The answer is A.

(1) is correct.

(2) is incorrect.
Oxygen in air can oxidize the bleached compounds back to dyes.

(3) is incorrect.
It bleaches by reduction.
=

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