Chem MC 7條

2009-03-19 5:14 am

1: Which of the following statements is INCORRECT?
A. Tin is used for making food cans.
B Sulphur acid is used for making soap.
C. Ammonium chloride is used for making dry cells.
D. Chlorine is used for sterilizing drinking water.

2:A solution of chlorine in tetrachloromethane is shaken with an aqueous solution of a compound X in atest. On standing, two layers are formed in the test tube and the lower layer is violet in colour. X may be
A. sodium fluoride B. sodium bromide
C. sodium iodide D. sodium sulphite

3: Which of the following substances, when mixed, will undergo a reaction?
A. vinegar and anti-acid
B. bleach and anti-acid
C. vinegar and table salt
D. bleach and table salt

4: A gardener bought a bag of potassium nitrate and a bag of ammonium sulphate, to be used as fertilizers. He forgot to label the bags. Which of the following tests would enable him to distinguish between the two chemicals?
A. heating each chemical with dilute sulphuric acid
B. heating each chemical with sodium chloride solution
C. heating each chemical with potassium hydroxide solution
D. heating each chemical with acidified potassium dichromate solution

5: In which of the following reactions does sulphur dioxide act as a reducing agent?
(1) the production of sulphuric acid in the contact process
(2) the bleaching of a red petal
(3) the decolorization of bromine water
A. (1)&(2)only B. (1)&(3)only
C. (2)&(3)only D. (1),(2)&(3)

6: Which of the following statements concerning the Haber Process is INCORRECT?
A. Iron is used as a catalyst in the process
B. The reaction involved in the process is reversible
C. The reaction involved in the process is exothermic
D. The process is performed at one atmosphere pressure

7: Which of the following elements are essential for plant growth?
(1) potassium (2) phosphorus
(3) silicon (4) nitrogen
A. (1),(2)&(3)only B. (1),(2)&(4)only
C. (1),(3)&(4)only D. (2),(3)&(4)only

俾埋解釋ㄚ Thx ^^

回答 (1)

老爺子

2009-03-19 6:33 am

✔ 最佳答案

1:
The answer is B.

B is incorrect. To make soap, the mixture of a vegetable oil (or an animal fat) and conc. NaOH is heated for some time, followed by salting out the soap by using conc. NaCl when the reaction mixture is cooled.

2:
The answer is C.

The lower layer is the CCl4 layer, which turns violet in the presence of I2.

A is incorrect.
Chlorine does not react with sodium fluoride solution.

B is incorrect.
Chlorine oxidizes bromide ions to give Br2 which dissolves in CCl4 to give an orange solution, but not violet.

C is correct.
Chlorine oxidizes iodide ions to give I2 which dissolves in CCl4 to give a violet solution.

D is incorrect.
Chlorine can oxidize sodium sulphite solution to sodium sulphate solution.
Cl2(aq) + SO32-(aq) + H2O(l) → 2Cl-(aq) + SO42-(aq) + 2H+(aq)

3:
The answer is A.

Vinegar is the dilute solution of ethanoic acid. An anti-acid can neutralize acids.
B, C and D do not give any reaction.

4.
The answer is C.

On heating, ammonium sulphate reacts with potassium hydroxide to give ammonia gas which turns moist red litmus paper to blue.
(NH4)2SO4 + 2KOH → K2SO4 + 2H2O + 2NH3
Potassium nitrate does not react with potassium hydroxide.

Both compounds do not react with dilute sulphuric acid (A), sodium chloride solution (B) or acidified potassium dichromate solution (C).

5:
The answer of D.

(1) is correct.
Sulphur dioxide is oxidized, because the oxidation number of S increases from +4 to +6.

(2) is correct.
Sulphur dioxide bleaches by reducing the dye.
SO2 + 2H2O + dye → 2H+(aq) + SO42-(aq) + [dye - O]

(3) is correct.
Br2(aq) + SO2(aq) + 2H2O(l) → 2Br-(aq) + SO42-(aq) + 4H+(aq)
Br2 is reduced, because the oxidation number of Br decreases from 0 to -1.
SO2 is oxidized, because the oxidation number of S increases from +4 to +6.

6:
The answer is D.

D is incorrect. The process is performed at 200 atm, but not 1 atm.
All of A, B and C are correct.

7:
The answer is B.

Plants needs potassium, phosphorus and nitrogen, but not silicon.
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