化學 2006 年 DSE、CE 選擇題（第 3 頁）

21.

Which of the following statements concerning the cleansing action of a detergent are correct ?

(1)It reduces the surface tension of water.

(2)It acts as an emulsifying agent.

(3)It reacts with grease to form soluble products.

22.

Which of the following reactions involve oxidation and reduction ?

(1)2KClO₃(s) → 2KCl(s) + 3O₂(g)

(2)Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l)

(3)H₂O₂(aq) + H₂SO₄(aq) + 2KI(aq) → K₂SO₄(aq) + I₂(aq) + 2H₂O(l)

23.

For each of the following questions, decide whether each of the two statements is true or false. If both are true, decide whether the second correctly explains the first.

A.Both statements are true and the 2nd statement is a correct explanation of the 1st statement.

B.Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.

C.The 1st statement is false but the 2nd statement is true.

D.Both statements are false.

1st statement	2nd statement
Solid citric acid reacts with magnesium to give hydrogen.	Citric acid contains ionisable hydrogen atoms.

24.

For each of the following questions, decide whether each of the two statements is true or false. If both are true, decide whether the second correctly explains the first.

A.Both statements are true and the 2nd statement is a correct explanation of the 1st statement.

B.Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.

C.The 1st statement is false but the 2nd statement is true.

D.Both statements are false.

1st statement	2nd statement
Potassium is a stronger reducing agent than sodium.	Potassium atoms lose electrons more readily than sodium atoms.

25.

For each of the following questions, decide whether each of the two statements is true or false. If both are true, decide whether the second correctly explains the first.

A.Both statements are true and the 2nd statement is a correct explanation of the 1st statement.

B.Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.

C.The 1st statement is false but the 2nd statement is true.

D.Both statements are false.

1st statement	2nd statement
In Hong Kong, taxis have switched from using diesel to using natural gas as fuel.	Burning natural gas poses less harm to the environment than burning diesel.

26.

Oxalic acid is a dibasic acid. 10.0 cm³ of an aqueous solution of oxalic acid requires 30.0 cm³ of 0.10 M KOH(aq) for complete neutralization. What is the concentration of the oxalic acid solution?

27.

Which of the following combinations is correct for a zinc-carbon cell ?

Anode	Cathode	Electrolyte
zinc	graphite	manganese(IV) oxide
zinc	graphite	ammonium chloride
graphite	zinc	manganese(IV) oxide
graphite	zinc	ammonium chloride

28.

In an experiment, a copper plate and a zinc plate are placed in a beaker containing dilute sulphuric acid. The two metal plate are touching each other as shown in the diagram below:

Which of the following statements correctly describes the observation in the experiment ?

29.

Which of the following changes occur after an aluminium article has been anodized ?

30.

The relative atomic mass of metal X is 55.8. 23.90 g of X is allowed to react with excess oxygen until X is completely oxidized. The mass of the metal oxides obtained is 34.18 g. What is the empirical formula of the oxide ? (Relative atomic mass: O = 16.0)