Anonymous
Anonymous asked in 科學及數學化學 · 10 years ago

F.4 Chem Questions (Alkali)

Directions: Question 1-3 refer to the following options:

(1)CuO

(2)Ca(OH)2

(3)CaCO3

(4)Li

1. Which are bases?

A. (1) and (2) only

B. (2) and (4) only

C. (3) and (4) only

D. (1),(2) and (3) only

2. Which is/are alkali(s)?

A. (2) only

B. (1) and (3) only

C. (2) and (4) only

D. (1),(3) and (4) only

3. Which would give an alkaline aqueous solution?

A. (1) and (2) only

B. (2) and (3) only

C. (2) and (4) only

D. (3) and (4) only

我同埋想問下第2,3條問題有咩分別?

alkali is soluble base,,當然係aqueous~~

1 Answer

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  • 10 years ago
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    First, you should know the definition of base.

    A base is a compound which reacts with an acid to give a salt and water only.

    (Note: At F.4 level, hydroxides or oxides of metal are usually called as base.

    Word equation: Acid + Base --> salt + water

    For question 1, copper oxide and calcium hydroxide are the answers.

    Answer is A.

    _____________________________________________________________

    For question 2, the definition of alkali is soluble base as you mentioned.

    Only calcium hydroxide is a base that soluble in water.

    Answer is A.

    _____________________________________________________________

    For question 3, the phrase "give alkaline aqueous solution" is asking you which substance when dissolved in water will give an solution of pH value greater than 7.

    For,

    (1) CuO, it is insoluble in water.

    (2) Ca(OH)2, it is a soluble base. When it is reacted with water, it will be diluted. It is still an aqueous alkaline solution.

    (3) CaCO3 (main ingredient of chalk for writing blackboard), it is insolube in water.

    (4) Li, it belongs to group 1 which is a group of ALKALI metal. When lithium reacts with water,

    Li (s) + H2O (l) ---> LiOH (aq) + H2 (g)

    Lithium hydroxide is formed which is an aqueous alkaline solution.

    Answer is C.

    Hence, question 2 & 3 are asking for different things.

    Hope my explanations help.

    Source(s): myself.
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