acids and alkalis (M.C.)

Tieria

2009-05-02 9:49 pm

1. A sample of hydrochloric acid and a sample of ethanoic acid both have a pH value of 2. It can be concluded that:
A. they are equally strong.
B. They are of the same concentration.
C. The volume of the two samples of acids are the same.
D. They contain the same concentration of hydrogen ions.

※ 試解釋各點對與錯的原因※

2. Which of the following statements concerning citric acid is/are correct?
(1) It is a strong acid.
(2) It is present in oranges.
(3) It exists as a solid at room temperature.

A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only

※試解釋第(3)點對與錯的原因※

回答 (1)

老爺子

2009-05-03 12:05 am

✔ 最佳答案

1.
The answer is D.

D is correct.
pH is a measure of the concentration of H+(aq) ions. If two solutions have the same pH value, the two solutions have the same concentration of H+(aq) ions.

A and B are incorrect.
A more concentrated weak acid (e.g. ethanoic acid) and a less concentrated strong acid (e.g, hydrochloric acid) would have the same concentration of H+(aq) ions, i.e. the same pH value.

C is incorrect.
pH value is independent of the volume of the solution. For example, if a solution of pH 2 is divided into two portions, each portion remains pH 2.

2.
The answer is D.

(1) is incorrect.
Citric acid is a weak acid.

(2) is correct.
Citric acid is present in fruits like lemons and oranges.

(3) is correct.
Pure citric acid is molecular with molecular formula C6H8O7. The intermolecular forces between citric molecules are great enough to hold the citric acid molecules to be a solid at room temperature.
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