Passage VII

A carboxylic acid (CA) is a compound that contains a —COOH group. When a CA dissolves in H2O, it can dissociate, as shown below.

An atom's electronegativity (EN) indicates the atom's ability to attract electrons within a molecule (see Table 1). The presence of an electronegative atom in a CA, and the atom's proximity to the —COOH group, can affect the acidity of a CA.

Table 2 gives the pH of aqueous 1.00 M (mole per liter) CA solutions at 25°C. The CA in each solution is either an acetic acid or a propanoic acid (see Figure 1), where X and Y each represent an atom listed in Table 1.

Tables adapted from James G. Speight, Lange's Handbook of Chemistry, 16th ed.©2005 by McGraw-Hill, Inc.

40. Fluorine (F) is the most electronegative of all elements. Based on Tables 1 and 2, the pH of a 1.00 M aqueous solution of fluoroacetic acid at 25°C would most likely be:

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

Comparing table 1 & table 2, it can be seen that in the group of actic acid, the stronger the electronegtivity of the atoms contained, the stronger the corresponding acidity.

According to the question, Fluorine has the strongest electronegtivity, so its acidity should be greater than that of cholroacetic acid, that is, the pH is less than 1.44