Module 5 Intro

1. Module 5 Intro

1.17. Page 2

Lesson 3

Module 5—Acids and Bases

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The following table contains information about two types of soft drinks—lemon-flavoured and cola. Use this information to answer the questions TR 1 to TR 4.

Soft Drink	Acid	Concentration of Acid	pH of Soft Drink
lemon flavoured	citric acid	0.7% W/V	2.6–2.9
cola	phosphoric acid	0.06% W/V	2.4–2.8

TR 1. Compare the pH of the two types of soft drinks shown in the table. Are the soft drinks of similar acidity? Support your answer by making specific reference to the data shown.

TR 2. Which soft drink contains more acid? By what factor?

TR 3. Calculate the hydronium-ion concentration for each soft drink. Identify which soft drink contains the higher concentration of hydronium ions.

TR 4. Compare the differences between the concentration of acid and the corresponding pH and [H3O+(aq)] for each soft drink. Describe whether the data follows an expected correlation or an unexpected correlation. Suggest a possible reason for the correlation shown.

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TR 1. Data may be compared using either of the following values:

Type of soft drink	Average pH	Approximate [H3O+(aq)]*
Lemon-flavoured	2.8	1.5 × 10–3 mol/L
Cola	2.6	2.5 × 10–3 mol/L

* Calculated using average pH

The pH values of the two soft drinks are quite similar in that they only differ by 0.2. Therefore, they have similar acidity in relation to the pH scale. The concentration of hydronium ions in each soft drink is similar since the values are of the same order of magnitude (exponent).

TR 2. The lemon-flavoured soft drink contains over ten times more acid than the cola.

TR 3. Refer to the table in the answer to question TR 1. The cola contains the higher hydronium-ion concentration.

TR 4. The soft drink with the higher concentration of acid has a higher pH. This result is not the expected correlation. A greater concentration of acid should result in a higher concentration of hydronium ions, formed by the reaction of the acid with water molecules. A possible explanation is that fewer citric acid particles react with water to form hydronium ions compared to phosphoric acid particles.