Problem 3 - Chemistry A Guided Inquiry

Question

What values of pH characterize: a) an acidic solution? b) a basic solution?

Step-by-Step Solution

Answer

a) An acidic solution is characterized by a pH less than 7. b) A basic solution is characterized by a pH greater than 7.

Step 1 - Understand the pH scale

pH is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the molar concentration of hydrogen ions in the solution. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic.

Step 2 - Characterizing an acidic solution

An acidic solution is one where the pH is less than 7. This means there is a higher concentration of hydrogen ions in the solution.

Step 3 - Characterizing a basic solution

A basic solution is one where the pH is greater than 7. This means there is a lower concentration of hydrogen ions, or a higher concentration of hydroxide ions in the solution.

Key Concepts

Understanding the pH Scale

The pH scale is a fundamental concept in chemistry, providing a measure of the acidity or basicity of a solution. Its values range from 0 to 14. A pH value below 7 indicates an acidic solution, whereas a pH above 7 signals a basic solution. Neutral solutions — such as pure water — have a pH of exactly 7.

It's important to note that the pH scale is logarithmic, meaning that each unit change in pH represents a tenfold change in hydrogen ion concentration ([H^+]). So, for example, a solution with a pH of 6 has ten times more hydrogen ions than a solution with a pH of 7.

Acidic Solutions

An acidic solution is characterized by a pH value less than 7. This lower pH value comes from a higher concentration of positively charged hydrogen ions ([H^+]). Generally, the more hydrogen ions present, the more acidic the solution. Common examples of acidic solutions include vinegar and lemon juice.

These solutions donate hydrogen ions to reactions, which is how they display their characteristic properties, such as sour taste and the ability to dissolve metals.

Basic Solutions

Conversely, a basic solution has a pH value greater than 7. This reflects a lower concentration of hydrogen ions ([H^+]), or alternatively, a higher concentration of hydroxide ions ([OH^-]). Basic solutions can have a slippery feel and are found in products like bleach and baking soda.

In chemical reactions, basic solutions often accept hydrogen ions, which results in the neutralization of acids, a process frequently observed in titrations.

Characterizing Acidity and Basicity

Characterizing the acidity or basicity of a solution is done by measuring its pH. The further from pH 7 a solution's pH value is, the more acidic or basic it is. Acidity and basicity are important because they can affect reaction rates, product formation, and biological systems.

Maintaining the correct pH is crucial in many industrial and biological processes. For instance, human blood should stay within a narrow pH range around 7.4. Deviations in pH can affect the activity of enzymes and even harm cells. Therefore, the pH scale is not just an abstract concept, it's a critical parameter in both science and daily life.