Question

Define pH. What pH range is considered acidic? Basic? Neutral?

Short answer

pH measures the concentration of hydrogen ions using a scale from 0 to 14; acid is pH < 7, neutral is pH = 7, and basic is pH > 7.

Step-by-step solution

Defining pH

pH is a measure of the hydrogen ion concentration (\( [H^+] \) in a solution. The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution. The formula to calculate pH is \( pH = -\log_{10} [H^+] \) where \( [H^+] \) is the hydrogen ion concentration in moles per liter.

Determining pH ranges for acidity, neutrality, and basicity

The pH scale typically runs from 0 to 14. A pH less than 7 is considered acidic, which means a higher concentration of hydrogen ions. A pH of 7 is considered neutral, which is the pH of pure water. A pH greater than 7 is considered basic (or alkaline), indicating a lower concentration of hydrogen ions.

Key concepts

Hydrogen Ion Concentration

Understanding the concept of hydrogen ion concentration (\( [H^+] \) is crucial in chemistry. It refers to the amount of hydrogen ions present in a solution. Since hydrogen ions are simply protons (\( H^+ \) ions), this concentration determines the acidity or basicity of the solution. A higher concentration of hydrogen ions signifies an acidic solution, while a lower concentration indicates a basic solution.

Why does this matter? The behavior of hydrogen ions in a solution can influence chemical reactions, biological systems, and even environmental processes. For example, our blood has a finely-tuned hydrogen ion concentration, which if altered, can affect our health. In the environment, rainfall with high hydrogen ion concentration, known as acid rain, can damage ecosystems. Hence, understanding and measuring hydrogen ion concentration is vital in various fields of science.

Acidity and Basicity

Acidity and basicity are fundamental concepts that describe the nature of a solution. These properties are directly linked to the hydrogen ion concentration discussed earlier. Acidity refers to the presence of excess hydrogen ions (\( [H^+] > 10^{-7} \ M \) ) and is measured by a pH value that falls below 7. On the other hand, basicity is characterized by a scarcity of hydrogen ions (\( [H^+] < 10^{-7} \ M \) ) and is expressed by a pH value above 7.

• Acidic solutions are often sour to taste, can conduct electricity due to the presence of ions, and can react with metals.
• Basic solutions, also known as alkaline solutions, feel slippery to touch and can neutralize acids.
• Neutral solutions exhibit a balance in the concentration of hydrogen ions and hydroxide ions, with a pH value exactly at 7, like pure water.

This understanding is not just academic—knowing whether a substance is acidic or basic can influence its handling, storage, and disposal.

pH Calculation

The calculation of pH is a mathematical representation of the acidity or basicity of a solution. It is determined by the formula \( pH = -\log_{10} [H^+] \) which involves taking the negative logarithm (base 10) of the hydrogen ion concentration. This formula translates the potentially complex and wide-ranging hydrogen ion concentrations into a simple, easy-to-understand scale from 0 to 14.

To make things easier, let's imagine you have a solution with a hydrogen ion concentration of \( 1 \times 10^{-3} \) M. Using the pH formula, we have \( pH = -\log_{10} (1 \times 10^{-3}) = 3 \). This means the solution is acidic since the pH is less than 7.

Remember, due to the logarithmic nature of the pH scale, each one-unit change in pH equals a tenfold change in hydrogen ion concentration. This helps us to easily compare the relative acidity or basicity of solutions. Additionally, precise pH calculation can be critical in applications like medicine, agriculture, and environmental science.