Question

On the \(\mathrm{pH}\) scale, which numbers indicate a basic solution? An acidic solution? A neutral solution? What makes a solution basic, acidic, or neutral? (pages \(27-29\) )

Short answer

On the pH scale, a basic solution has a value greater than 7, an acidic solution has a value less than 7, and a neutral solution has a value of 7. A solution is considered basic if the concentration of hydroxide ions (OH-) is greater than hydrogen ions (H+), acidic if the concentration of hydrogen ions (H+) is greater than hydroxide ions (OH-), and neutral if the concentrations of both ions are equal. Basic solutions taste bitter and feel slippery, acidic solutions taste sour and can be corrosive, while neutral solutions have no characteristic taste and properties.

Step-by-step solution

Understanding the pH scale

The pH scale is a measurement of the acidity or basicity of a solution. It ranges from 0 to 14, with 7 being the middle value that represents a neutral solution. Values below 7 indicate an acidic solution, and values above 7 indicate a basic (or alkaline) solution.

Identifying basic, acidic, and neutral solutions

On the pH scale: - A basic solution has a pH value greater than 7. - An acidic solution has a pH value less than 7. - A neutral solution has a pH value of 7.

Characteristics of basic, acidic, and neutral solutions

A solution is considered basic, acidic, or neutral depending on the concentration of hydrogen ions (H+) and hydroxide ions (OH-) present in the solution: 1. Basic solution: In a basic solution, the concentration of hydroxide ions (OH-) is greater than the concentration of hydrogen ions (H+). As a result, the pH value will be greater than 7. Basic solutions usually taste bitter and feel slippery. 2. Acidic solution: In an acidic solution, the concentration of hydrogen ions (H+) is greater than the concentration of hydroxide ions (OH-). As a result, the pH value will be less than 7. Acidic solutions usually taste sour and can be corrosive. 3. Neutral solution: In a neutral solution, the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-). As a result, the pH value will be 7. Neutral solutions have no characteristic taste and don't carry the properties of an acidic or basic solution.

Key concepts

Acidic Solution

An acidic solution is one where the concentration of hydrogen ions \( ext{H}^+\) exceeds that of hydroxide ions \( ext{OH}^-\).
On the pH scale, acidic solutions have a pH value less than 7.
This excess of hydrogen ions makes acidic solutions taste sour, like lemon juice or vinegar.
Common examples include citrus fruits, stomach acid (hydrochloric acid), and battery acid. When considering the properties of acids, remember:

• They can conduct electricity because they ionize in water.
• They react with metals to produce hydrogen gas.
• They turn blue litmus paper red.

These properties are due to the way acids dissociate in water to release \( ext{H}^+\) ions, contributing to their distinct chemical characteristics.

Basic Solution

A basic solution, also known as an alkaline solution, has a higher concentration of hydroxide ions \( ext{OH}^-\) compared to hydrogen ions \( ext{H}^+\).
Such solutions have a pH greater than 7 on the pH scale.
Bases feel slippery and can taste bitter, such as baking soda and soap.
Basic solutions are known for several properties:

• They turn red litmus paper blue.
• They can conduct electricity in water due to the presence of \( ext{OH}^-\) ions.
• They can neutralize acids during chemical reactions, resulting in water and salt.

The high concentration of hydroxide ions is key to understanding why solutions exhibit basic characteristics.

Neutral Solution

A neutral solution is characterized by a balanced concentration of hydrogen ions \( ext{H}^+\) and hydroxide ions \( ext{OH}^-\).
On the pH scale, a neutral solution holds a precise pH of 7.
The most common example of a neutral solution is pure water, which neither tastes sour nor bitter and doesn't react with indicators like litmus paper.
A neutral solution does not alter the color of litmus paper, and it maintains equilibrium between acid and base properties without exhibiting either specifically.
In scientific terms, neutrality indicates that the molar concentrations of \( ext{H}^+\) and \( ext{OH}^-\) are exactly equal, leading to a stable and non-reactive state in most chemical scenarios.

Hydrogen Ions

Hydrogen ions \( ext{H}^+\) are positively charged ions that play a significant role in defining the acidity of a solution.
When an acid dissolves in water, it releases more hydrogen ions into the solution, increasing its \( ext{H}^+\) concentration, which lowers the pH and makes the solution more acidic.
Understanding hydrogen ions involves recognizing:

• High concentrations of \( ext{H}^+\) lead to a low pH (acidic environment).
• They can attack different materials, making acids corrosive.
• Hydrogen ions can react with hydroxide ions to form water in neutralization reactions.

These ions are fundamental in many chemical processes, especially those occurring in biochemical environments where precise pH control is critical.

Hydroxide Ions

Hydroxide ions \( ext{OH}^-\) are negatively charged ions associated with alkalinity or basicity in solutions.
They result from bases dissolving in water, which increases the concentration of \( ext{OH}^-\) ions, raising the pH and making the solution basic.
The roles played by hydroxide ions include:

• Decreasing \( ext{H}^+\) concentration by reacting with them, which leads to a basic environment.
• Contributing to the slippery feel of basic solutions, like soapy water.
• Neutralizing acidic solutions by forming water and reaching equilibrium.

Hydroxide ions are crucial in various chemical and industrial applications where controlling the pH is necessary for desired reactions and processes.