Question

What is the difference between an acid and a base? What is the pH scale?

Short answer

Acids donate protons and bases accept protons. The pH scale, ranging from 0 to 14, is used to measure how acidic or basic a solution is. A pH less than 7 is acidic, greater than 7 is basic, and 7 is neutral.

Step-by-step solution

Understand Acids

Acids are substances that can donate a proton or accept an electron pair in reactions. They often have a sour taste and can turn blue litmus paper red. Common examples of acids are hydrochloric acid, sulfuric acid and citric acid.

Understand Bases

Bases, on the other hand, are substances that can accept a proton or donate an electron pair in reactions. They can taste bitter and can turn red litmus paper blue. Sodium hydroxide and ammonia are common examples of bases.

Understand pH Scale

The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It ranges from 0 to 14. Acidic solutions have a pH less than 7, basic or alkaline solutions have a pH greater than 7, and neutral solutions, like distilled water, have a pH of 7

Key concepts

Acids and Bases

Acids and bases are two fundamental types of chemicals in chemistry, defined by their behavior in reactions.
Acids are substances that can donate a proton (\( H^+ \)) or accept an electron pair. They often have a sour taste. An easy way to identify them is by their ability to change the color of blue litmus paper to red. Familiar examples include hydrochloric acid (\( HCl \)), sulfuric acid (\( H_2SO_4 \)), and acetic acid (\( CH_3COOH \)).
Bases, in contrast, are substances that can accept a proton or donate an electron pair during a chemical reaction. These substances tend to feel slippery and often taste bitter. A simple test for bases is their ability to turn red litmus paper blue. Common examples are sodium hydroxide (\( NaOH \)) and ammonia (\( NH_3 \)).

• Acids: Donate protons, accept electrons, sour, turn blue litmus red.
• Bases: Accept protons, donate electrons, bitter, turn red litmus blue.

pH Scale

The pH scale is a crucial tool in chemistry used to measure the acidity or alkalinity of a solution. The scale ranges from 0 to 14 and is logarithmic, meaning each whole number change on the scale represents a tenfold change in hydrogen ion concentration. The scale provides important insights into the chemical nature of a solution:

• Solutions with a pH less than 7 are considered acidic. This means they have a higher concentration of hydrogen ions (\( H^+ \)) than hydroxide ions (\( OH^- \)).
• Solutions with a pH greater than 7 are termed alkaline or basic, indicating a higher concentration of hydroxide ions than hydrogen ions.
• A pH of exactly 7 is neutral, typical of pure water, where the concentrations of hydrogen and hydroxide ions are equal.

Understanding the pH is crucial since it affects chemical reactions, biological processes, and environmental systems. Always remember, a solution's pH can influence many properties, including solubility and reactivity.

Litmus Test

The litmus test is a simple, yet powerful method to determine whether a substance is acidic or basic. This test uses litmus paper, which contains a water-soluble dye, to visually demonstrate the acidic or basic nature of a solution.

How It Works

When blue litmus paper is exposed to an acidic solution, it will turn red, indicating the presence of an acid. Conversely, red litmus paper will turn blue when it comes into contact with a basic (or alkaline) solution. This straightforward color change is due to the chemical interaction between the solution's pH and the dye in the litmus paper.

When to Use Litmus Test

While the litmus test is excellent for fast, initial assessments, it does not provide specific pH values. Instead, it simply shows whether a substance is acidic, neutral, or basic.
For more precise measurements of pH, other methods like pH meters or universal indicator solutions may be used. Nevertheless, the litmus test remains a highly useful, quick diagnostic tool in various scientific fields, as well as educational settings, due to its simplicity and ease of use.