Question

Which of the following describes substances with a low pH? A) neutral C) dense B) acidic D) basic

Short answer

Substances with a low pH are acidic (Option B).

Step-by-step solution

Understand pH Scale

The pH scale is a measure of how acidic or basic a substance is, ranging from 0 to 14. A pH less than 7 indicates an acidic substance, a pH of 7 is neutral, and a pH greater than 7 indicates a basic substance.

Identify Properties of Low pH

A substance with a low pH has a pH value that is less than 7. These substances are categorized as acidic.

Compare Options with Low pH Characteristics

Review the options provided in the exercise: - Option A (neutral) describes a substance with a pH of 7. - Option B (acidic) describes a substance with a pH less than 7. - Option C (dense) is unrelated to pH characteristics. - Option D (basic) describes a substance with a pH greater than 7.

Determine Correct Option

Since a low pH corresponds to acidic characteristics, Option B ('acidic') is the correct description of substances with a low pH.

Key concepts

Acidic Substances

Substances with a low pH are known as acidic substances. They have a pH value that is less than 7 on the pH scale, which is a numerical representation of acidity and basicity. This means they have a high concentration of hydrogen ions (H⁺) and can produce a sour taste, similar to lemons or vinegar. Some key properties of acidic substances include their ability to react with metals to produce hydrogen gas and their ability to turn blue litmus paper red.
It's important to remember that acids can be strong or weak, depending on how completely they dissociate into ions in water. Strong acids, like hydrochloric acid, dissociate fully, releasing more hydrogen ions and lowering the pH significantly. On the other hand, weak acids, such as acetic acid found in vinegar, do not completely dissociate, resulting in a higher pH compared to strong acids.

• Low pH (less than 7)
• High concentration of H⁺ ions
• Turns blue litmus paper red
• Can taste sour

Neutral pH

The term 'neutral pH' refers to a pH value of exactly 7. This value is considered neutral because it indicates a balance between acidic and basic properties. Water is a classic example of a neutral substance, as it has a pH of 7.
Neutral solutions have an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻), meaning they are balanced in terms of acidity and basicity. These solutions do not change the color of litmus paper, which makes them particularly useful in laboratory settings where a base level of neutrality is needed. Neutral substances play an essential role in various applications, including biological systems where maintaining a balanced pH is crucial for enzymatic activities and metabolic processes. This balance ensures that biological functions proceed correctly and efficiently.

• pH of exactly 7
• Equal concentrations of H⁺ and OH⁻
• Does not change litmus paper color

Basic Substances

Basic substances are those with a pH greater than 7. Also known as alkaline substances, they have a lower concentration of hydrogen ions (H⁺) and a higher concentration of hydroxide ions (OH⁻). Basic substances often feel slippery to the touch and can turn red litmus paper blue. Common examples include household cleaning agents like bleach and baking soda.
This characteristic is due to their chemical properties, which allow them to accept hydrogen ions or donate a pair of electrons in reactions. Basic substances can be either strong or weak, much like acids. Strong bases, such as sodium hydroxide, dissociate completely in water, providing a high concentration of OH⁻ ions and a higher pH. Weak bases, like ammonia, do not fully dissociate, resulting in a pH closer to neutral.

• pH greater than 7
• High concentration of OH⁻ ions
• Turns red litmus paper blue
• May taste bitter and feel slippery