Question

Chemicals can be classified as acidic, neutral, or basic, depending on their \(\mathrm{pH}\) measurements. \(\mathrm{A} \mathrm{pH}\) below 7 indicates that a substance is acidic, a \(\mathrm{pH}\) of 7 means that a substance is neutral, and a pH above 7 means that a substance is basic. An indicator is a chemical compound that, when added to a substance, changes color based on the \(\mathrm{pH}\) of the solution. For example, cabbage juice is an indicator that turns blue when added to a basic substance. $$ \begin{array}{|l|l|} \hline \text { Liquid } & \text { pH } \\ \hline \text { apple juice } & 3 \\ \hline \text { water } & 7 \\ \hline \text { acid rain } & 5 \\ \hline \text { ammonia } & 11 \\ \hline \end{array} $$ Based on the information and the table above, which of the following substances, if combined with cabbage juice, would cause the cabbage juice to turn blue? A. apple juice and acid rain B. water C. acid rain D. ammonia

Short answer

The correct answer is D. Ammonia, as it is the only basic substance in the table with a pH value above 7, which would cause the cabbage juice to turn blue.

Step-by-step solution

Identify basic substances

Based on the pH values provided in the table, we can label each substance as acidic, neutral, or basic: - Apple juice: pH 3, acidic - Water: pH 7, neutral - Acid rain: pH 5, acidic - Ammonia: pH 11, basic

Select the substance that will turn cabbage juice blue

As mentioned in the exercise, cabbage juice will turn blue when added to a basic substance. Based on our classification in Step 1, the only basic substance in the table is ammonia. Therefore, the correct answer is D. Ammonia.

Key concepts

Acids and Bases

Acids and bases are two important groups of chemicals that have distinct properties and play crucial roles in various chemical processes. Understanding them is essential to grasping the basics of chemistry.
Acids are substances that donate protons (or hydrogen ions, H⁺) when dissolved in water. They usually have a sour taste, can dissolve metals, and turn blue litmus paper red. Common examples include lemon juice, vinegar, and hydrochloric acid.
Bases, on the other hand, are substances that accept protons or release hydroxide ions (OH⁻) in a solution. They tend to have a bitter taste, feel slippery to touch, and turn red litmus paper blue. Examples include baking soda, bleach, and ammonia.
The interaction between acids and bases is called neutralization, which often results in the formation of water and a salt. This balance between acids and bases is measured using the pH scale, making it essential to classify substances properly.

Chemical Indicators

Chemical indicators are substances that signify the presence, absence, or concentration of an analyte by changing color. They are highly useful tools in chemistry, especially when identifying acids and bases.
Indicators are weak acids or bases themselves, and they change color at certain pH levels. This allows them to visually express whether a solution is acidic, neutral, or basic. For example, litmus paper, a common indicator, turns red in acidic solutions and blue in basic ones.
In the exercise, cabbage juice is highlighted as a pH indicator that changes color depending on the solution it is mixed with. It turns blue in basic solutions, allowing visual identification of substances with high pH values. This color change provides a simple way to understand the acidic or basic nature of a substance without complex equipment. Thus, chemical indicators are practical and easily interpretable for both students and chemists alike.

pH Measurement

The pH measurement is a key concept in chemistry used to determine how acidic or basic a solution is. It is a scale that ranges from 0 to 14, with lower numbers indicating increasing acidity and higher numbers indicating increasing basicity. A pH of 7 is considered neutral, which is the pH of pure water.
The pH scale is logarithmic, meaning each whole number change represents a tenfold change in hydrogen ion concentration. For example, a substance with a pH of 3 is ten times more acidic than one with a pH of 4.
Accurate pH measurement is crucial in many scientific and industrial processes. It helps in maintaining the proper pH of our blood, growing plants at optimal pH levels in agriculture, and even in small-scale applications like testing the pH of pool water.
In the exercise, common household liquids are measured by their pH values, which helps in categorizing them as acidic, neutral, or basic. Learning how to measure and interpret pH values effectively allows students to understand the chemical nature of everyday substances.