Lesson 8.3: Solutions can be acidic, basic, or neutral

Lesson Focus

Why are some liquids sour and others bitter? This lesson explores the properties of acids and bases, how we measure their strength, and how they interact to form neutral substances like water.

Learning Objectives

• Define acids and bases based on their unique chemical properties and behavior in water.
• Learn to identify if a solution is acidic or basic using indicators and the pH scale.
• Discover what happens when acids and bases mix in a neutralization reaction.

Some substances become acids or bases in water. An acid is a substance that donates a hydrogen ion (H⁺), which is a proton. A base is a substance that accepts a proton, often by releasing a hydroxide ion (OH⁻). This exchange of ions gives them their distinct properties. Which ion makes a solution acidic?

We identify acids and bases by their reactions. Acids react with metals and carbonates and turn litmus paper red. Bases feel slippery because they react with your skin to make soap, and they turn litmus paper blue. These predictable reactions provide safe ways to tell them apart without tasting or touching.

The strength of an acid or base depends on how many ions it releases in water. A strong acid, like HCl, completely breaks apart into ions. A weak acid, like vinegar, only releases a few H⁺ ions. Strength is about the percentage of ionization, not concentration. Why is HCl considered strong?

The pH scale measures the concentration of H⁺ ions. A low pH (0-6) indicates an acid, while a high pH (8-14) indicates a base. A pH of 7 is neutral, like pure water. Each whole number change on the scale represents a tenfold change in acidity. Is a pH of 3 more or less acidic than a pH of 5?

When an acid and a base mix, they undergo neutralization. The H⁺ ion from the acid combines with the OH⁻ ion from the base to form neutral water (H₂O). The remaining ions form a salt. The general reaction is: Acid + Base → Salt + Water. This is how antacids work in your stomach.