Study Notes
Chemical properties describe a substance's potential to undergo a chemical change, which alters its composition. Acids and alkalis are substances that form ions in water, affecting the pH level of a solution.
- Chemical change — A change that alters the composition of the original matter. Example: Burning wood turns it into ash and gases.
- Acids — Substances that form positively charged hydrogen ions (H+) in water. Example: Hydrochloric acid in the stomach helps digest food.
- Alkalis — Substances that form negative hydroxide ions (OH-) in water. Example: Sodium hydroxide is used to make paper and detergents.
- pH scale — A numerical scale from 0 to 14 indicating how acidic or alkaline a solution is. Example: A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline.
- Indicators — Substances that change color to indicate whether a solution is acidic or alkaline. Example: Litmus turns red in acid and blue in alkali.
Exam Tips
Key Definitions to Remember
- Chemical change
- Acids
- Alkalis
- pH scale
- Indicators
Common Confusions
- Confusing physical change with chemical change
- Misunderstanding the pH scale values
Typical Exam Questions
- Name six acids? Hydrochloric acid, sulfuric acid, nitric acid, acetic acid, citric acid, ascorbic acid
- Give one hazard of using sodium hydroxide, and state how to reduce the risks from this hazard? It can cause burns; wear eye protection and gloves
- Give one property that is typical of acids, and one property that is typical of alkalis? Acids taste sour; alkalis feel soapy
What Examiners Usually Test
- Understanding of chemical vs. physical changes
- Ability to identify acids and alkalis using the pH scale
- Knowledge of safety precautions when handling acids and alkalis