Source: Extra Practice
When you add a spoonful of baking soda to lemon juice, you observe bubbles of gas being produced. Identify the type of change occurring and explain why.
Model Answer
When baking soda (sodium bicarbonate) is added to lemon juice (which contains citric acid), a chemical change occurs. This is evident because bubbles of gas are produced, which indicates the formation of a new substance. The gas produced is carbon dioxide. Additionally, water and sodium citrate, which are also new substances, are formed. These new substances have properties entirely different from the original baking soda and lemon juice. Since new substances are formed and the change is irreversible, it is classified as a chemical change.
Explanation
Key points for grading:
- Correctly identifies it as a chemical change.
- Explanation based on the formation of new substances.
- Specific mention of gas (carbon dioxide) as evidence.
- Mention of irreversibility.