Science (086) — AI-generated practice question

Chemical Reaction: A chemical reaction is a process in which new substances with new properties are formed due to the breaking and making of bonds between atoms. Whenever a chemical change occurs, a chemical reaction has taken place.

Evidence 1 – Evolution of a Gas (Activity 1.3):
Take a few zinc granules in a conical flask. Add dilute sulphuric acid. Bubbles of hydrogen gas are observed around the zinc granules, indicating a chemical reaction has occurred.

$$\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\uparrow$$

Evidence 2 – Change in Colour (Activity 1.2):
Take lead nitrate solution in a test tube. Add potassium iodide solution. A bright yellow precipitate of lead iodide is immediately formed, showing a change in colour.

$$\text{Pb(NO}_3)_2 + 2\text{KI} \rightarrow \text{PbI}_2 + 2\text{KNO}_3$$

Source: Chapter 1, Chemical Reactions and Equations, Section 1.1 and Activities 1.2 & 1.3

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• Definition (1 mark): State that new substances are formed; mention breaking and making of bonds.
• Activity for gas evolution (2 marks): Describe the zinc + acid activity clearly; write the balanced equation with ↑ for gas.
• Activity for colour change (2 marks): Describe the lead nitrate + potassium iodide activity; write the balanced equation. The yellow precipitate of PbI₂ is the key observation.
• Examiners award marks for: correct activity description, correct observation, and correctly balanced equations. Always balance equations — an unbalanced equation loses a mark.