Temperature Changes in Solutions

This final section explores temperature changes in exothermic reactions and endothermic reactions. The practical aims to investigate how different variables affect energy changes in solutions.

Definition: An exothermic reaction releases energy (heat exits), while an endothermic reaction absorbs energy (gets cold).

The guide focuses on two types of reactions:

1. Displacement reactions (e.g., Copper Sulfate + Iron → Iron Sulfate + Copper)
2. Neutralization reactions (e.g., Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water)

Highlight: Both displacement and neutralization reactions are typically exothermic.

The apparatus setup is described, emphasizing the use of a polystyrene cup for insulation and a thermometer for accurate temperature measurements. The guide explains that the insulation provided by the polystyrene cup reduces the rate of energy transfer to or from the reaction mixture, improving the accuracy of results.

Potential exam questions are listed, covering topics such as:

1. The purpose of using a polystyrene cup and lid
2. Resolution and accuracy of measurements
3. Repeatability, calculating mean results, and uncertainty

Example: Using a polystyrene cup reduces temperature loss to the surroundings, making the results more accurate.

This section provides students with a comprehensive understanding of energy changes in chemical reactions and the practical skills needed to measure and analyze these changes accurately.

Making a Salt from a Carbonate or Oxide

This section covers the process of creating a pure, dry sample of a soluble salt from an insoluble carbonate or oxide. The practical demonstrates the reactions between acids and metal oxides or carbonates to form salts.

Definition: A salt is an ionic substance formed from the reaction between an acid and a base.

The guide explains two main reactions:

1. Acid + metal oxide → metal salt + water
2. Acid + metal carbonate → metal salt + water + carbon dioxide

Highlight: Different acids produce different types of salts: hydrochloric acid makes metal chlorides, sulfuric acid makes metal sulfates, and nitric acid makes metal nitrates.

The apparatus setup is described for both carbonate and metal oxide reactions, including the use of a thistle funnel, delivery tube, and test tubes. The guide emphasizes the importance of heating the solution to ensure complete reaction and filtering to remove excess reactants.

Example: To show that carbon dioxide is produced in the carbonate reaction, limewater (calcium hydroxide) can be used as an indicator.

Potential exam questions are listed, covering topics such as crystallization methods, the purpose of heating and filtering, safety precautions, pH testing, and salt identification.