Practicals

• Making salt crystals

  Take a base like copper peroxide and an acid like concentrated sulfuric acid. Heat the acid in a beaker, then add excess copper oxide. Filter out the unreacted copper oxide. Gently heat the solution in an evaporating basin over a beaker of water on a tripod above a Bunsen burner flame to obtain solid crystals of copper sulfate
• Base


  • Something that can neutralize an acid
• Electrolysis


  Causing a chemical reaction using electricity. Put the solution (e.g., sodium chloride solution) in a beaker. Place two carbon electrodes in the solution, ensuring they don't touch. Connect them with crocodile clips and cables to a power supply or battery. The electrode connected to the positive terminal (usually red) is the anode, and the negative (black) is the cathode. Depending on the reactivity of the cation and anion in the solution, different products are formed at the electrodes
• If the cation in solution is more reactive than hydrogen, it will stay in solution and hydrogen will be reduced to make H2 gas. If the positive ion is less reactive than hydrogen, it will be reduced at the cathode. If the anion is a halogen like chlorine, it will be oxidized at the anode to form a gas (e.g., Cl2)
• Proper safety measures include using goggles and gloves when working with chemicals
• Accuracy in measurements can be improved by reducing errors and uncertainties, such as aligning the eye with the measurement to reduce parallax error and taking multiple or repeat measurements to calculate a mean
• Answers can be written in bullet point format for clarity and to help both the student and examiner keep track of the points being made
• Anode oxidation


  Negative ion (anion) is a halogen like chlorine, it will be oxidized at the anode to form a gas (chlorine gas in this case)
• Anode oxidation


  If the anion is not a halogen like chlorine, for example, sodium sulfate, oxygen gas is produced at the anode instead
• Temperature changes during a reaction


  Reaction carried out in a well-insulated polystyrene cup with a thermometer inserted through a lid, maximum temperature recorded as the dependent variable. Increasing volumes of the alkali (independent variable) lead to a decrease in maximum temperature as the same energy is spread through a greater volume of solution
• Rates of reaction - Gas volume measurement


  Gas volume measured every 10 seconds in an inverted measuring cylinder to observe the rate of reaction. Variables like temperature or concentration can be changed to compare multiple reaction curves
• Rates of reaction - Turbidity measurement


  Reaction between sodium sulfate and hydrochloric acid causing turbidity, time taken for a cross drawn on paper to disappear is measured as the dependent variable. Conditions like temperature or concentration can be changed as the independent variable
• Chromatography


  Separation of solutes or particles in a mixture by allowing the solvent to move up the chromatography paper (stationary phase) by capillary action. RF value (retention factor) calculated by dividing the distance the solute moves by the distance the solvent moves
• Water purification - Distillation

  Distillation process used to purify water, leaving behind pure water. Distilled water is considered drinkable if it has low enough levels of salt and microbes
• Water purification

  We distill water to leave pure water, which is considered potable (drinkable) if it has low enough levels of salt and microbes
• Desalination


  Removing salt from water through any method
• Neutralization


  Carrying out a titration to determine the concentration of an acid or alkali by neutralizing them
• Titration

  Using a glass pipet to measure out a specific volume of the alkali, adding an indicator like ethyl orange, filling the buret up to the 0 cm³ mark, and slowly adding the acid drop by drop until neutralization is reached
• For triple, knowledge of flame and precipitate tests is expected to identify metal and non-metal ions, particularly sodium and chloride ions
• Flame test: Dip a piece of nichrome wire in a compound solution or powder and place it in a Bunsen flame to identify metals
• To test for carbonate ions, add hydrochloric acid and check for the formation of carbon dioxide by collecting the gas and putting it in lime water
• To test for halide ions, add nitric acid and barium chloride to identify chloride, bromide, and iodide ions based on the resulting precipitates
• If water is purified well, positive tests for sodium or chloride ions should not be observed