CIE Practice 1 - Practical

• Chemistry
• Secondary Education
• Age 12,13

CIE Preparation - Paper 3

AS/A-Level Chemistry

23 April 2024

GOALS TODAY

A.     Review exam results

B.     CIE Preparation - Focusing on Paper 3 (Advanced Practical Skills)

C.     CIE Preparation - Focusing on Paper 3,  on Salt Analysis and Enthalpy 

Presentation coverage

A. Practical knowledge and understanding

1. Errors
2. Accuracy
3. Titrations
4. Temperature
5. Conversions
6. Graphs and tables

B. Practical skills I

1. Measuring a quantity
2. Thermal experiments
3. How to collect CO₂

CIE Preparation - Paper 3

AS/A-Level Chemistry

23 April 2024

1 - ERRORS

• Random error - results from the experimenter's inability to take consistent measurements, e.g. in the disappearing cross-experiment

• It is often due to a problem that persists throughout the experiment, such as random fluctuations in room temperature.

1 - ERRORS

• Systematic error - usually caused by measuring incorrectly calibrated or incorrectly used apparatus, e.g. thermometers that consistently read 1°𝐶 above the actual temperature or reading volumes from the wrong part of the meniscus.

1 - ERRORS

2 - ACCURACY

3 - TITRATIONS

• Burette has to be written to 2 DP.
• The two best titres must be within 0.1 𝑐𝑚3 of each other.
• If the first two titres are within 0.1 𝑐𝑚3, then no need for the 3rd titre
• Repeat and find the average titre volume with a spread of not more than 0.20 𝑐𝑚3.

3 - TITRATIONS

3 - TITRATIONS

• Clean all apparatus properly with distilled water before starting the experiments.
• While pipetting, the tip of the pipette should be placed against the wall of the container. This prevents the solvent's droplets from spilling out of the container.
• *Clean the walls with distilled water to ensure you include all moles of solution.
• *Add an indicator as per the instructions. Add too much, and you will get incorrect results.
• Clean the burette and pipette with the solution, but do not use volumetric and conical flasks as they will give inaccurate values.

3 - TITRATIONS

• Always read the bottom meniscus of the burette and ensure the burette does not have any air bubbles to remove the jet space.
• *Tap it to free air bubbles.
• *Open the tap to fill the jet space.
• Always swirl the conical flask.
• *Use a white tile underneath to observe any colour change.
• *Titration ends when any colour change is permanent.
• In your second titration attempt (after the rough titre), adjust the burette tap to dispense drop-wise when the reading is near the end-point to find the exact titre value.

3 - TITRATIONS

4 - TEMPERATURE

• Record to nearest 0. 5°C when thermometer calibrated in 1°C intervals
• Record to nearest 0. 1°C when the thermometer is calibrated in 0. 2°C intervals.
• If one procedure has a greater temperature change, it has higher accuracy due to a lower percentage error.

5 - CONVERSIONS

• 1000 cm³ = 1 dm³ = 0.001 m³ 

• °C  = 273 𝐾

• 1 cm³ 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 = 1𝑔

• 1 kJ = 1000 J

6 - GRAPHS AND TABLES

• When finding a gradient, always use a triangle with a hypotenuse greater than half of the line.
• Label the axis with quantity and unit.
• Plot graph with a fine cross or encircle dots.
• For each heading in a table, write the quantity measured with the unit separated with a slash.
• Keep significant figures consistent in values in a table. 
• Make only one table of results for each question.
• Circle anomalous results and exclude them from calculations.
• The line of best fit drawn should ignore anomalous results.
• Ensure your graph covers more than half the page.
• Points must be within half a small square of the correct position.

CIE Preparation - Paper 3

AS/A-Level Chemistry

23 April 2024

1 - MEASURING A QUANTITY

• Repeat and average values.

2 - THERMAL EXPERIMENTS

• Insulate the container to stop thermal conduction.
• Use a lid to seal the container to stop thermal convection. 
• When heating a hydrated salt, heat to a constant mass.

3 - HOW TO COLLECT CO₂

• Water vapour condenses in the water trough.
• Ensure no air bubbles are in the gas jar when setting up the apparatus.