B. CIE Preparation - Focusing on Paper 3 (Advanced Practical Skills)
C. CIE Preparation - Focusing on Paper 3, on Salt Analysis and Enthalpy
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Presentation coverage
A. Practical knowledge and understanding
Errors
Accuracy
Titrations
Temperature
Conversions
Graphs and tables
B. Practical skills I
Measuring a quantity
Thermal experiments
How to collect CO2
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CIE Preparation - Paper 3
AS/A-Level Chemistry
23 April 2024
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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.
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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.
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1 - ERRORS
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2 - ACCURACY
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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.
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3 - TITRATIONS
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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.
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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.
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3 - TITRATIONS
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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.
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5 - CONVERSIONS
1000 cm³ = 1 dm³ = 0.001 m³
°C = 273 𝐾
1 cm³ 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 = 1𝑔
1 kJ = 1000 J
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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 figuresconsistent in values in a table.
Make only one table of results for each question.
Circleanomalous results and exclude themfrom 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.
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CIE Preparation - Paper 3
AS/A-Level Chemistry
23 April 2024
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1 - MEASURING A QUANTITY
Repeat and average values.
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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.
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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.