CIE Practice 1 - Practical

CIE Preparation - Paper 3
AS/A-Level Chemistry
23 April 2024
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ChemistrySecondary EducationAge 12,13

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CIE Preparation - Paper 3
AS/A-Level Chemistry
23 April 2024

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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 

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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

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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 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.

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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.

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