Practical & Investigative Skills

Apparatus
1. Burette
2. Glass Pippette
3. Condenser
4. Gas Syringe
5. Funnel
6. Beaker
7. Round-bottomed Flask
8. Conical Flask
9. Dropping Funnel
Hazard Symbols
1. Highly Flammable
2. Toxic
3. Corrosive
4. Harmful
5. Irritant
6. Oxidising Agent
Separation Techniques
1. Filtration
  1. - Separates insoluble solid from a solid/liquid
  2. - Residue remains on filter paper
  3. - Filtrate runs through the filter paper
2. Distillation
  1. - Separates the solvent from a solution
  2. - Can be used to determine the BP
  3. - Pure water can be obtained from seawater
3. Fractional Distillation
  1. - Separates immiscible liquids
  2. - Substance with lowest boiling point is collected first
4. Separating Funnel
  1. - Separates immiscible liquids
  2. - The liquid with the greatest density separates out as the lower layer
5. Magnetism
  1. - Iron, Nickel and Cobalt are attracted to magnets
6. Crystallisation
  1. - Used to remove small quantities of an impurity from a solid
    1. 1. The impure sample is dissolved in a minimum volume of hot solvent
    2. 2. As the solution slowly cools, the saturated substance crystallises out
    3. 3. The mixture is then filtered and the crystals washed with a small amount of cold solvent
    4. 4. The crystals can be dried out between two filter papers or placed in a warm oven
7. Paper Chromatography
  1. - Separates mixes of different substances e.g. dyes
  2. METHOD
    1. 1. Small spots of coloured substances are placed in a line near the base of the paper
    2. 2. The paper is placed vertically into a beaker or tank contaning a small volume of a suitable solvent
    3. 3. The solvent is absorbed and rises up the paper
    4. 4. The coloured chemicals in the spots dissolve in the solvent and are carried up the paper
    5. 5. The resulting chromatogram is dried and analysed
  3. - The greater the solubility of a compound in the solvent, the greater the distance it will travel up the paper
  4. This technique can be used to...
    1. - Detect whether a coloured dye is a pure compound or a mixture of pigments
      1. A pure compound will produce a single spot on the chromatogram
    2. Indentify a compound/substance by comparison to a known sample
      1. The unknown and known compound will produce the same coloured spot at the same height on the chromatogram
An Investigation
1. Planning
  1. Aim
    1. What is the investigation trying to find out?
  2. Safety
    1. A lab coat and safety glasses must be worn for all practical work
    2. You need to consider specific hazards such as...
      1. Toxic gases - work in a fume cupboard
      2. Corrosive chemicals - wear gloves
      3. Flammable organic compounds - do not heat with a Bunsen burner, use a water bath
  3. Preliminary work
    1. Trial and error is used to find out which practical method and apparatus will work
    2. One of the reagents must be in EXCESS
    3. One of the reagents LIMITS the reaction
  4. Prediction
    1. A prediction is made using you knowledge and the preliminary work
    2. Your prediction should include...
      1. - a simple statement of the expected results
      2. - the predicted shape of any graph which you will draw
      3. - a quantitative prediction based on the reaction equation, mole ratios or other scientific knowledge
    3. Always support and explain your prediction with scientific knowledge
  5. Fair test
    1. Variables make and experiment Valid
      1. Only one variable can be changed
        Independent Variable
        This is the condition that you decide to change
        Dependent Variable
        This is the variable that you measure as a consequence of the changes in the independent variable
        Controlled Variable
        These are the conditions that need to be kept constant to make the experiment a fair test
        keep the temperature the same
        keep the volume the same
        keep the same atmosphere
  6. Method
    1. Give a detailed step-by-step method of the experiment, such that another person could carry out the investigation without further help
  7. Obtaining sufficient, reliable and accurate
    1. Five is the minimum number of variations of the factor under investigation
    2. Reliability of data
      1. If the repeated results for an experiment are the same or very similar, they are said to be reliable
      2. Anomalous results
        - A result which is significantly different from the rest, in a set of results from an experiment repeated several times
        - Results that do not follow the pattern formed by the other results/points on a graph or in a table
        Anomalous results must be clearly identified and not used when calculating averages or drawing lines of best fit on graphs
    3. Accuracy : Is the result obtained correct?
      1. Accuracy is increased by using the correct measuring Apparatus for the task
      2. All apparatus possess inherent errors
2. Obtaining (and recording) the evidence
  1. Results should be displayed in a table
    1. The independent variable must be in the left column
    2. Use clear, accurate headings, which include units
    3. Use SI units
    4. Record all the readings to the appropriate level of accuracy
    5. Record all the readings to the same number of decimal places
  2. Calculations
    1. An average value is usually calculated - DO NOT include anomalous
    2. In rate investigations use - rate of reaction = 1/time
3. Analysis
  1. Graphs
    1. - Use a sensible scale which uses as much of the graph paper as possible
    2. - The independent variable goes on the x-axis and the dependent variable goes y-axis
    3. - Use small crosses to mark the points
    4. - Label the axes carefully and give the units
    5. - Always add a title, indicating what the graph shows
    6. - Circle (and label) any anomalous results
    7. - Draw a line or curve of best fit (do not join up the points)
  2. Conclusion
    1. - State simply what the table of results and graph show
    2. - Use scientific knowledge to explain what you have found out
    3. - Refer to your prediction
4. Evaluation
  1. An evaluation should comment on how well the investigation went and address...
    1. Reliability of the procedure and evidence
      1. - How close together are your results? Are your results reliable?
      2. - Identify and try to explain what caused any anomalous results
      3. - Were there any problems with the procedure?
      4. - Do you have sufficient evidence to support or disprove your prediction?
    2. Accuracy
      1. How close to the real figure are your results? (not always possible to answer)
    3. Inprovements
      1. Reliability
        Can be improved by doing more repeats and only using results which are very similar
      2. Accuracy
        Can be improved by changing the method or equipment used
      3. Limitations
        What are the flaws in the practical method and how could it be improved?
        Always give a reason with your suggestion
      4. Validity
        Assess the above factors and decide how they have affected your results and hence your conclusion. Is your conclusion valid?
    4. Further work
      1. Further work is carried out to obtain more evidence to support the conclusion made in your investigation
      2. It could involve
        - Changing one or more reactants and using same method
        - Using different method/apparatus
        - Obtaining a wider range of results

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