Chemistry Practical Skills

General Guidelines:


  • Dangerous Chemicals:
    • Bringing dangerous chemicals should be transported by leaving the chemical first in the preparation room, transferring the substance (only the required amount) into a beaker and then transporting it across the room.
    • Chemicals producing fumes should have a glad wrap on top of the beaker and should always stay in the fume cupboard.
    • Acids and base neutralisation can be found in the relevant dot point here:Acid Neutralisation
  • Disposing of Chemicals
    • Some chemicals can be poured down the sink however bromine water and heavy metals such as lead and lead precipitates cannot be poured down the sink. They must first be poured into a heavy metal container and then subsequently disposed of through a third party specialist or other relevant authority.
  • Use of Chemicals
    • Required amount ONLY.
    • Exothermic and reactive reactions must be monitored carefully.
    • Label all tubes.
  • Dangerous Practices:
    • Broken glassware should be disposed of in the 'sharps' bin.
    • Biochemical waste should be disposed of in the 'bio hazardous waste' bin.
    • Gas taps should be turned on, after connecting to the Bunsen burner with a closed air intake, and then subsequent lit.
    • Heat resistant glass and non-heat resistant glass should be separated and care to be taken on their use.
  • Safety Equipment
    • LAB COAT
    • Gloves (where applicable)
    • Minimal exposure (where applicable)
    • Common sense.

Assessing validity reliability and accuracy:

Assessing the validity, reliability and accuracy of an experiment is a simple matter of resolving the experiment in terms of its:

  • Aim
  • Method
  • Results


Validity of an experiment is based on how well the experiment is able to test the aim.
For example the molar heat of combustion of alkanols experiment was set out to find the molar heat of combustion of various alkanols. It failed miserably and thus is not particularly valid. However, the comparative molar heat of combustion of the alkanols allows each alkanol to be compared thus giving validity to the experiment.
In order to improve the experimental validity of any experiment the method must be changed in order for the experiment to thus achieve the aim. Methods may not be able to change due to cost, time or equipment factors thus rendering the experiment invalid.


Reliability is how well the experiment can reproduce its results. An experiment is reliable if the results it gives is particularly consistent. Reliability can thus be increased if the experiment is repeated, conformed, checked with other groups results and their conformed. If the method can also be changed to produce more consistent results that is considered an improvement to reliability as well. The less the results deviate, the higher the reliability of the experiment.


Accuracy of the experiment is how well the experiment is able to achieve the ACCEPTED VALUE of the result or how well it is able to obtain accurate data from the observations and produce results that can be compared. Accepted values are values that the scientific community agrees on to be the universal value of the result. However, if the experiment is entirely new with no accepted values until a further experiment can be devised to improve the accuracy, the experiment is deemed accurate and that is the new accepted value for those results. The accuracy of an experiment can be improved by the use of smaller scales, equipment of smaller scales and recording of observations quantitatively.

Interrelations of Accuracy and Reliability:

Accuracy and reliability are subtly linked however it is possible to have an experiment that is not accurate but reliable and vice versa, or both accurate and reliable or neither.

An example of an experiment that is reliable but not accurate is the alkanols experiment. So much heat is lost that it can not be an accurate representation of the molar heat of combustion.

An example of an experiment that is accurate but not reliable is a parabolic motion. Here due to numerous factors though the equipment detects all factors to an accurate degree, reliability of the results is skewed due to air resistance, wind and other factors unforeseen.

Most qualitative experiments are both accurate and reliable as it is very clear the differences between results.
Titration is a quantitative experiment with a high degree of accuracy and reliability.
Anion and cation tests have a high degree of accuracy and reliability.

If it is both not accurate and not reliable, its a bad experiment.