Improving repeatability and reproducibility
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Modern analytical techniques II
Organic chemistry III
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Explainer Video
Summary
Improving repeatability and reproducibility
In a nutshell
An experiment must be reproducible and repeatable to produce meaningful and scientifically sound data. Reproducibility and repeatability can be increased by following proper technique, this will therefore minimise error.
Repeatability and reproducibility
Repeatability refers to the same person being able to reproduce the same results using the same method and performing the same experiment. Reproducibility refers to a different person doing the same experiment, or using a different method or equipment but still obtaining the same results. For reproducibility and repeatability to be achieved, errors in equipment and technique must be minimised and data must be accurately recorded.
Measuring correctly
Measuring solids
Solids are weighed using a balance, which should be carefully used to ensure accuracy. The scale should be set to zero whilst the container is already on there. If this solid is to be transferred to another apparatus after being measured, it's important to transfer all of the substance carefully.
Measuring liquids
Liquids can be measured with pipettes, burettes and flasks. When measuring liquids it is important to read the apparatus in the following way:
 |
|
apparatus | use |
Pipettes | Pipettes are used to accurately measure a liquid that is being transferred to another container. |
Burettes | Burettes have a tap at the bottom which can be opened and therefore useful for measuring liquids that are being transferred to another piece of equipment in small amounts at a time. |
Volumetric flask | Volumetric flasks come in various sizes and can be used to measure specific volumes of liquid. They can also be used to measure the amount of liquid before another liquid or solid is added to make a solution or they may be used in a dilution. |
Measuring gasses
A gas syringe can be used to withdraw a volume of gas from a closed system. The syringe can be used to measure the amount of gas produced from a system or an experiment.
Measuring temperature
Thermometers or temperature probes are used to measure temperature. The bulb of the apparatus should be completely submerged in the mixture before a reading is taken. The temperature should stabilise before a recording is taken - this usually requires you to wait for a few seconds. Like with measuring liquids, you must read the thermometer at eye level.
Qualitative tests
Tests which produce results that are not numerical data are called qualitative tests. The results can therefore be subjective.
Example
Conducting functional group test-tube reactions in which colour changes are observed in the test tube. These results are therefore more difficult to reproduce. To increase their reproducibility, steps can be taken, such as using a white sheet of paper behind a test tube to see the colour change more clearly.
Synthesising organic compounds
There are techniques which can be used to make organic compounds from other organic compounds. These techniques can also be used to purify the organic compound made.
Technique | Method |
| Reflux | Reflux is based on evaporation and condensation. A mixture is heated in a flask fitted with a condenser. Any material in this flask will evaporate, then condense and drip back into the mixture |
| Distillation | Distillation can be used to separate products in order of increasing boiling points. A mixture is heated and products are collected as they reach their boiling point separately. Distillation can also be carried out after an experiment to purify a mixture. |
| Removing water-soluble impurities | Adding water to a mixture will cause any water-soluble impurities to dissolve. If this mixture is then added to a separating funnel, the organic layer and water-soluble impurities can be easily separated. |
FAQs - Frequently Asked Questions
How is a liquid accurately measured?
When measuring liquids it is important to read at eye-level and from the bottom of the meniscus.
What is reproducibility?
Reproducibility refers to a different person doing the same experiment, or using a different method or equipment but still getting the same results.
What is repeatability?
Repeatability refers to the same person being able to reproduce the same results using the same method and experiment.