1.1.2 Control Variables

Identifying Control Variables

In an experiment, a variable is any factor that could change or be changed
There are different types of variables within an experiment
- The independent variable: the only variable that should be changed throughout an experiment
- The controlled variables: any other variables that may affect the results of the experiment that need to be controlled or monitored
- The dependent variable: the variable that is measured to determine the outcome of an experiment (the results)

It is essential that any variable that may affect the outcome of an experiment is controlled in order for the results to be valid
Preliminary research and preliminary studies can be used to identify variables within an experiment and to determine ways of controlling these variables effectively
The science surrounding the issue / problem being investigated is likely to contain information about different factors or variables that may exist

There are several experiments that can be carried out to investigate the properties of ideal gases
Factors that can be changed include:
- Temperature
- Pressure
- Volume
- Number of moles of gas

The key point with ideal gas experiments is to ensure that only one of these variables is changed during a particular experiment
- This is known as the independent variable
All other variables must be controlled (they must stay the same)
- These are known as the control variables
When investigating Charles’ law:
- The temperature is varied (independent variable)
- The volume is measured (dependent variable)
- The pressure and number of moles must be kept the same (control variables)
When investigating Boyle’s law
- The pressure is varied (independent variable)
- The volume is measured (dependent variable)
- The temperature and number of moles must be kept the same (control variables)
If these control variables are not kept constant, they could affect the results of the experiment
- This would make the results unreliable