Variables in chemistry investigations

Rule and key idea

Independent variable: what the investigator deliberately changes. Dependent variable: what is measured in response. Controlled variables: what is kept the same so the test is fair.

change one variable · measure one variable · keep the rest the same

Worked examples

Try two questions

1. Investigation: Salt is stirred into water at different stirring speeds, using 5 g of salt each time, and the time to dissolve is recorded. In this investigation, which is the independent variable?

   1. the mass of salt
   2. the stirring speed
   3. the time to dissolve

2. Investigation: A whole antacid tablet and a crushed antacid tablet of equal mass are each dropped into the same volume of room-temperature water, and the time until the fizzing stops is recorded. In this investigation, which is a controlled variable?

   1. the time until the fizzing stops
   2. the volume of water
   3. whether the tablet is whole or crushed (surface area)

Answers and reasoning