Chemistry · Grades 9–12

Measurement & evidence · Quick reference · Grades 9 to 12 · Chemistry

Reference sheet for Grades 9 to 12: variables in chemistry investigations.

Rule and key idea

Variables in chemistry investigations

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

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 a controlled variable? → the mass of salt

Check yourself

Four practice questions on this topic. Try each one before you open the answer.

Investigation: Salt solutions of different concentrations are tested with the same conductivity meter at the same temperature. In this investigation, which is a controlled variable?
- the temperature of the solutions
- the salt concentration
- the conductivity reading
Show the answer
the temperature of the solutions 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.
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 the dependent variable?
- whether the tablet is whole or crushed (surface area)
- the time until the fizzing stops
- the volume of water
Show the answer
the time until the fizzing stops 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.
Investigation: A sugar cube is dropped into 200 mL of water at 10 °C, 25 °C, 40 °C and 55 °C without stirring, and the time to dissolve is recorded. In this investigation, which is a controlled variable?
- the water temperature
- the volume of water
- the time to dissolve
Show the answer
the volume of water 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.
Investigation: Different masses of baking soda are added to 50 mL of vinegar each time, and the volume of gas collected is measured. In this investigation, which is a controlled variable?
- the volume of vinegar
- the mass of baking soda
- the volume of gas collected
Show the answer
the volume of vinegar 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.