Working scientifically: reaction-rate investigations

Independent variable

the factor you deliberately change, such as temperature or concentration

Dependent variable

what you measure, such as time taken or gas produced per minute

Controlled variables

factors kept the same, such as reactant volume, mass, particle size, equipment and procedure

Why control variables?

So you can judge whether the independent variable caused the change in results

Testable hypothesis

predict how changing the independent variable will affect the dependent variable, and explain why

E.g If acid concentration increases, the reaction rate will increase because more acid particles per volume will cause more frequent collisions

Fair test

change one independent variable, measure the dependent variable consistently, and keep other relevant variables constant

Measuring rate

measure gas volume produced over time, mass lost over time, or time taken to reach a clearly defined endpoint

Safety

wear eye protection; handle acids and hot equipment carefully; use a suitable method to collect gas; follow teacher instructions

Possible errors

inconsistent timing or mixing, leaks, inaccurate measurements, temperature changes, or judging an endpoint by eye

Improvements

repeat trials and calculate a mean; use more precise equipment; keep temperature controlled; seal apparatus properly; use a consistent endpoint