- 藍∮玲Lv 71 十年前最愛解答
Why is fair test so important ?
When you perform an investigation you change the independent variable to find out what the effect of the changes are on the dependent variable.
A fair test is one where you only change one variable at a time.
You are adding magnesium to hydrochloric acid to produce hydrogen and magnesium chloride.
You want to find out what effects the rate of reaction (manefested in the dependent variable as the number of bubbles produced per second).
In a fair test you use a fixed volume of acid, a fixed mass of magnesium and a fixed temperature. You then perform the investigation using different concetrations of acid. You can now state the effect of acid concentration on the rate of reaction.
You can now repeat the experiment by changing another variable and seeing how that effects the rate of reaction.
You now know what effects the rate of reaction most.
In an unfair test you change multiple things or fail to properly control the circumstances.
You perform the same test. You change the concentration of acid, the temperature and the amount of magnesium added.
You find the rate of reaction has increased.
What caused it?
You can't tell because it is an unfair test, you do not know which variable caused the change to the dependent variable.