Dependent or independent variable?

Question

okay, so I'm kinda confused again with what my friend corrected me on. Well, for our science report that we're doing, one of the discussion questions involves graphing our results. it is basically on how the reaction rate is affected due to the concentration. and the question tells you to plot a graph of 1/time (ie the measure of reaction rate in time per seconds) against sodium thiosulfate concentration.

what confuses me is that my friend told me that 'time' as a variable always goes on the horizontal axis. And from what i understood, the independent variable is the one that goes on the horizontal axis because it's the one that we change in the experiment. And that the dependent variable (which is the one that you measure) would "depend" on the independent variable itself. So from my experiment, since that the concentration of sodium thiosulfate is the variable which we change in the experiment by diluting, it would makes sense that this is the independent variable. The reaction rate (1/time), however, is the one that we need to calculate, therefore it should be the dependent variable which goes on the vertical axis, because the rate of reaction "depends" on the concentration of sodium sulfate. Right?

so from what i discussed, am i right that the concentration goes on the horizontal axis...or am i wrong, and that the 'time' (reaction rate) should go into the horizontal axis?

i know that it sounds kinda stupid to ask (as im a year 11 and should know all these already), but my friend seems pretty sure thats she's right, while in disagreeing with her. So could someone pls tell us whats the dependent and independent variable in order to clear up our confusion?

Answer 1

i think the time should be on the x-axis

Answer 2

The dependent variable is the one you have to measure, and the one you have no control over. The independent variable is the one controlled by you, and the one that you don't have to measure before the experiment, but you would already know it.

I can see where your friend is coming from: in many experiments, time is controlled. However, here it is not. The time depends on the thiosulphate concentration, so the time variable goes on the y-axis.

Whenever a statement says "Plot A against B", then A goes on the vertical axis and B goes on the horizontal axis.

So yes, you are correct.

Answer 3

You got it right; concentration is your independent variable.

Your friend has the idea of time being the independent variable, most likely from physics (cinematic and dynamic problems) where you study motion; and where time is usually the independent variable; and distance, velocity, position, acceleration, etc. are the dependent variables.

Your friend's understanding is correct but referred only to specific problems; your understanding is more complete; as it applies to all kinds of experiments in general.

Give her the next example:

Plot a graph that shows how the time it takes to build a brick wall changes; if you change the number of workers building the wall.

If you increase the number of workers (independent variable, the one you control); the time it takes to build the wall decreases (dependent variable).

Hope this works for you