ia Rates of reaction question? Changing moles and concentration?

[abelkoontz]

So i think I did the whole thing wrong

I changed the amount of moles by diluting the solution however I used the same volume of 40 mL (used 40ml for 1 mole, 30ml for 0.75 moles, 20 ml for 0.5 moles etc) but through calculations the concentration stays the same e.g moles/volume = concentration, 1/40 = 0.025, 0.75/30 = 0.025 mol.dm3. So what exactly was my independent variable?? Please help omg 

[kw0573]

Did the volume change concentration of another reactant? The amount and concentration of the catalyst, if any, may also change the rate of reaction.