Bio and chem HL IA_ controlling variables

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Hi,

i was wondering if you could help me with this.

let's take this as an example:

i want to determine the enthalpy change for the reaction between copper sulphate and zinc. and the lab is a design lab.

what can i write for the variables?

what are the independent variables?

dependent variables?

constants?

can you help me with this? i have some problems with variables.

thanks...

[sweetnsimple786]

Do you know the design of your lab yet? It's hard to figure out the variables separately from figuring out the concept of the design. I used google to find something that fit your experiment, and I got this: http://www.creative-chemistry.org.uk/alevel/module2/documents/N-ch2-11.pdf

I can walk you through the variables, but I don't feel comfortable telling you what they are. It's a skill you'll relish once you've mastered it. =)

So the independent variable is a change that causes another change. This other change is the dependent variable. That's not the best explanation, but I think that you can figure it out. The table is very helpful

And the constants are things that you've seriously kept the same throughout your experiment. If I was dealing with how light affects rate of photosynthesis of a plant, I'd keep the species of the plant the same, the soil it's in the same, the humidity and wind and [relative] temperature the plant experiences the same. Think about constants as if you didn't keep them the same, then you wouldn't be able to figure out if your dependent variable was changing because of one thing or because of another.

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hmmm,

okay, so here what i got after applying what you said:

independent variable: Time.

dependent variable: Temperature.

constants:

- mass of zinc.

- volume of sulphuric acid.

- temperature of surroundings.

is that correct?

can we consider time as dependent variable?

for example if we want to compare it to another experiment, the effect of concentration of HCl on reaction rate say, does it equate the different concentrations of HCl ?

thanks!

[sweetnsimple786]

Yeah, based on that experiment in the PDF, time was the independent and temperature was the dependent.

I was a little surprised because time is usually the dependent variable. I don't exactly understand what you're saying here: "for example if we want to compare it to another experiment, the effect of concentration of HCl on reaction rate say, does it equate the different concentrations of HCl ?"

I don't know what you mean when you say equate. If you're looking at the effect of X on Y, then X will be the independent and Y will be the dependent, as a rule of thumb. Does that help?

By the way, for constants, look at the materials you're using. Same materials can count as constants, too.

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okay, i think i got it now.

and yes, that was helpful. thanks