Need some science project help please

[DustMolecule]

As some of you may recall, my daughter was doing a greenhouse gas experiment and I had a question about the bromthymol blue indicator solution that I had ordered not being "blue". Thank you all for helping me with that one.

Now I have another question re: same experiment. She's got to list the control, independent variable, and dependent variable and she and I are getting all confused. I THINK

- independent variables are the 5 different gases that she tested

- dependent variable is what happened to the bromthymol blue solution (the color change)

control - is the bromthymol blue solution with no gases bubbled through it

Is THIS right? Also is the "constant" the same as the "control"? If not, what is it?

Any help would be GREATLY appreciated. Thanks for all of your help!

[Ian David]

1. If you want to inject some humor into the project, also test "flatulence"

(stinky)

[DustMolecule]

2. LOL

I don't EVEN wanna think about how one would collect the gas, so let's not go there!

[Ian David]

4. Collect it the same way as sulfur dioxide for stinkbombs

Sort of, anyway...

All you need is a flask, some tubing, and a bathtub.

[DustMolecule]

6. LOL - I didn't really need to know that ......

we've got all the gas we need! Thank you.

[mike_c]

3. that sounds about right...

...without knowing more about what she did. The independent variable is the condition you varied during the experiment. The dependent variable is something that responds to the different independent variables, i.e., you're not changing it directly, but it might change as you vary the independent variable.

A control is generally an experimental treatment that does not receive the same manipulation of the independent variable that the other treatments receive. Its purpose is to make sure that the response you measured (change in the dependent variable) is in fact a response to the independent variable. That's a simple control that covers most situations and I hope it's an accurate description of your control.

[DustMolecule]

5. Thank you mike_c

Then is constant and control the same? OR

Is the test tubes, and balloon gas collectors the CONSTANT and the bromthymol blue that didn't have any gas bubbled through it (like the other 5 test tubes) the CONTROL?

[mike_c]

8. yes, the indicator blue that did not have gas bubbled...

...through it would be considered a control if you treated it just like the ones that did have gas bubbled thru them in every other respect. If that batch of b. blue did not change color, then that tells you that any positive responses you got in your other treatments were not the result of the apparatus, b. blue response to air, experimenter error, bad ju-ju, and so on.

I don't know why your instructions are using the term "constant." We often speak of controls as having the experimental conditions held constant, i.e. all the conditions except the actual treatment (gas bubbling) are kept the same in the control as in the other treatments (same setup, etc), so that's the only reason I can think of for that terminology.

I've got to run to a meeting, so I'll be offline for several hours. Good luck!

[DustMolecule]

9. Thank you again. ...

although the answer was so plainly simple and intuitive...I didn't 'get it' right away. I'm thinking the teacher wanted the students to list all of the constant experimental conditions....as you said "all of the conditions, except the actual treatment" that was the same (sorta weird though, because that's kind of natural/asssumed to list 'what's different only).

Long story (and long night)...I think "we've got it licked! - and finished (thank God)!

Thank you for answering this post sincerely and being most helpful. I was definitely feeling like the 'lost and desperate mom (who's kid thinks/hopes she knows much more than she really does)'.

DU folks are the best!

[DustMolecule]

7. I feel like Dr. McCoy on the old Star Trek Series....

"Dammit Jim, I'm a MOM, not a SCIENTIST"!