Lab Report Electrochemistry

[meoww]

Thank you Keel

Just one more thing. I'm struggling with the uncontrolled variable and sources of error in this experiment. Also I'm still not sure about whether I should change the concentration of either Copper sulphate or Zinc sulphate or both, because when I did my trials, the result came out as:

Copper Sulphate: 0.1M Zinc Sulphate: 0.1M => emf: 0.98V

Copper Sulphate: 1.0M Zinc Sulphate: 1.0M => emf: 1.05V

Copper Sulphate: 0.1M Zinc Sulphate: 1.0M => emf: 1.00V

Copper Sulphate: 1.0M Zinc Sulphate: 0.1M => emf: 1.00V

Help!

[Keel]

If I'm correct you are doing a design IA yes? If you are then there's no need to worry about what will happen if the experiment is actually done. Just make sure that you have a focused research question, you have listed all your variables (independent, dependent and controlled) and that your method is flawless with a suitable choice of equipment. Here's a link to the Chem IA guide:

If the reply didn't help you, post again and we'll see how we can help you. Good luck!

[meoww]

Yes I'm doing the IA design. I have done 1 so far and this is my 2nd design practical. Although I understand this experiment doesn't have to work, it is likely that I have to include potential errors in my design, so I have to think about the uncontrolled variables. I'm actually not sure about my method either, as I said before, whether to change the concentration of CuSO4, ZnSO4 or both.

Any idea ?

[Keel]

Yes I'm doing the IA design. I have done 1 so far and this is my 2nd design practical. Although I understand this experiment doesn't have to work, it is likely that I have to include potential errors in my design, so I have to think about the uncontrolled variables. I'm actually not sure about my method either, as I said before, whether to change the concentration of CuSO4, ZnSO4 or both.

Any idea ?

No No I never said the experiment doesn't have to work, it DOES have to work, how well it works is another issue. What are your independent variable and the dependent variable? I suspect that you are thinking too much. All you need to do is to think up of a research question. eg. 'How does the increase in the concentration of CuSo4(aq) in a voltaic cell composed of copper and zinc half cells affect the potential difference produced?' Then you just construct the experiment around how you are going to measure that potential difference.

[ibbrasill2010]

I am also doing this experiment (changing concentration of CuSO[4] and ZnSO[4]). I am writing the conclusion but my teacher wants be to comment on the validity of my results and how does voltage change compare to experimental uncertainty. Can anyone please help?!

Thank you so much in advance

[Drake Glau]

She's wanting you to comment on how well your lab design worked in obtaining results. Did you have big uncertainty because of a few steps? Did something not work well at all and you had to improvise? I'm guessing what she means by the voltage change thing is did you data change enough to be significant? If your data reads...1.5+0.5V (that's giant, but you'll get what I mean) and then your next one reads 1.9+0.5V you can't tell if the concentration affected anything because both measurements are within their uncertainties. For all you know the 1.9 could be a fluke (that's what uncertainties are there for) and nothing actually happened. Hope that made sense. Basically if your measurements are all within their own uncertainties then you can tell if anything happened experimentally besides the fact that the world isn't perfect and you had an uncertain result...

[Keel]

I am also doing this experiment (changing concentration of CuSO[4] and ZnSO[4]). I am writing the conclusion but my teacher wants be to comment on the validity of my results and how does voltage change compare to experimental uncertainty. Can anyone please help?!

Thank you so much in advance

What you should be provided with is a literature value for the experiment you have done. This is important because it is an indication of how accurate your experiment was. So the first step is to find out how 'off' your obtained value (the answer reached in your DCP) in comparison with the literature value. This can be done by calculating the % difference:

[(obtained value - lit. value) / (lit. value)] x 100% = % difference in answers

This % now gives an indication of how inaccurate your experiment was. There are now two types of errors or areas of improvement you should consider. The first is improving the equipment that you used in your experiment, thus reducing the effect of random uncertainties; and the second is improving the way the experiment was conducted, or fixing the systematic errors.

You should now comment on which type of error contributed most to this inaccuracy. In your DCP, you should have calculated the total % error due to random uncertainties (ie the +/- ...% at the end of your answer). You can use this to find out what % was caused by systematic errors.

(% diff in answers)% - (total error caused by random uncertainties)% = (total error caused by systematic errors)%

You now have an indication of which error is more responsible for your inaccuracy. It is usually the systematic error. You then state which error is more responsible. You should then proceed to state improvements for both types.

For the first type, random uncertainties, go through all the equipment you've used in the experiment, state the % error they caused and propose an improvement. e.g. 50 cm3 measuring cylinder; +/- 0.5 cm3 caused a 10% error; propose to use a 50 cm3 pipette.

The second type usually requires some imagination and a general understanding of the limitations to the experiment. What systematic errors could have caused inaccuracy? State this systematic error, state which direction it moved your result, state whether it's a minor or major error, and state an improvement. e.g. Heat Loss; Caused obtained value to be higher than actual value; Major error; Use insulative container.

I hope this helps, remember this all comes from a chemist and you should adapt it for your purposes.

P.S. The chemistry forum has some good IA help resources if you need further help:

Also you should check the mark scheme: http://ibchem.com/IB/ibe/IA-2009.htm

Hope this provided some guidance.

[C-Lynch]

I need some help with a practical investigating a factor that affects electrolysis. I am having some trouble with variables. How many do I need? What are some essential ones I should have?

Also, for my method, should I give instructions on how to make the solution or should I preform electrolysis on a premade solution? And lastly: are there any famous examples I could replicate? Imitating one would be infinitly easier.

Thanks

[Drake Glau]

You change one variable for any lab, always. Electrolysis variables could include ion charge of the solution, the anode and cathode substance, current running through the system, and of course temperature.

If you make a solution you need to explain how to make it (explain if you dissolved something, how much solid in how much water, if you are diluting explain how much water needs to be added)

Famous examples are overrated, and usually more complicated (kind of what makes them famous most likely). Just make yourself and simple cell and go with it.

[Alex1307]

I am having some trouble with variables. How many do I need? What are some essential ones I should have?

Don't forget to include a list of all of your controlled variables (the ones that are not supposed to change)and give a brief description of the method you're going to use to control them. For example: temperature, controlled with a thermometer. I know it is kind of obvious, but don't just focus on dependent and independent variables!

I agree with Drake Glau, current, temperature and nature of the electrodes are good variables. You could also change the amount of time, as a longer electrolysis will result in the production of more products. And you can also change the concentration of the solution you're electolyzing. A dilute solution will tend to give out O2 and H2 gas instead of solid metals.