Right this thread was made cause student room has this stupid (but necessary) rule about not talking about practical that everyone is scared to give advice. I'm sad because I did an evaluative practical and could have done with a few chemistry common sense pointers.
1.) you can only work in the same units. If the data you are given is in standard conditions then you to must work in the same units. If they have given you kelvin - work in kelvin. If you have been working in ml and they give you values in dmc convert to dmc.
- by the way the difference in temperature for kelvin is the same for degrees so if something changes from 14C to 16C the change in temperature would be the same in kelvin.
2.) you can only work to the lowest degree of accuracy. If you have a pipette that measures to the nearest 0.5 and a weighing scale measures to the nearest 0.05 you can only round your answer to 0.5, i.e. the lowest degree of accuracy.
3.) As a reminder to yourself convert things first before carrying out calculations:
- for example if a reaction gives out heat put a minus sign straight away, and convert to the appropriate units if needed.
- if a reaction takes in heat put a positive sign on it to tell yourself that its endothermic.
-if its in ml and its needed in dmc divide by 1000 straight away, should you forget to do so at the end.
4.) LEARN STANDARD CONDITIONS. To be fair you should know this as it comes up in exams.
5.) know how to convert from a fractions of a mole to a whole mole. This is where I trip up constantly.
6.) learn your formula. Not just the simple AS formulas. If you know your formulas then, you'll know if you get a funny answer. For example if your deducing the structure of something and the question says it has a metal and you get something that exist as a gas at room temp, you're wrong. If you are working out entropy and the reaction is exothermic you should realise that the entropy must be negative because it was spontaneous and didn't require energy. <- this point needs refining.
7.) know more formula, than you need to. You might be asked to calculate percentage error, and how to reduce it. If you know this formula and how to manipulate it then such a question is easy peasey. As well as percentage error you may be asked to compare the degree of accuracy between your answer and the data sheet value.
If you have anymore non-specific tips please share because sometimes its expected that you should know all the above when in actual fact in the midst of an exam, its common to go blank.
By the way mods if you go to the OCR website you'll see in the practical booklet in the resources section I've said nothing they haven't said already, I just said it in plain English in a theoretical context i.e. I haven't actually used my practical for any of the examples given, so please don't delete.
Edit: I'll add the link to the booklet if this thread is still here 2moro cause its late. Plus it's from the gospel of OCR, and a lot more reliable than me.
Guys please don't say what actually came up its not fair to those who choose not to cheat.
OCR A Chemistry GCE evaluative practical tips Watch
- Thread Starter
Last edited by 516359; 10-04-2013 at 20:09. Reason: Title and adding PDF.
- 10-04-2013 03:00