[2moles]

Please help me understand this once and for all.

I know the basics of significant figures. But I am a bit uncertain when it comes to a more complex task.

Eg. Physical chemistry.
A balloon is launched from ground level.
T1 = 22.5C, P1=754mmHg, V1=1.00*10^6L
T2=240.0K, P2=76,0mmHg, V2=?
The balloon travels 50km up in the air.

Is P1 = 754mmHg = 100kPa or is it 100,28 during the calculations?
How many sig. fig are the answer of this task suppose to have? Is it two because of the 37km, or can I ignore this information because I don’t use it in my calculations?

I have read guides on the internet, and in my textbook, but I am still a bit uncertain..

[nj_bartel]

Don't round at all during the calculations.  Round only your final answer.

[2moles]

Are u sure about this? Can you claim that you have more accuracy eg. 754mmHg than u actually have?

[Borek]

You don't claim you have more accuracy, you just round ONLY the final answer. If you were tp report intermediates - round them for reporting as well, but don't use rounded values for further calculations. Otherwise your final result will depend on the order of calculations.

So, the result of conversion 754mmHg should be reported as 100 kPa, but 100.28 during calculations. If you don't like the idea of 'using' more digits than you have think about it as of not 100.28, but (754*whatever_conversion_factor_you_use) - expression of not calculated value (yet).

No idea where you got 37 km from (should it be 50?) but - as it is not used in calculations - it doesn't matter.

[2moles]

Ok, got it. Thanks!