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Chemistry Uncertainties Help please?

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Hey I'm in my first year of HL Chem and I just cant seem to understand uncertainties. Could someone explain them to me please??

 

Thank you soooooooooo much!

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SHOULD THE RESULTS BE ROUNDED IN ONLY IN THE END OF THE CALCULATION OR THROUGHOUT THE ENTIRE CALCULATION?

 

The results should be rounded only in the end of calculation. This is to minimize the rounding error throughout the calculation.

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SHOULD THE RESULTS BE ROUNDED IN ONLY IN THE END OF THE CALCULATION OR THROUGHOUT THE ENTIRE CALCULATION?

 

The results should be rounded only in the end of calculation. This is to minimize the rounding error throughout the calculation.

 

But then how do you know how many significant figures/ decimal places it should be rounded to, if the previous calculations weren't. I mean, if the previous results were like long numbers, wouldn't it be arbitrary to decide how many to consider throughout the rest of the calculation?

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SHOULD THE RESULTS BE ROUNDED IN ONLY IN THE END OF THE CALCULATION OR THROUGHOUT THE ENTIRE CALCULATION?

 

The results should be rounded only in the end of calculation. This is to minimize the rounding error throughout the calculation.

 

But then how do you know how many significant figures/ decimal places it should be rounded to, if the previous calculations weren't. I mean, if the previous results were like long numbers, wouldn't it be arbitrary to decide how many to consider throughout the rest of the calculation?

 

 

Throughout your calculation, it's usually the case that you don't round up your answer, but instead leave the answer as it is in your calculator (i.e. have your calculator to memorize it for you). Your calculator can usually handle 10 to 20 decimal digits; this level of accuracy is good enough to minimize any rounding error. Only in the very end of your calculation (when you yield the final result), then you will round it up to 3 significant figures (because 3 s.f. is the standard that the IB uses)

 

Hope this clears up your confusion :)

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Actually, the number of significant figures depends on the precision of the measuring equipment. For example, if you are measuring time and temperature in an experiment and the time is measured to 5 sig figs and your temperarure 3 sig figs, then your final answer in your calculation should be given to 3 sig figs.

If your least precise measuring equipment can measure to 4 sig figs then the final answer can be given to 4 sig figs.

Basically, the number of sig figs for your final answer is limited by the least precise piece of apparatus that you used.

 

I mean i'm aware that when you add/subtract you consider the Decimal places and when multiplying/dividing you consider the sig figs only, but would this be valid throughout the entire calculation, cause then the final answer would be very off!!

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Let me clarify, I am talking about the number of sig figs in the final answer which shouldn't be more than the least precise apparatus that you used. That's why it's better to use precise apparatus, such as a mass balance that can measure to 4 decimal places.

If you are talking about rounding up, you can leave the rounding up to the final answer, or you can round up as you go. Both methods would be accepted in the internal assessment, as long as you make a note in your lab report as to which method you are using.

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