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Significant Digits in Lab

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I'm doing a lab and I'm a bit confused by the significant digits in the final processed data. For example, suppose I was determining the heat lost by a system and the data in the first trial was:

​

m: 0.500 kg

c: any constant, let's say 0.800

temp. initial: 25.0

temp. final: 21.0​​

​​

Q = (0.500) * (0.800) * (25.0-21.0)

Q = (0.500) * (0.800) * (4.0)

Q = 1.6

​​

My final answer has 2 significant figures according to the calculation shown above but, my raw data all had 3 significant figures. I've heard people say that keep the same amount of significant figures as the raw data. So what would I do in this case?​

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You keep # of significant figures for multiplication/division, and place value (typically decimal places) of least significant number for addition/subtraction.
Here when you multiply, the change in temperature is in fact only goes to the tenths digit, or 2 sig figs, so your calculations are correct. 

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I would keep the final answer as 3 SF.

The number of SF in your final answer depends on the precision of your apparatus. 

 

Leave your calculations as this:

Q = (0.500) * (0.800) * (25.0-21.0)

Then you can give your final answer to 3 SF.

Edited by Msj Chem

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