SIg figs and temperature conversion?

Question

I need to know 4.2K in fahrenheit to the proper sig figs. I know that you can do this 1.8 * (4.2 - 273.15) + 32 = -452.11, but I'm not sure how to do it with sig figs. Please help me, 10 points for the first best answer.

Answer 1

4.2 - 273.15 = -268.95 but you round off at the tenths place because of the 4.2, so it's -269.0.  then multiply by 1.8 and it's -484.1.  You might think you go to 2 significant figures but the 1.8 is an exact number (9/5).  Also when you add the 32 that's an exact number too.  So your answer is -452.1.

Answer 2

since you subtract first you ended up with 1 decimal place (4 sig. Figs)

1.8(269.0)+32

the other number are exact (so they are not use to determine sig. figs)

your answer should have 4 sig figs. You should use more decimal places for the 1.8 and 32.

Kent

www.kentchemistry.com