Unit 3 Questions

[Rosie]

If I had a question where I had to provide answer in 3 sig. figures, can you write it either way:
e.g. 5.09 * 10^-2mol  or  0.0509mol

Also, in the question(and for every question):
In order to determine the percentage, by mass, of water in an 850g can of soup, a student heats a 50.28g sample to dryness. After a number of heatings the mass of the residue on two successive weighings is 22.57g.
(a) Determine the percentage, by mass, of water in the soup.
When the answer is given, are you supposed to state your answer to 4 sig. figs not 3 because you are not using the 850g to get the answer for this question. So, does that mean only data you have used or manipulated to get your answer

[Mao]

If I had a question where I had to provide answer in 3 sig. figures, can you write it either way:
e.g. 5.09 * 10^-2mol  or  0.0509mol

both mean the same thing, so yes.

Also, in the question(and for every question):
In order to determine the percentage, by mass, of water in an 850g can of soup, a student heats a 50.28g sample to dryness. After a number of heatings the mass of the residue on two successive weighings is 22.57g.
(a) Determine the percentage, by mass, of water in the soup.
When the answer is given, are you supposed to state your answer to 4 sig. figs not 3 because you are not using the 850g to get the answer for this question. So, does that mean only data you have used or manipulated to get your answer

significant figures are there to indicate *accuracy*, i.e. a less accurate number * more accurate number = not very accurate

if all of the number you have worked with are accurate to four significant figures, then your answer is accurate to four significant figures
hence for this part you should retain four significant figures

it is likely that the second part asks you for the total amount in the 850g can, in which case you can only retain three significant figures

[Rosie]

Thanks for that..