how many significant figures?

Question

A L of water at 25 C dissolves 0.0404 g O2 when the partial pressure of O2 is 1.00 atm. Whar is the solubility of O2 from air, in which the partial pressure of O2 is 159 mmHg?

All calculations aside, I got it right: 8.5x10^-3 g O2/L
BUT my book says that the answer is 8.45x10^-3 g O2/L

I don't have any review in this book about significant figures but from what I've found on the internet, when you multiply or divide, you use the smallest number in the problem to determine the nimber of significant figures. So when the smallest number is 25, is the answer 8.5..... or 8.45......?

Oh that's right. Thanks. It's been awhile.

Answer 1

Did you use the 25 C in the calculation? If not, then the number of significant figures would be 3 (1.00 atm and 159 mm Hg both have 3 sig figs).

Answer 2

25 C is not 2 sig figs. it si actually 25.000000...0000 it si an exact number because you made it exact and it make it easier.

.0404 has 4 sig figs
1.00 has 3 sig figs
and the pressure 158 has 3 sig figs.

you have to use the least number of sig figs in the answer as are in the question because that is the most accurate you can get with the given info. you can only make you answer as accurate as you information. hope this helps

Answer 3

The temperature is irrelevant, being a human concept (and not figuring into your calculations). The smallest number of significant figures used in your calculations is three, so the answer can be expressed in three significant digits.

Answer 4

If the calculation calls for 2 sig.fig. then the answer is 8.5
If the calculation calls for 3 sig.fig. then the answer is 8.45
However, do NOT confuse sig.fig with Decimal Places. If the answer is 8.45 then it is to 2 decimal places and 3 sig.fig.