### E21b. Sig Figs

Posted:

**Wed Oct 02, 2019 12:10 am**If the given number is 25.92 mg of HF why is the amount of significant figures for the answer 3?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=9&t=45893

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Posted: **Wed Oct 02, 2019 12:10 am**

If the given number is 25.92 mg of HF why is the amount of significant figures for the answer 3?

Posted: **Wed Oct 02, 2019 1:09 am**

I'm also confused by this, but it may have to do with the work that's done for the problem? so when you divide the 25.92 x 10^-3 by 20.01 mol and get 1.30 x 10^-3 the answer for this part (1.30 x 10^-3) has 3 sig figs, which is the least amount of sig figs in part, so this might be why the final answer for b is 3 sig figs.

Posted: **Wed Oct 02, 2019 7:54 am**

I can't seem to find the problem, but the amount of sig figs is determined by the sig figs of the amount given (by the given amount with the least sig figs), so although you may get a number with less sig figs when you do your calculations you should refer back to the given amounts. So maybe the book was mistaken if it didn't give the amount of sig figs as the given amount with the least amount of sig figs. I hope this helps!

Posted: **Wed Oct 02, 2019 4:20 pm**

This was also confusing, but it may be possible that when calculating the molar mass of HF, you use 1.01 as the molar mass for hydrogen which is given in 3 significant figures so the book would like to keep using 3 significant figures.

Posted: **Wed Oct 02, 2019 4:22 pm**

it depends on the number of sig figs used for when you calculate molar mass.

Posted: **Wed Oct 02, 2019 4:26 pm**

I agree with the above answers; it must have something to do with the molar mass calculations.