Sig Figs? (1 Viewer)

[3.1415926535897]

i always hear thet it is necessary to put answers in correct n umber of sig figs but am unsure what is the correct number?!


is it the most or least sig figs ion the q....

e.g. i used 25.0ml 0.1M HCl , 1.365g NaOH

if there was a q atatched would the answer be in 4 sigfigs or 1?

 

[Slidey]

I'm not sure, but I believe it is least, since you don't want to pretend there is accuracy there that doesn't exist.

 

[3.1415926535897]

is it cos by using most sig figs u assume that say 0.1 is 0.100

 

[BlackJack]

Most is definitely not the answer.
Least is usually the correct answer, but you should think about it before scrubbing everything out.
For your example above, a "0.1M HCl" is probably more accurate than that 1 sig. fig., as it is usually made up carefully. Professionally speaking, the bottle it comes from should say how accurate it is. In that cases of not sure-ness I'd put in 3 if it was something like a titration experiment (there's no point in doing the experiment otherwise with such inaccurate acids!) since the 25.0 ml comes next.
If not then 1. (Although it is quite stupid an aswer.) For pracs that involve these absurd "inaccuracies" you should ask yuour teacher how accurate that 0.1M acid actually is.

is it cos by using most sig figs u assume that say 0.1 is 0.100

Yep. Saying 0.1 is like saying 0.1 +- ~0.05, and etc.

 

[3.1415926535897]

thanks,

dudes

 

[mitochondria]

Strictly speaking, the number of significant figures you use in your final answer should have at most the number of significant figures in the least accurate measurement. i.e. using the example you have given us:

25.0ml (3 sig. fig.) 0.1M HCl (1 sig. fig.) , 1.365g NaOH (4 sig. fig.)

You should only have 1 significant figure in your final answer..

Moreover, you should make no assumptions about any given quantities, i.e. 0.1M HCl IS 0.1M HCl but anything.. Yes, there is certainly uncertainty in the molarity of HCl and it may not be exactly 0.1M (in fact you can never, at least not with our current technology, get an EXACT answer unless you can count the molecules one by one) It follows that saying 0.1M is NOT equal to saying 0.1M +/- 0.05, given that you don't know nothing about how the solution was prepared.. and (i'm not definitely sure about what I'm going to say, but I'll say it anyway) even if you are giving 0.1M +/- 0.05, you will only use 1 sig. fig. in your calculation (some people tend to think that 0.1M +/- 0.05 is 2 sig. fig. which i don't think is the case)

If you are not comfortable with using significant figures and that the question doesn't require you to use it, quote your answer in ndp and put in a bracket next to the answer (to the nearest *an integer* decimal point(s)) Hope that helps