SIGNIFICANT FIGURES again. (1 Viewer)

[wrxsti]

everyone has conflicting views... could someone please finally clear this up...
last time i did this thread i got more confused :S
like for example.. determine the (H+)concentration of a solution with a PH of

a) 1.6: 0.03

b) 1.87: 0.013


i am of the idea that for the first one... it would be to 2 decimal places.... whilst the second it would be to 3 decimal places......
is this correct


also.... in titrations if we have 25ML 0.025 Moles/L Acid and 26 ML of base neutrilised it..... the answer would be to 3 decimal places???????
so answer would be 0.024Moles/L

(NOTE will this answer be to 2 significant figures... or 3 decimal places)
and also.... are SIGNIFICAT figures THAT important that we will lose marks over them?

 

[wrxsti]

thats a relief........ im worrying more about significant figures and decimal places then the actual content.... :S

 

[Cara.Mel]

0.03 is only one sig fig, zeros before the first number don't count
It's like if I decided to write one gram as 0.001kg, it's not suddenly any more accurate

 

[wrxsti]

well 0.03 is to 2 decimpal places.... (H+ Concentration) PH of 1.6 is 0.03 to 2 decimal places ... thats pretty much what im asking... PH is to 2 significant figures....so we should give our (H+Conc) to 2 decimal places?

 

[watatank]

surely two decimal places is enough?

also.... in titrations if we have 25ML 0.025 Moles/L Acid and 26 ML of base neutrilised it..... the answer would be to 3 decimal places???????
so answer would be 0.024Moles/L

(NOTE will this answer be to 2 significant figures... or 3 decimal places)
and also.... are SIGNIFICAT figures THAT important that we will lose marks over them?

i'm taking that your calculations are correct...

0.024Moles/L is the answer to 3 d.p.

2.4 * 10^-2 is the same answer, except to two sig fig.

 

[Trebla]

The general rule of thumb is that the number of significant figures that your answer should have should be the same as the figure in the question with the smallest number of significant figures.

Significant figures are to account for accuracy and error ranges. Therefore, the more correct significant figures you have, the more accurate your data should be. This means that the accuracy is limited by the data given in the question which has the smallest number of significant figures. Therefore, your answer is limited to that accuracy level, hence your answer should have just as many significant figures and no more.

For example, if you are given data such as 2.71 and 3.1415 to use, the 2.71 has the lower level of accuracy and precision because it has 3 significant figures which is less than 5 significant figures given by 3.1415. Therefore your answer should be no more than 3 significant figures.

Significant figures are not that important in the HSC. You won't lose marks unless you make a very inappropriate rounding. (e.g. in a titration you shouldn't round 22mL to 20mL for the titre). However, they are important in university science, because accuracy and precision in the real world of science is extremely important to consider when analysing a set of data.

 

[brenton1987]

0.03 is only one sig fig, zeros before the first number don't count
It's like if I decided to write one gram as 0.001kg, it's not suddenly any more accurate

Actually 0.03 has two significant figures. Zeros count before the number if theyre after a decimal place.
0.001 has three significant figures.

 

[Trebla]

0.03 has 1 significant figure, not 2.

0.030 has 2 significant figures.

Zeros before a non-zero digit of a decimal place do not count because they only indicate digit position, not its accuracy. The zeros after a non-zero digit do contribute to significant figures because they contribute to its accuracy and precision.

http://en.wikipedia.org/wiki/Significant_figures

 

[wrxsti]

as stupid as it seems... yes.. (i had the chemistry course memorised a little over 4 months ago )

when i do some CSSA papers and i look in the guildlines (for calculation questions) they say "2 signifcant figures" in bold... so i get freaked thinking that i would get it wrong if i didnt :S

oh. and btw i dont go to a selective school

 

[ssejamafone]

I conclude that: significant figures = fayl

Why can i never wrap my head around these random things that must, of course, be so important???

Trebla = object of worship ^(--_--)^

 

[yoakim]

well 0.03 is to 2 decimpal places.... (H+ Concentration) PH of 1.6 is 0.03 to 2 decimal places ... thats pretty much what im asking... PH is to 2 significant figures....so we should give our (H+Conc) to 2 decimal places?

Yes, you are correct. I understand what you're asking. pH relates to sig figs, and [H+] relates to decimal places. THere are many examples in the CC textbook, and 3 exercises with about 20 questions that will help ya. I kept getting confused, but I repeated each question about 4 times until I got the hang of it.

 

[me121]

I don't think that you will get marked down for having too many sig fig. Just use 3. that is usually enough.