Significant figures???? (1 Viewer)

[Michaelmoo]

Ok. In general, I've heard that answers in an exam should be given with the same number of significant figures as the value in the data with the least number of significant figures.

Isn't this generally true for the HSC? How picky are they about these details?

But what about an example involving concentration and volume for example. Say the data gives a value for concentration with 4 significant figures; and also gives a value for volume with 2 significant figures.

Now you have to find a second concentration. Wouldn't it be more appropriate to give your answer to 4 sig figures (as this is what they have in the data) or should you stick with 2 sig figures as they say.

Thanks in advance.

 

[zeleboy]

True. If it's a PH reading, to 1 d.p. is best.

 

[Timothy.Siu]

i thought 3 sig figs was the general rule

 

[omniscience]

quote to +infinity significant figures

 

[Woteva636]

We were always taught go to the number of the least accurate data eg if you have the pieces of info, one to three sig figures and two to five, only give your answer to three. do all your calculations with the most acurate data you can (starting with five sig figures then what ever the calculator gives you), then round at the end to three.

the reason: you don't know what the fourth and fifth significant figure in the original data were, therefore you cannot go more accurate than what you were given.

Sorry if you didnt learn anything at all from all that!

 

[Continuum]

I dunno, my teachers are starting to become really picky with this sort of stuff so yeah, it probably is important in the HSC?

 

[kwabon]

suppose if the question gives you a value of 3.214
that has 4 significant figures, then it asks you to do all this crap

and then you get your answer to be 3.21356562395632..........
but the value in the question has 4 significant figures, so you would have to take your answer to 4 decimal places.
so your answer should look like 3.2136

that is the general rule ..... i know, retarded rule, but thats how it is in the HSC.

 

[Trebla]

As long as the rounding is sensible, you will not have any marks deducted. For example, for a titre of 28.53 mL, a rounding of 28.5 mL is more appropriate than say a rounding of 30 mL.

The rules about significant figures outlined above are what real scientists actually follow. If you plan to pursue tertiary science courses, then this rule is definitely important. However, in the HSC they're not too fussed about it...

 

[electrolysis]

We get told to answer to to the max sig figs given in the question...

 

[Michaelmoo]

Ok. So in summary,everyone is saying answers should be rounded off to:

• 1 Decimal Place
• 3 significant figures
• Infinity significant figures
• Most number of significant figures in the data
• Least number of significant figures in the data
• no. of decimal places that is the same no. of significant numbers in the data
• Any sensible amount

I don't know who to follow. The board of studies doesn't specify how many significant figures they want, yet I've heard they penalise for not having the appropriate amount...

Anyone know which one is the best. I think I'll just have to go with the conventional scientific way (5th dot point).

 

[dp624]

sig figs:

ok, when you answer a question
check the number of sig figs they give you in the data.
e.g. 25.0ml of hcl solution was added to 5L of naOh 1.00000Molar solution.

you see here that it's 3,1, and 6 sig figs

your answer will be 'sigfigged' to the least number of sig figs in the data. in this case, 1


@ your initial post:
2 is the way to go

trust me, lol

 

[Pwnage101]

here's my 2 cents:

Least number of significant figures in the data -----> Applies to everything except pH (Note: when they give you the temperature, chemists take kelvin to be the stanard, so even if they give 25Celcius, its taken to be 298 kelvin, and so 3 sig figs


no. of decimal places that is the same no. of significant numbers in the data ---> when calculating pH - this is because pH is a logarithmic scale. eg if ur given [H+] to 3 sig figs,a nd te pH come sout to 1.34859, round to: 1.349.

 

[Michaelmoo]

here's my 2 cents:

Least number of significant figures in the data -----> Applies to everything except pH (Note: when they give you the temperature, chemists take kelvin to be the stanard, so even if they give 25Celcius, its taken to be 298 kelvin, and so 3 sig figs


no. of decimal places that is the same no. of significant numbers in the data ---> when calculating pH - this is because pH is a logarithmic scale. eg if ur given [H+] to 3 sig figs,a nd te pH come sout to 1.34859, round to: 1.349.

R u sure ur talking about the HSC here? Im pretty sure degrees celcius is acceptable.

I might have to check with a HSC marker about the significant figures decimal place thing. First time I've ever heard that.

 

[Fortify]

sig figs:

ok, when you answer a question
check the number of sig figs they give you in the data.
e.g. 25.0ml of hcl solution was added to 5L of naOh 1.00000Molar solution.

you see here that it's 3,1, and 6 sig figs

your answer will be 'sigfigged' to the least number of sig figs in the data. in this case, 1


@ your initial post:
2 is the way to go

trust me, lol

2 is probably your best choice.

 

[Pwnage101]

R u sure ur talking about the HSC here? Im pretty sure degrees celcius is acceptable.

I might have to check with a HSC marker about the significant figures decimal place thing. First time I've ever heard that.

i dont think u understand what i was saying.

Using degrees celcius in HSC is fine (who would use kelvin??) - im just saying that if you have data in the question all to 3 sig fig, but they give you 'the temperature is 25 degrees celcius' - u are not to take that as being 2 sig figs, because its actually 3 sig figs in kelvin form, and thus ur answer to the question would be to the least sig figs = 3 , not 2