significant figures in chemistry answers? (1 Viewer)

[andrewglynn]

how many significant figures should you leave your answers to when answering a problem, and are the hsc markers too strict on this?

 

[madharris]

You leave it to the least number of significant figures in the question e.g.

0.432 of something was mixed with 0.64821 of something and 0.4625 of something also was added fine the something of the solution(Don't you love my question?)

Your final answer should be to 3 sig.fig because of the 0.432
So you would write out your answer as "0.234units (3 sig.fig)

yes the markers are strict on this. you will lose a mark if it's not to the right number of sig figs

 

[someth1ng]

You leave it to the least number of significant figures in the question e.g.

0.432 of something was mixed with 0.64821 of something and 0.4625 of something also was added fine the something of the solution(Don't you love my question?)

Your final answer should be to 3 sig.fig because of the 0.432
So you would write out your answer as "0.234units (3 sig.fig)

yes the markers are strict on this. you will lose a mark if it's not to the right number of sig figs

There's usually only 1-2 marks allocated to correct significant figures.

 

[golgo13]

Generally do it correct to the figures given in the question but if that is not present the magic number is 4 from memory

 

[Demise]

And always remember, if a question has 2 components (or more), and you had to find the value of something in the 1st component, write out the answer to as many D.P as they ask for (or 4), but keep the full answer in your calculator if it ends up to be like 4.2846394745839 - Write it as 4.2846, but save the previous answer and use it for component B.

 

[deswa1]

There's usually only 1-2 marks allocated to correct significant figures.

This. They don't mark every question on sig figs- they pick a question(s) and mark just those ones on sig figs. The problem is you don't know which questions they've picked so yeah, you have to do it for everything

 

[tomp1612]

I got screwed in my trial for sig figs, lost so many marks

 

[Kimyia]

This. They don't mark every question on sig figs- they pick a question(s) and mark just those ones on sig figs. The problem is you don't know which questions they've picked so yeah, you have to do it for everything

Yeah, I've found this going through past papers. Most questions won't have significant figures in the marking criteria but some do and you will lose marks accordingly if you haven't got the right number of significant figures so like deswa said, just be aware to have the right number for all calculation questions.

 

[golgo13]

Just to note i'm quite sure if u write how many dp's or sig fig you're doing it to they won't brutalise on you

 

[someth1ng]

Just to note i'm quite sure if u write how many dp's or sig fig you're doing it to they won't brutalise on you

You're rounding things based on significant figures so you say that it was rounded based on significant figures.

 

[Rawf]

When you're working it out can you write all the numbers out? like
EG: find the concentration of ________ in 0.0122 something...
ANS: n = 0.128497523
c = 0.128497523/whatever
= 0.4923742
= 0.492 (3 sig fig)

As in.. can we just round it to the correct sig fig in the very last step? or do you have to do it throughout all the working steps?

 

[someth1ng]

When you're working it out can you write all the numbers out? like
EG: find the concentration of ________ in 0.0122 something...
ANS: n = 0.128497523
c = 0.128497523/whatever
= 0.4923742
= 0.492 (3 sig fig)

As in.. can we just round it to the correct sig fig in the very last step? or do you have to do it throughout all the working steps?

Normally, I write rounded numbers on the sheet BUT in the calculator, I keep exact values.

 

[Rawf]

Normally, I write rounded numbers on the sheet BUT in the calculator, I keep exact values.

To be honest, in my school exams I usually write a whole lot of decimals like 0.1753 (I round it however I like) lolol. My school never taught us to pay attention to sig figs and they don't care in marking.
however, my chemistry tutor keeps stressing to me that I need to round to the sig figs in the question
do you actually lose marks if you write too many numbers?

 

[someth1ng]

To be honest, in my school exams I usually write a whole lot of decimals like 0.1753 (I round it however I like) lolol. My school never taught us to pay attention to sig figs and they don't care in marking.
however, my chemistry tutor keeps stressing to me that I need to round to the sig figs in the question
do you actually lose marks if you write too many numbers?

In HSC, you CAN lose some marks. It depends on the marking scheme but there's usually 1-2 marks allocated to correct significant figures.

 

[Rawf]

In HSC, you CAN lose some marks. It depends on the marking scheme but there's usually 1-2 marks allocated to correct significant figures.

Woah.. that's pretty silly how they give and take marks just like that.
I thought you might just lose a mark if you didn't write enough numbers (less accurate). So they deduct marks for being more accurate on your answer haha
Thanks for the heads up.

 

[someth1ng]

Woah.. that's pretty silly how they give and take marks just like that.
I thought you might just lose a mark if you didn't write enough numbers (less accurate). So they deduct marks for being more accurate on your answer haha
Thanks for the heads up.

You must understand that giving more numbers ISN'T more accurate. Your answer can only be as accurate as the values you used from the question. Adding more digits is NOT making it more accurate but rather, makes the supposed room for error smaller where it is actually much larger.

However, I believe the whole concept of significant figures is pretty poor. Even BPharm doesn't expect students to answer in certain significant figures - it's usually something like 2 decimal places.

 

[nightweaver066]

Woah.. that's pretty silly how they give and take marks just like that.
I thought you might just lose a mark if you didn't write enough numbers (less accurate). So they deduct marks for being more accurate on your answer haha
Thanks for the heads up.

It's not really being more accurate.

You can only be as accurate as the lowest amount of sig figs used in the question.

 

[Alkanes]

Oh yea guys when calculating pH. Significant figures are used too right? For pH questions, I usually round up to 1 d.p. Can anyone clarify?