1,000,000 Question Thread :D

[m@tty]

It would need to be to one significant figure, because of 5g. Therefore 0.04mol.

[kenhung123]

In summary, only zeros that are between non zero digits and after are significant right? E.g. 0.303 is 3 sig fig
0.300 is 3 sig fig
0.003 is 1 sig fig?

[Edmund]

In summary, only zeros that are between non zero digits and after are significant right? E.g. 0.303 is 3 sig fig
0.300 is 3 sig fig
0.003 is 1 sig fig?

Yeah

http://vcenotes.com/forum/index.php/topic,17173.0.html

[kenhung123]

Oh, wait 300 is 1 sig fig? 300. is 3 sig fig?

[m@tty]

Isn't it 3?

[Edmund]

Isn't it 3?

Yep, 300 has 3 significant figures. If you have to express 300 in 1 decimal place, then it would be . If 2 decimal places, then etc...

Hope this helps...

[kenhung123]

Hmm I was told if you don't put decimal point the zeros are not sig. So 300 is 1 sig fig and 300.0 is 4!? I find it strange too!

[Edmund]

This guide will answer everything

[kenhung123]

I get it Thanks!

In fact the decimal point presence does matter!

E.g. 4000 in scientific form is 4x10^3 1 sig fig
      4000. in scientific form is 4.000x10^3 4 sif figs!
      4000.00 in scientific form is 4.00000x10^3 6 sig figs!
So just change the answer into scientific form remembering the decimal point and you can work out the sig figs easily. Other than that remember non zero digits, zero between numbers, zeros after non zero numbers both on the right of decimal point are sig. Zeros left of a decimal point are sig but if no decimal point it is not sig!

[Edmund]

1 significant figure:
2 significant figures:
3 significant figures:
4 significant figures:

About the decimal point thing, was that non existent? 400 as 1 sif fig and 400. as 3?

Both have 3 significant figures.

[kenhung123]

1 significant figure: = 500
2 significant figures:

About the decimal point thing, was that non existent? 400 as 1 sif fig and 400. as 3?

Both have 3 significant figures.

Yea. I guess the decimal is sig.

2 sig figs are not reversable btw. 5.0x10^2=500. but does not equal 5.00x10^2...

[kenhung123]

Question:
An impure sample of iron (III) sulfate, weighing 1.545g, was treated to produce a precipitate of Fe2O3. If the mass of the dried precipitate was 0.315, calculate the percentage of iron in the sample.

Mr(Fe2O3)=159.6 Mr (Fe)=55.8

[Edmund]

First find the moles of precipitate:



Then find the number of moles of Iron (Fe) in this precipitate:



Now find the mass of iron (all the iron came from the impure sample):



Therefore the percentage is:

[kenhung123]

First find the moles of precipitate:



Then find the number of moles of Iron (Fe) in this precipitate:



Now find the mass of iron (all the iron came from the impure sample):



Therefore the percentage is:

I have found m(Fe2(SO4)3) why is it just finding Fe?

Thanks Edmund

[Edmund]

The question specifically asks to find the amount of Fe present in the sample and is already given as 1.545g