-=important=- (1 Viewer)

[toknblackguy]

well maybe not that important
but certainly don't wanna throw away marks
the volume constants you use in working out how much gas is evolved with moles and stuff
standard temp 0 - moles = V/22.41
room temp 25 - moles = v/24.47

you can lose marks here!
apparently (although it hasn't in the past) these constants vary each year!
so refer to the data sheet to use the correct one
there's no point throwing away marks like this!

just though i'd mention it

 

[mercury]

read the back of the periodic table that's gonna be attached and don't be a smarty pants

 

[toknblackguy]

hehehe
i dunno...a friend's tutor warned me..i'd rather not lose a mark for something so stupid
that's all

 

[saz]

while we're talking about calculations.....

i was reading through Frigids excellent notes and noticed that in the AE when calculating amounts for titrations that the amounts for volumes werent converted into litres, i.e. divided by 1000.

I was wonderin if someone mite be able to explain to me why? i always thought the formula was moles = conc x vol(L).. plz tell me i havent been taught completely wrong all year!! thanks

 

[toknblackguy]

it is supposed to be in litres!
woah..did frigid actually make a mistake?!?

think of it this way: conc=moles/vol
and conc is measured in moles per litre...get it?

 

[Frigid]

sorry saz, that would be because i made a typo... you are perfectly right, all the volumes should be in litres.

 

[saz]

Ah ok... thanks That one was stressing me out a bit....

 

[fitz33]

whats the go with significant figures?
are u supposed to round off all calculations to the correct amount of significant figures or should u only do it at the very end?

different trial papers do different things and im just wondering what they want for hsc

 

[Frigid]

i think you give the same amount of significant figures as the data in the question.

 

[sneaky pete]

Umm yeah they changed it from 101.3 kPa to exactly 100 kPa
at 0 C is 22.71 L and 25 C is 24.79.
Just remember to use the values on the sheet they give you and you'll be fine

Originally posted by fitz33
whats the go with significant figures?
are u supposed to round off all calculations to the correct amount of significant figures or should u only do it at the very end?

Use the full value when you can do further calculations, and only at the very end should you round of to sig fig's or decimal places.

Just say your trying to find out the mass of something and earlier on you found the moles to be 0.134352545, use that full number in the n = m/mw, and dont use just 0.1 or 0.13.

 

[hipsta_jess]

Originally posted by sneaky pete
Use the full value when you can do further calculations, and only at the very end should you round of to sig fig's or decimal places.

Just say your trying to find out the mass of something and earlier on you found the moles to be 0.134352545, use that full number in the n = m/mw, and dont use just 0.1 or 0.13.

yeah, we did one in class and the girl i was working with rounded off straight away and didnt tell me, and by the end, we ended up with a figure like 3 or 4 different than everyone else. its amazing how much difference can be caused by rounding off too early.