calculations (1 Viewer)

[angelicdevil]

hey guys, ive always had trouble in chemistry especially with all the calculations, i seam to get confused in where to put what numbers and what formulas to actually use.. if some one has some handy tips, they would be greatly appreaciated... thanx
angelicdevil

 

[steph@nie]

- MC [T(final)-T(initial)], write as subscripts, H2O, so that you don't forget what numbers to use.
- Titration calculations, draw a diagram showing what amt of what conc of solution you have where.

There's more.. any in particular?

 

[angelicdevil]

thanx for that but mostly when it comes to moles of substances thru a reaction gets me confused.. you know when you got to do mole ratio and use molar mass and moles etc...

 

[steph@nie]

you can draw a triangle, similar to those used in maths for speed, distance, and time, with mass on the top and moles and mm down the bottom.

Always write balanced equations, and refer to equation when working out the number of moles.. it makes it much easier. Eg.H2SO4(aq) + 2NaOH(aq) --> Na2SO4(aq) + 2H2O(l)

From equation, 1 mole of H2SO4 reacts with 2 moles of NaOH
therefore, 0.01 mole of H2SO4 reacts with 0.02 moles of NaOH

and then from there you can do your calculation

 

[angelicdevil]

kool. thanx.. if only i could do equations right..

 

[steph@nie]

hahah. well. I made a list and stuck it up. like acid + base --> salt + water.

 

[angelicdevil]

yea i get those.. its just when it comes to reacting substances i never seam to get the finl product right or it never balances or something like that

 

[Tommy_Lamp]

when balancing always start with the metals, e.g. Lead. Then go onto Carbon, then Hydrogen. if u can balance those and the equation is correct, the Oxygen should balance automatically.

 

[steph@nie]

also, i just remembered, when I have to balance equations, I write down under each side what I have of what, for example, H2SO4(aq) + NaOH(aq) --> Na2SO4(aq) + H2O(l)

Here :H2SO4(aq) + NaOH(aq), I have 3 H, 1 (SO4), 1 Na and 1 O

Na2SO4(aq) + H2O(l), I have 2 H, 1 (SO4), 2 Na and 1 O

from that you can work out what you need doubles of, triples of, halves of.. etc. So I need 2 NaOH's and 2 H2O's and there you have a balanced equation.

 

[angelicdevil]

thanx guys!

 

[milo87]

hey i do chem and only got 9/100 for my trial, i fucked
neone got ne help at all

 

[danno]

i always have trouble on calculations too

but i usually make it up on the long answer ones, cause i just write a whole pile of stuff in the hope that some of it is right

 

[Tommy_Lamp]

hey i do chem and only got 9/100 for my trial, i fucked
neone got ne help at all

Study the course.

 

[danno]

Study the course.

its a bit late for that now

i need to find a last minute study guide thing.

 

[Paroissien]

Although I think you'll need more than 1 day to study. Just pray you do well in your other subjects

 

[Tommy_Lamp]

I wasn't referring to your post.

 

[danno]

i know. i was referring to your post which was referring to his post.

do you know where i can find a last minute study guide? i have a feeling im not gonna do too well in this exam.............

 

[Paroissien]

You'll just have to beg people as quite a few would have done there own major summaries

 

[Tommy_Lamp]

The shortest time that you can study the entire course in depth is about 1mth.
Goto the Charles Sturt University site and quickly browse through their notes, that might help. But if you want my honest opinion, whatever you dont know now your not going to know tomorrow.

EDIT: Or as Paroissien said, you can leech some notes off the resources page. If you find a post from Timmy he has some good concise revision notes linked in his sig.

 

[Paroissien]

I agree with you to a certain extent. If you are trying to learn something you have never seen before, you've got no chance, but if you are just learning some aspects of a syllabus point you'll be able to know it.