IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: nonelee on June 02, 2009, 10:14:10 am

Title: MOLES question.
Post by: nonelee on June 02, 2009, 10:14:10 am

i am taking coordinated science this week.
and i have a question please answer (:

theres a formula for calculating moles right?
but i forgot, please tell me.
and there are also something else related to moles.
i forgot too. so again, please answer. thanks!

Title: Re: MOLES question.
Post by: idk on June 02, 2009, 10:26:19 am

Number of moles=given mass of substance divided by( / ) atomic or molecular mass of the substance.
for eg-given mass  of a piece of coal(carbon)=24g. at.mass of carbon=12
therefore number of moles=24/12=2 moles
best of luck and Take care.

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 10:30:40 am

finding the mole using the realative atomic mass:

mole = mass used / relative atomic mass

finding the mole of a compund:

mole = mass used / relative molecular mass

finding the mole in a solution:

mole = volume (dm^3) * molarity

finding the mole of any gas:

mole = volume (dm^3) / 24 dm^3

finding the percentage yield:

% yield = (mass produced / theoretical yield) * 100

finding the percentage purity:

% purity = (actual mass reacted / initial mass used) * 100

hope this helps  :)

Title: Re: MOLES question.
Post by: nonelee on June 02, 2009, 10:34:43 am

thank you people :D
but i remember theres this formula which needed volume?
i forgot..

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 10:36:21 am

Quote from: nonelee on June 02, 2009, 10:34:43 am

thank you people :D
but i remember theres this formula which needed volume?
i forgot..

i added it  ;)

Title: Re: MOLES question.
Post by: nonelee on June 02, 2009, 10:37:19 am

thanks again (:
do you take coordinated science too?

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 10:38:56 am

Quote from: nonelee on June 02, 2009, 10:37:19 am

thanks again (:
do you take coordinated science too?

nope, i take the normal chemistry :)

Title: Re: MOLES question.
Post by: nonelee on June 02, 2009, 11:12:54 am

oh...why? like a lot of people are taking them separately.
which one is harder you think?

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 11:14:51 am

Quote from: nonelee on June 02, 2009, 11:12:54 am

oh...why? like a lot of people are taking them separately.
which one is harder you think?

im not sure, i know nothing about co-ordinated science, and my school were not offering it as an option.

thanks  :)

Title: Re: MOLES question.
Post by: nonelee on June 02, 2009, 11:16:58 am

oooh okay. (: thanks again.

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 11:18:00 am

Quote from: nonelee on June 02, 2009, 11:16:58 am

oooh okay. (: thanks again.

no worries,

and gd luck in ur science exam  :)

Title: Re: MOLES question.
Post by: nonelee on June 02, 2009, 11:23:55 am

oh let me ask one more.
whats the formula for resistance?
is it voltage/current? or the opposite?
im confused..

Title: Re: MOLES question.
Post by: Q80BOY on June 02, 2009, 11:27:55 am

Quote from: nonelee on June 02, 2009, 11:23:55 am

oh let me ask one more.
whats the formula for resistance?
is it voltage/current? or the opposite?
im confused..

that's ohm's law,

resistance = voltage / current