1.2/S1.4.4 Determine empirical formula from the % composition/other data [SL IB Chemistry]

Find the MOLES of each element and then simplify the ratio between them.
Eg 24g of Mg is combusted in oxygen to produce 40g of magnesium oxide. What is the empirical formula of this product?

Mg 24g / 24g/mol O (40g-24g) / 16g/mol = MgO

[KatsAndBees]

thanks so much for doing this for ib chem students everywhere, like all these vids in general, thank you

[gabyfuentes]

yesss!!!! IB tests soon & i needed this to review!

[ibchemvids]

Double everything to get rid of the half! (turning 1.5 to a 3)

[ibchemvids]

@Malpiedimma since y /2 = 0.5, then y=1

[moeizahmed]

Hey, I know you have already explained this in the comments but I still do not understand why the coefficient for H2O is y/2. But for CO2 you just left it as just x. Did you put the y/2 because H2O is just something that is always produced in that form for hydrocarbons or is their another reason?

[ibchemvids]

the number of C is x since we do not know what chemical we are using yet.
The number of H is y for the same reason
every C in my molecule makes a CO2 BUT
every 2H in my molecule makes a H2O

[malaikadsouza]

Hey Mr.Thornley, In your evil question I wasn't able to understand from where the y/2 for the H2O came from.

[rottenrafflesia]

okay I understand now...thank you :) Amaze by how fast you reply.

[ibchemvids]

eg if we were using C8H18 then we would make 9 H2O

18 --- 9, y

[shoothoops]

Hi Sir,

in your evil question, i can't quite understand why the 0.25 moles calculated from CO2 is equal to 0.25 moles of C in the hydrocarbon. How can the ratio be exactly the same if the Mr of Carbon is only (12/44) of the whole Mr of CO2?

[ravenkid]

Where do you get these questions from, do you make them up yourself? I want to practice more questions like these.

[Malpiedimma]

isn't it c1h2? as i thought it would be H 0.5/0.25 rather than the 1

[Malpiedimma]

@richthornley ahh of course thank you very much, and great videos!

[busolabiran]

Would the first question using the percentages of elephants and horses be on the calculator paper? I wouldn't be able to divide 37.5 by 600 in my head.

[tianzexia]

in the last evil question, why is oxygen "O2"? the question just says excess oxygen, but not oxygen molecule, so why isn't it just "O"?

[SamTheoAwesome]

PoT WoB - Percentage on Top, Weight on Bottom ;)

[misstuhin]

decimal places in the molar mass? (as in, in the working out?)

[HamzaG]

but what if i have to round 1.5 to an integer should i write 1 or 2

[amumuyanga]

I still don't understand.Please help. Thank you.

[tianzexia]

what do you mean by "the smallest number"?