Percentage Yield | A-level Chemistry | OCR, AQA, Edexcel

[@haphuochuy3475]

In question 3, nH2=1.75 mol; nO2=0.9375; however, based on the reaction 2H2+O2->2H2O means that H2 is limiting reactant, and nO2(react)=1.75/2=0.875 mol. so, nO2(left-over)=0.9375-0.875=0.0628mol. Therefore, O2 cannot be limiting reactant. As a result, yield percentage must calculate based on H2.

[@ismael2901]

I knew there was something wrong because u only need 28g of O2 but we have 30 grams

[@SevenStepsAhead]

shit

[@huongle4129]

limiting reagent is H2, not O2 because in the equation the ratio between them is 2:1 not 1:1. Anw, thanks for your nice video!

[@MF-qf3st]

there's a big 2 in front of the hydrogen which multiplies both hydrogen and oxygen, so in fact she is right the limiting reagent is H2

[@scottmorris3116]

@@MF-qf3st i think she is wrong because the big 2 refers only to the H2. This means that 2 moles of Hydrogen reacts with 1 mole of Oxygen. It also means that 1.75mol of H2 reacts with 0.875mol (option 1) of O2 or that 0.9375mol of O2 reacts with 1.875 mol of H2 (option 2). Now, considering we only have 1.75 mol of H2 and 0.9375mol of O2, only the first of those 2 options can work because there isn't enough H2 to carry out option 2. This means the H2 is limiting so the calculation must be based on that. @SnapRevise, please could you clarify if you made an error.

[@imjustmartyn4961]

Could listen to you talk all day, lovely voice to listen to. Very helpful video, and helped me out a bunch! Thanks!

[@shahzaibbio]

While determining the Limiting Reagent, it is important to consider the ratio in which the reactant combines with the other reactant(s). This can be found out using a balanced chemical equation. Even though Oxygen seems to be in a lesser quantity, it is in excess when considered within the ratio it is needed, i.e. 2 Moles of H2 need 1 mol of O2. Therefore, 0.9375 mol of O2 would require double the amount = 1.875 mol of H2 to react completely, which isn't there. So the limiting reagent is H2.

[@eshen156]

i still dont get it

[@gamerglim]

15:40, ma'am I have a question. Why did you multiply the total % yield with the moles of Asprin???

[@ald4619]

Same. Replay if u got it please

[@veryvery454]

Limiting reagent is H2

[@hughyurfeee8229]

ywa

[@yf1up378]

0.9375 x 2 = 1.875 not 1.825

[@aleenaasif4712]

yes

[@SevenStepsAhead]

yup

[@SevenStepsAhead]

@SnapRevise please clarify the answer for question 3

[@urwahxx3399]

Okay so at first I didn’t understand the comments that said the limiting reagent is H2 but in my head I kinda knew it was because the hydrogen and water have the same ratio ie 2:2. So n.o of moles of H2= 3.5/2= 1.75 and n.o of moles of O2= 30/32=0.9375 So because there’s different ratios of the oxygen and hydrogen, to get the limiting reagent you multiply the n.o of moles of O2 by 2. So 0.9375 x 2= 1.875. So now I have my oxygen, hydrogen and water in a 2:2:2 ratio. You could even divide the n.o of moles of hydrogen by 2 to get 0.875 moles of oxygen since there’s two times more hydrogen than oxygen. So now you have your moles of oxygen which is 1.875 and your moles of hydrogen which is 1.75 so obviously 1.75

[@Cosxmix]

bruh I really didn't even understand this Im actaully gonna fail pray for me

[@aamna3437]

lol im praying

[@apricot212]

try a different channel. i dont remember what its called but just type in Melissa Maribel and you'll see it

[@Cosxmix]

@@apricot212 yeah i just started watching her shes proper usefull

[@MarshaIII]

@@Cosxmix did you pass the exam

[@emancipationproclamation3466]

5:36 you didnt take into consideration the coefficient in front of the ethane when calculating its total mass?

[@shishidoseijuro7770]

woah babatunde calm down jeezas

[@annerangel1007]

Also in 11:05 for hydrogen...I´m confused...

[@Saif_4229]

no you ignore coefficients when calculating total mass

[@alexbarnett6488]

kuntaekuntae gomes don’t know if it helps now but moles = mass / molar mass. the mass takes into account the coefficient as it’s the total mass of the compound, if you took into account the coefficient in the molar mass too then the two would cancel eachother out so, for example, you’d be finding the moles in H2O instead of 2H2O

[@RBS.10]

Emancipation Proclamation you dont use the coeficient in the MASS

[@somebodygr8845]

did she do question 3 right or wrong? because I'm pretty sure H2 is the limiting reagent

[@akshaysingh6087]

Great deed love from india

[@janwincote7260]

Can I just ask why you sometimes work to 3 dp and don't round up and then other times you do then with the next calculation your working to 2dp and you are round up even though in the same equation you have already not rounded up? Didn't know if there was a specific reason for this that I have missed. Thanks. Great videos by the way.

[@nunushianii]

in Q4 why do you multiply the mol value (8621 mol) by 0.706? if the ratio is 1:1?

[@munir5915]

yes i’m also wondering the same thing

[@rileydavies74]

you x 0.9375 by 2 wrong

[@MegaLionking777]

Best ever explanation

[@jamesramplin8124]

No it isn't. She gets questions wrong. H2 is the limiting reagent

[@MyAbdul111]

@@jamesramplin8124 why tho

[@jamesramplin8124]

@@MyAbdul111 2 H2 + O2 -> 2 H2O There are 2 H2. So for every 1 mole of Oxygen 2 moles of Hydrogen are used up. 1.75/2 = 0.875 which is lower than the moles of Oxygen (0.9375). If Oxygen was the limiting reagent then the moles of Hydrogen would need to be double 0.9375 (over 1.875 moles of hydrogen would mean hydrogen is in excess). The later videos seem to make less mistakes but I advise you stay skeptical and use multiple sources for revision.

[@siddikabegum393]

Hi, Would it be possible for you to make a video on a walkthrough on the AS Chemistry paper H302/01 Breadth in Chemistry as I am struggling with a couple of the multiple choice questions. Thanks!

[@StudylifemitAva]

Is it not true that in the exercise H2 is a limiting reactant ?!!!

[@shuaibmmm]

Thanks a lot, I found it really helpful 👍 keep up the good work.

[@syedhassan306]

A walk in the Jurassic park

[@SodiumInteresting]

Piece of nitrogen and hydrogen cake 🎂 😆

[@SevenStepsAhead]

lmao yes

[@hamzasheikh4273]

What doesn’t make sense is that she’s calculated the moles of ethane but what doesn’t make sense when calculating the moles of carbon dioxide she calculated mass it’s already given the mass ?

[@sadiyosharaf1318]

I got confused 1.066mol where is it come from?

[@voyager1996]

4:45 7:56

[@jeffersonjeremiah1730]

Hydrogen is the limiting reagent.

[@naseerap7417]

1.825x18=32.85 not 33.75

[@a.2169]

That’s because 1.825 is not the correct value. It should be 1.875

[@naseerap7417]

@@a.2169 ohhh okay thanks :)

[@Sunshine-xo3np]

I can’t find percentage yield anywhere in the aqa spec

[@hamsanmuhammad9534]

You can improve your video,i hope next video would be better;)

[@pigeonlove]

You could improve your grammar 😉

[@Thedrowningduck]

@@pigeonlove You did not end the comment with a full stop. You can also improve your grammar. ;)