The Official ‘O Levels’ Thread

[mohammadyahya]

Re: The Official ‘O Levels’ Thread.

I have AM sessions. My reporting time is 8AM and the paper starts at 9AM.

You should reach the venue by 8 just to be safe.

Thanks

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[AbbY]

Can someone explain the steps required to calculate and identify the limiting reactant? (Chemistry).

You calculate their moles, then see the reaction equation.

Lets say they react in an X:Y = 2:1 ratio, and you have 1 mol X, so X is the limiting reactant... Lets say you have 6 mol of X but only 2 mol of Y, so Y is the limiting reagent and X is in excess.

It's easier to explain with a question. Link me to a question and I'll tel lyou.

Koi bta de !?

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My AM reporting time was 8 and paper began at 9 (though I went at 8:40). I think yours should be the same. A Level and O Level papers begin simultaneously AFAIK.

 

[Xerolt9]

Calculate the mass of Ammonia produced by reacting 57g of Nitrogen and 60g of Hydrogen. Thus, find the limiting reactant. [MENTION=25983]AbbY[/MENTION]

 

[shahzadfootball]

[MENTION=32988]Xerolt9[/MENTION] I cud be wrong since I was doing this in a bus xP but nitrogen is the limiting reactant. And I highly doubt its 69.19g

 

[AbbY]

Calculate the mass of Ammonia produced by reacting 57g of Nitrogen and 60g of Hydrogen. Thus, find the limiting reactant. [MENTION=25983]AbbY[/MENTION]

Why would they ask for a limiting reactant in a dynamic equlibrium question at O Level O_O

Anyway.

N2 + 3H2 -> <- 2NH3

So, N and H are reacting in 1 : 3
N= 57
H=60
and Mol = Mass / Mr , so
N mol = 57/28 = 2.04 mol
H mol = 60/2 = 30 mol

I think it's quite obvious which one of them is a limiting reactant.

Even if it's not,

N : H
1 : 3
2.04 : x
x = 6.12 (Meaning, 2.04 mols of N2 would require 6.12 mol of H2 but you had 30 hence H2 excess, N2 limiting)

OR

N:H
1:3
x:30
x=10 mol

So, 30 mol's of H2 require 10 mol of N2 but there are only 2.xx, hence limiting.

 

[Xerolt9]

I see... Here are a few more questions I have problems with.

Basically, I've understood everything else, it's just some of these calculations that I have trouble with.

^ I know that my formula for ethanoic acid is incorrect. I realized that later.
And it's 20 moles of Carbon Monoxide.

[MENTION=25983]AbbY[/MENTION]

 

[NighteySenpai]

You calculate their moles, then see the reaction equation.

Lets say they react in an X:Y = 2:1 ratio, and you have 1 mol X, so X is the limiting reactant... Lets say you have 6 mol of X but only 2 mol of Y, so Y is the limiting reagent and X is in excess.

It's easier to explain with a question. Link me to a question and I'll tel lyou.



My AM reporting time was 8 and paper began at 9 (though I went at 8:40). I think yours should be the same. A Level and O Level papers begin simultaneously AFAIK.

This shouldn't be allowed...just sayin'.

 

[Anurin]

Why would they ask for a limiting reactant in a dynamic equlibrium question at O Level O_O

Because, CIE. :fp2:

 

[AbbY]

This shouldn't be allowed...just sayin'.

I've went to exams just before the exam begins too. Like reach there at 8:50, get in 8:55 or sth.

Home field advantage, Abuses will lead to ban.

 

[Nabeel95]

This is a really retarded question but it important to write the VI or VII in front of potassium dichromate/manganate. I think I have never done that... Not in the atp either
Also can someone please tell me how the geiger muller tube works. The stuff on the internet is too.. weird. Link me to a suitable diagram too please ^_^
[MENTION=32988]Xerolt9[/MENTION] sorry I was away from PG didn't see the mention. And yeah I did, something about a cruise ship I think? I guess its going to be pretty much the same as hotel/holiday booking scenarios.

 

[Xerolt9]

[MENTION=5716]Nabeel95[/MENTION]: Yes, it IS important to write VI with potassium dichromate. Same with the II in the Copper (II) Sulphate and Iron (III) Oxide etc.

How will you prepare for Computers P3 now that the scenario has been given?

 

[NighteySenpai]

I've went to exams just before the exam begins too. Like reach there at 8:50, get in 8:55 or sth.

Home field advantage, Abuses will lead to ban.

This is dishonourable, unfair and immoral.

 

[Xerolt9]

[MENTION=25983]AbbY[/MENTION]: Help with the questions I posted please? I've got the paper tomorrow ._.

 

[AbbY]

This is dishonourable, unfair and immoral.

Let me add salt to the wounds.

I saw the invigilator going up to the brightest kid in the room and asking him to write his MCQ answers on the calc for a friend (way back in the room) and gave him the answers on the calculator.

Another invigilator was sitting behind me (Physics lab thi, so it was a sink. I was on the left of the sink and another guy on the right.). The guy, who had an uncanny resemblance with Ryan Giggs, sitting behind me kept telling each others answers. (To me, uss nay 1 A 2 B 3C 4D likha hai... Like wise in theory calculations.).

I'm pretty sure you guys had worse experiences

 

[AbbY]

I see... Here are a few more questions I have problems with.

Basically, I've understood everything else, it's just some of these calculations that I have trouble with.

^ I know that my formula for ethanoic acid is incorrect. I realized that later.
And it's 20 moles of Carbon Monoxide.

[MENTION=25983]AbbY[/MENTION]

H3NSO3 moles in 25cm3:

0.105/(3+14+32+16*3) = 0.00108 mol

Neutralization moles (KOH)
conc=mol/vol
0.1=mol/10.8/1000 = 0.00108 mol

So the ratio is 1:1.

Hence, 1 mol of H3NSO3 will react with 1 mol of KOH.


____


CH3OH + CO -> CH3COOH

Theoretical yeild: 10 mol : excess -> 10 mol
Actual yield: 10 mol : excess -> 9.8 mol

9.8/10*100 = 98% (I'm pretty sure this is how it's do be done. Check kerlo)

____

1000cm3 of seawater has 19g of Cl-
25cm3 of seawater will thus have 4.75g of Cl-

4.75g of Cl- = 0.133 mol
1mol : 1mol
so AgCl mols = 0.133

Mass=MolxMr = 0.133 x 143.5 = 19.09g

Sorry I missed them earlier else would've responded then!

This is a really retarded question but it important to write the VI or VII in front of potassium dichromate/manganate. I think I have never done that... Not in the atp either
Also can someone please tell me how the geiger muller tube works. The stuff on the internet is too.. weird. Link me to a suitable diagram too please ^_^
[MENTION=32988]Xerolt9[/MENTION] sorry I was away from PG didn't see the mention. And yeah I did, something about a cruise ship I think? I guess its going to be pretty much the same as hotel/holiday booking scenarios.

In all honestly, it's not necessary. However, I'll suggest you write them. They're not hard. Not at O Levels.

 

[hg1217]

Some tips for maths would be appreciated . I have 4 holidays before the paper, excluding today. Also, i suck pretty bad at it !

 

[shahzadfootball]

^^^^^ do past papers and don't peak through MS ! That is the best way PLUS if u get something wrong,try to figure it out and don't ignore any point which u don't understand ! And make sure u have a timer with u so u have time management as well . best advice during paper is that if u find something even abit time consuming,skip it for a the time and attempt it afterwards when ur done with the paper so ur not wasting time [MENTION=17310]hg1217[/MENTION]

 

[Xerolt9]

[MENTION=25983]AbbY[/MENTION]: Thanks a lot! That really helped

 

[Nabeel95]

@Nabeel95: Yes, it IS important to write VI with potassium dichromate. Same with the II in the Copper (II) Sulphate and Iron (III) Oxide etc.

How will you prepare for Computers P3 now that the scenario has been given?

I dont know really. Past papers. They're pretty easy. I'll do GCSE and IGCSE both. Basically you just need to know how to draw flow charts, draw a web layout, algorithm basics and system development life cycle. The rest is based on your thinking. It never took me more than 20-30 minutes to solve the papers in school.

And how was Chem? I got a some stuff wrong. Not sure about an A* but hoping for I'm pretty confident about an A at least.
This sucks though. I need 7As to get the scholarship in A level. I totally failed urdu first language. I need 5 As in all the other subjects now -.-

 

[Xerolt9]

Chemistry was good, imo. There was nothing I wasn't prepared for.

Some MCQs were confusing, so I think I got those wrong. They were maybe 3 or 4.

Paper 2 was good. Once again, a few 1 mark questions here and there that confused me and might be wrong. Not sure about an A*, but an A seems likely. The ATP paper was really​ good too.