Chemistry: Post your doubts here!

[Busy Buddy]

Dear p4 varient 1 friends, how was the paper today?
Mine went too bad
Don't know why are most of my exams going too bad, although had been working hard.
Is there any chance to at least pass chemistry exam if p4 went toooo bad? Need some help & hope.

 

[Rahma Abdelrahman]

Dear p4 varient 1 friends, how was the paper today?
Mine went too bad
Don't know why are most of my exams going too bad, although had been working hard.
Is there any chance to at least pass chemistry exam if p4 went toooo bad? Need some help & hope.

I messed up the paper as well!

 

[Manobilly]

Dear p4 varient 1 friends, how was the paper today?
Mine went too bad
Don't know why are most of my exams going too bad, although had been working hard.
Is there any chance to at least pass chemistry exam if p4 went toooo bad? Need some help & hope.

it was very tricky .Lots of drawings

 

[Manobilly]

I messed up the paper as well!

InshaAllah everything will go well

 

[Eztair44]

So Whaddya guys think'll be the Percentile of this Paper?

 

[Rahma Abdelrahman]

InshaAllah everything will go well

I hope so.
In shaa Allah!

 

[Hinafatima]

Hi everyone
I've started a site which will provide you with solved papers showing all the steps in the working and with useful tips on the side. The best part is that when you look at a solved paper, you can look at commonly made mistakes and learn from them.
Please do check it out!
https://sites.google.com/site/fromatoscom/home

Hi!, is it only for 2012 and 2013 or r u going to add for other years too?? thanks a lot

 

[hope4thebest]

For starters, Lattice Energy can be either positive or negative. Depending on wether youre talking about bond breaking or bond formation. However with reference to how the Born Haber Cycle was formed in that question, Lattice Energy was exothermic.
Secondly, the electrode potential was -0.19V
Reason?
The reduction potential of 1 mol/dm3 was -0.13
Pb2+ + 2e <----> Pb -0.13V
Since the concentration is less than 1 mol/dm3, the equlibrium will shift to the left and think about it this way. It will be even more difficult to reduce so reduction potential will further decrease
Hence 0.19
Now for graph
first of all graph ended at 12.5. Final pH was 12.5
Inital ph was I think, if I remember correctly, 2.8
There would be a very small steep graph initally as the acid was weak
Then a buffer would be formed so slow rise in pH until 10 cm3
Steep vertical portion at 10 cm3
End point above 7
Finally pH would be 12.5
I found Question 1 Part 2 a little difficult
Didnt know what to write
Also the question where he converted -CONH2 to -CH2NH2
I thought about it
Hes reducing
So I just used LiAlH4, not NaBH4, since NaBH4 since it is weak. And I was right.

lattice energy is always exothermic as only bond formation takes place

 

[AnujaK]

No I'm gonna post more I think there are already others though

Hi!, is it only for 2012 and 2013 or r u going to add for other years too?? thanks a lot

 

[istudent]

can anybody who gave 9701 p42 tell final [OH-] and final pH

 

[sumeru]

can anybody who gave 9701 p42 tell final [OH-] and final pH

0.033 and 12.5

 

[omarjaved619]

Drawing with pencil is optional right? Or is it a must?

 

[istudent]

0.033 and 12.5

can explain how?

 

[hope4thebest]

0.033 and 12.5

same same

 

[Musab100]

All those saying the paper was shit easy
Agreed
BUT
it was trickier than most people here think it was
I can bet my life most people got the Electrode Potential Wrong
Seemed simple I know
Wasnt exactly what it seemed.
I could go on and on about the various small stuff in the paper which people are presuming to be easy and werent exactly straightforward but paper discussion is not allowed
Secondly
Grade Thresholds dont vary much. Difficult papers have grade thresholds around 62 for paper 4. Medium Difficulty is 65. All those saying grade threshold will be 76-77 for this paper have got to be shitting me
It was easy, agreed but its not like everyone around the world is just a fcking brilliant super genius all of a sudden this year. If grade thresholds were that variable, then they should fall to around 52 during difficult papers which they do not.
The person who said grade threshold for A* will be somewhere around 230?
lol
Generally the grade threshold for an A* is say around 200. Easy papers? Goes up to at max, at max 210. Thats it.
230/260 is unrealistic.

i completely agree with you

 

[BeBeskii108]

What are indicators that can be both used to identify acid and alkaline ?

 

[BeBeskii108]

Another question. How do you find Slope of the graph in paper 5. Is it like finding a gradient ? if so Can I choose random 2 points ? How do I draw the construction lines ?

 

[omarjaved619]

Ok so in a Paper 5 , in a planning question, they asked us to mention how we would dry the precipitate. In the Answer scheme, the gave a few methods along with "NOT heat or the use of a Bunsen..."

The next question asked how we would ensure the precipitate was thoroughly dried. The answer went like
"The drying process should be repeated to constant mass . ALLOW HEAT/REHEAT to constant mass/weight."

What is this cwap?

 

[omarjaved619]

Another question. How do you find Slope of the graph in paper 5. Is it like finding a gradient ? if so Can I choose random 2 points ? How do I draw the construction lines ?

Yes. Slope is the gradient. You can choose any two points which are sufficiently apart. The construction lines are just a big triangle against the line. Kinda like this https://www.google.com/search?q=fin...gebra%2FStraightLinesin2D%2FSlope.htm;707;453

 

[Snowysangel]

It says in he examiners report that removing ammonia in the harbor process STOPS the backward reaction? Wth I thought both reactions always occur...just that one of them proceeds at a faster rate ie the rate if reaction increases. What does the position if equilibrium mean exactly? That the yield of either the backward or forward reaction increases...I know..but HOW?