Biology; Chemistry; Physics: Post your doubts here!

[sweetiepie]

oh okay hows that notes

 

[RabeeaAhmad1996]

This is awesome that you are helping all those troubled students(like myself) with their problems .so thumbs up for u :good: .
My questions are related to chemistry.

I always get confused about the chapter moles-even though it's the easiest one there is. I just can't seem to understand what the question is asking let alone try to solve it.things like limiting reactants,and the titration qs in ATP. there are so many formulas that it gets very difficult to remember. Also the topic Acids and bases is difficult because i cant understand how different ppts are made of random compounds. How do we test them? how can I know which experimental technique to use to identify it?
I really really need your help.

 

[SalmanPakRocks]

This is awesome that you are helping all those troubled students(like myself) with their problems .so thumbs up for u :good: .
My questions are related to chemistry.

I always get confused about the chapter moles-even though it's the easiest one there is. I just can't seem to understand what the question is asking let alone try to solve it.things like limiting reactants,and the titration qs in ATP. there are so many formulas that it gets very difficult to remember. Also the topic Acids and bases is difficult because i cant understand how different ppts are made of random compounds. How do we test them? how can I know which experimental technique to use to identify it?
I really really need your help.

Mole in tritration = free marks.
Listen moles ain't easy, its just complicated but once u get the hang of it u'll do it with ease.
There are lot of things inter-related like Limiting reactants u just named.
Try studying those test from the book and then solve ATP past papers, the pattern for moles titration is almost similar. If ur stuck at any question then post it here and we'll try our best to help u.

 

[sweetiepie]

This is awesome that you are helping all those troubled students(like myself) with their problems .so thumbs up for u :good: .
My questions are related to chemistry.

I always get confused about the chapter moles-even though it's the easiest one there is. I just can't seem to understand what the question is asking let alone try to solve it.things like limiting reactants,and the titration qs in ATP. there are so many formulas that it gets very difficult to remember. Also the topic Acids and bases is difficult because i cant understand how different ppts are made of random compounds. How do we test them? how can I know which experimental technique to use to identify it?
I really really need your help.

hmm okay

 

[scouserlfc]

oh cmon that ppt test question is the most easy one u get free i think 8 or 9 marks for that.
try remembering by writing them in a friendly manner on a paper and then learning them by making some mnemonics like there are metals which share the same ppt. like ZINC,Al and partially for Ca .
Zn and Al are easy they are amphoteric so in both NaOH and NH3 they remain white and dissolve but aluminum in Nh3 excess is insoluble so AL and Zn are both same except for this difference.
now Cu is so easy remember its common blue colour we think of when we think of Cu and since the same result is found for both NaOH and NH3 except in NH3 it dissolves and forms a dark blue solution so u can easily remember it,NOW fe +2 and +3 are pretty easy and for Ammonium u know that reaction that alkali plus Ammonium salt equals ammonia gas and other products so no problemmmm ! just give it time,im pretty sure u are one of chem haters !

 

[ailg1996]

Plz can sum1 solve this question i keep getting the w
wrong answer
according to marking scheme answer is 900 cm3

 

[SalmanPakRocks]

Hmmmm which year is it? R u sure its 900cm^3 ? Cuz I think its 450cm^3

 

[VelaneDeBeaute]

Yeah! Even i got 450 cm^3!

 

[Anon]

ms is wrong...

I too am getting 450..

 

[ailg1996]

Here is the ms
it s from w05 paper

 

[Silent Hunter]

IF I remember correctly this is also a mistake.

 

[Anon]

A problem in Pysics paper 1 :

 

[VelaneDeBeaute]

Is the answer D?

 

[Silent Hunter]

yes... mine too... its D it think

 

[Anon]

Yup, why?

EDIT: Why shouldnt it be C?

 

[VelaneDeBeaute]

^ Because the light ray enters at a perpendicular angle to the glass surface so it must pass straight through the glass medium! In the diagram they show that it bends, therefore it is wrong!

 

[Silent Hunter]

in C the ray is falling at normal (at 90 degrees) and when anything falls at 90 it does not change direction and its happening here..... and later when it emerges out of the perspex the angle changes (not 90) and so it bends away from the normal... so this ones correct

 

[Anon]

I see I see,
I didnt knew that ray dont turn when it enters at 90.
Thanks

 

[Silent Hunter]

yes it s basic point.......... applies at many places .. like here

 

[VelaneDeBeaute]

^ The explanation for C is right!