Biology; Chemistry; Physics: Post your doubts here!

[danial 234]

dani boy,Please tell wht u think wud be the answer now coz there r Fe3 ions as well

will tell ya tom. ok

 

[M.Omar]

will tell ya tom. ok

Alrighty then...

 

[Zuhsid]

Umm, how am I suppose to explain?
Okay so, we have a question for instance, it doesn't directly ask you to find something, right? How do you determine a formula to solve that particular question? I get really confused. I don't know what to use. Which formula to apply and when..

Well you only need to know the 4 basic formulaes...... as far as the questions are concerned, the thing is, that first see n the questions that what are the values given(and of what substance), such that there should be atleast 2 values that could be fitted into any one of the formulaes(one should be missing)....and when you find the missing value, see if thats what they are asking for, if not, then see what it wants, and now see which formulae contains the obtained value, the value that is asked, and a value which is already given in the question..... So this way you can solve it!!

But if you do not understand any question(in past papers etc..... just write the question in one of the forums, and someones bound to respond!!

Hope it helps!!

 

[Sadi66]

Please tell me which book should we rely on in O level Biology, as the Marry Jones Cambridge Biology uses very little details but its endorsed one, so what should we do?

 

[Nabeel.Ahmad]

Please tell me which book should we rely on in O level Biology, as the Marry Jones Cambridge Biology uses very little details but its endorsed one, so what should we do?

Federal.

 

[shameema]

Federal.

well in our school we used the comprehensive biology , and it had ample info

 

[shameema]

In titration questions, is it necessary to show your workings?
And in mole concept things, would it be alright if we use a different approach from whats mentioned in the marking scheme? They give marks separately for finding moles, but in some cases we can directly derive the answer with the help of the equation, right?

yes, the working is necessary @lst the mole ratios have to be shown. there are several ways to get the answer using the equation wld b sufficient

 

[Ram97]

In titration questions, is it necessary to show your workings?
And in mole concept things, would it be alright if we use a different approach from whats mentioned in the marking scheme? They give marks separately for finding moles, but in some cases we can directly derive the answer with the help of the equation, right?

Dunno about titration but for moles you need to show your working cuz it carries marks

 

[M.Omar]

Salam
I wanted to seek ur opinion abt this answer of chm atp paper as per the mark scheme..In may june 2006 in the titration question of ATP.They asked for wht is the colour of the mixture of iron(2) sulfate and iron(3) sulphate .The mark scheme reads as Colorless/green .Any ideas of how it is this color or even being colorless

As a call to all,Anyone feel free to suggest their ideas of how this is answer is to be arrived at.I can think of this is tht since distilled water and H2SO4 is colorless and there very few moles of iron 2 and iron 3 ions relative to the solvent,chances r tht it forms a very pale color or even colorless solution so thts how the answer is to be arrived..Anybody,do give ur helpful thoughts abt this one.

 

[irfan.kheerdali]

Describe the structure of a seed, stating the functions of the features you mention[7].
Describe and explain the processes that occur when a seed germinates[3].
Explain what is meant by the term pyramid of numbers[4].
Explain the fact that energy flow is non-cyclical[6].

 

[shameema]

guys i recommend you buy the red-spot books they come in handy esp for essay type ques

 

[irfan.kheerdali]

Explain how a knowledge of genetics has helped breeders to improve the quality of wool
produced by sheep

 

[irfan.kheerdali]

Describe the part played by genes in the process of evolution

 

[irfan.kheerdali]

explain how natural selection may lead to evolution

 

[Jenn]

11) all ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
a) 0.5 mol (NH4)3 PO4
B) 0.5 mol (NH4)2 S03
C) 1.0 mol NH4Cl
D) 1.0 mol NH4NO3

How do we get to the answer?

Kindly help. Thankyou in advance.

 

[bryan007]

helo plzz help for physics o level june 2011 qp 12 question no 2 why D why not C???

 

[Iridescent]

helo plzz help for physics o level june 2011 qp 12 question no 2 why D why not C???

It is C. Here's the marking scheme:
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_ms_12.pdf

 

[bryan007]

th

It is C. Here's the marking scheme:
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_ms_12.pdf

thxx soory just misunderstood it'

 

[zeeshma]

have you ever find answers given in marking scheme are wrong ,somtimes(chemistry)?

 

[zeeshma]

11) all ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
a) 0.5 mol (NH4)3 PO4
B) 0.5 mol (NH4)2 S03
C) 1.0 mol NH4Cl
D) 1.0 mol NH4NO3

How do we get to the answer?

Kindly help. Thankyou in advance.

convert moles into mass for all salts
a ad b can give two moles of ammonia
c and d can gve one mole of ammnia
find massof all the salts
divide mass of moles produd=ced by each salt divided by total mass f the salt and multiply it with mass of salts given in the questin(u already have conv
erted mles into mass in first step