Biology; Chemistry; Physics: Post your doubts here!

[Shahmeer Khan]

Will any one help me .... paper with which code is for Pakistan !! 21 or 22 and 11 or 12 ....... Help me please !!

 

[mohdumar]

Will any one help me .... paper with which code is for Pakistan !! 21 or 22 and 11 or 12 ....... Help me please !!

22 and 12

 

[papajohn]

Anyone please

Q) Which statement about ethanoic acid is correct?
A It contains three carbon atoms per molecule.
B It contains five hydrogen atoms per molecule.
C It is insoluble in water.
D It reacts with ethanol to form a sweet-smelling compound.

 

[ammarfarman]

HI
Can u plz send me the questions from the past papers according to the topic moles,electricity and chemicals, energy from chemicals.

 

[Wizzyness]

Hey. I am a bit new here and I need a little help regarding O Levels.
Firstly, I want to ask that if someone has appeared for O level exams in Oct/Nov as a private british council candidate does he/she has a chance in getting a distinction? Secondly, what exactly is the criteria of a distinction? is A* a distinction? Like if u get an A* means its a distinction or what? Thirdly, how does cambridge mark on Urdu A (O-levels) and Sciences subjects and English Language ( O-Levels). Can anyone give me an tips regarding english? Like anything I have to be careful about while attempting the paper. Also, I heard that if your writing is not perfectly neat (illigible still), the examiner deducts your marks. how true is that? Lastly. I want to take tuitions for chemistry. I heard sir. KRC is very good. the academy where he teaches is like really close to my house so I am considering him. If someone has been his student, can they tell me what type of a teacher he is? Just to have a general idea so i know that my decision is right since i am pretty bad in chem and need help. i know, lots of questions. sorry. but i really need help. please be kind enough to reply. thank youu.

 

[mohdumar]

what products are formed in electrolysis of aq. KBr ? can anyone explain with ref to reactivity series? Im confused about the Anode part

 

[papajohn]

what products are formed in electrolysis of aq. KBr ? can anyone explain with ref to reactivity series? Im confused about the Anode part

Metal always deposited at the cathode.Whereas at Anode, the gas liberated.The Potassium is in the top in reactivity series, so it readily discharge at the cathode.
At anode reddish bromine gas liberated

 

[nidz]

Basically it means that if u add water before adding ethanol you would have observed an emulsion straight away and hence it is required u add ethanol first or else u will get the emulsion also it says that by convention u add ethanol first the more lame it looks it is the correct answer and dont be surprised to find more lame answers in MS for Bio ATP they really think bio students are too stupid and hence such answers are seen

Haha thanks a lot for your answer

 

[mohdumar]

Metal always deposited at the cathode.Whereas at Anode, the gas liberated.The Potassium is in the top in reactivity series, so it readily discharge at the cathode.
At anode reddish bromine gas liberated

these wernt the answers!!!! IN MARKS SCHEME liquid bromine and hydrogen gas was the answer...

 

[Queens]

these wernt the answers!!!! IN MARKS SCHEME liquid bromine and hydrogen gas was the answer...

yes potassium is more stable as an ion so it wont discharge , and H+ being less reactive will be discharged. Bromide is less reactive then hydroxide and will therefore discarge.
Just keep the reactivity series in mind. The less reactive elements discharge in preference to the more reactive ones.

If you didn't understand , let me know i can explain in more detail.

 

[Queens]

Metal always deposited at the cathode.Whereas at Anode, the gas liberated.The Potassium is in the top in reactivity series, so it readily discharge at the cathode.
At anode reddish bromine gas liberated

Back to chemistry class papajohn.
Bromine is a liquid at rtp , not a gas and would be discharged at cathode. Potassium will NEVER be discharged in its aqueous solution, let alone readily. Your answering questions wrong. I appreciate your will to help but don't misguide people.

 

[scouserlfc]

Back to chemistry class papajohn.
Bromine is a liquid at rtp , not a gas and would be discharged at cathode. Potassium will NEVER be discharged in its aqueous solution, let alone readily. Your answering questions wrong. I appreciate your will to help but don't misguide people.

Metal always deposited at the cathode.Whereas at Anode, the gas liberated.The Potassium is in the top in reactivity series, so it readily discharge at the cathode.
At anode reddish bromine gas liberated

Dont worry people its good u get ur mistakes now or else it will be a really hard lesson to learn, keep revising chemistry,bio and physics at least fortnightly you will eventually even start remembering the minor details and dont rote learn please try understanding it will even come good in A Levels

 

[papajohn]

I conclude my statement

 

[mohdumar]

yes potassium is more stable as an ion so it wont discharge , and H+ being less reactive will be discharged. Bromide is less reactive then hydroxide and will therefore discarge.
Just keep the reactivity series in mind. The less reactive elements discharge in preference to the more reactive ones.

If you didn't understand , let me know i can explain in more detail.

i do know about preferential discharge but i thought the series for anions was

OH- I- Br- Cl- NO3- SO4-2 F-

with hydroxide being least reactive........... so it should discharge in preference to halogens

 

[papajohn]

i do know about preferential discharge but i thought the series for anions was

OH- I- Br- Cl- NO3- SO4-2 F-

with hydroxide being least reactive........... so it should discharge in preference to halogens

But it also depend on these:
Concentration of ion
Nature of electrode

 

[mohdumar]

But it also depend on these:
Concentration of ion
Nature of electrode

the question in past papers simply said "Aqueos KBr" how am I supposed to know its conc. and exam report also said that most candidates got this ques wrong so whose faullt..........???

 

[Queens]

the question in past papers simply said "Aqueos KBr" how am I supposed to know its conc. and exam report also said that most candidates got this ques wrong so whose faullt..........???

When the question doesnot mention whether the solution is dilute or concentrated ; assume it to be concentrated.

This is a rule made by CIE.

 

[Queens]

Dont worry people its good u get ur mistakes now or else it will be a really hard lesson to learn, keep revising chemistry,bio and physics at least fortnightly you will eventually even start remembering the minor details and dont rote learn please try understanding it will even come good in A Levels

That was trully beautiful . Many people will be inspired by it.

 

[mohdumar]

When the question doesnot mention whether the solution is dilute or concentrated ; assume it to be concentrated.

This is a rule made by CIE.

hey thanks for the tip

 

[scouserlfc]

i guess v have to assume it as dilute! :-/ cx cncntrated gives the same result as molten! so if aqueous is given, it shld b taken as dilute

Nopes it supposed to be concentrated if u still are confused check the answer for a CIE question on Electrolysis where they say the products on anode when aqueous NaCl is electrolysed,its bound to be Cl2 and not O2 !