Biology; Chemistry; Physics: Post your doubts here!

[GetSomeLife]

Ok relax people... i think i cleared the misconception that there ain't such a thing
Back to topic people

Fibre-optic cables are sometimes used to carry out internal examinations on the human stomach.
Suggest one reason why the cable is made of thousands of very thin optical fibres.

Thanks in advance.

 

[SalmanPakRocks]

what would be the product? i saw a question asking for equation of Al2O3 + CaO

Was this in the past papers? Because when I googled it, it came under the heading of thermodynamic.

 

[ashiqbal]

Ok relax people... i think i cleared the misconception that there ain't such a thing
Back to topic people

Fibre-optic cables are sometimes used to carry out internal examinations on the human stomach.
Suggest one reason why the cable is made of thousands of very thin optical fibres.

Thanks in advance.

to get many images of the internal structure/better quality of image.

 

[ashiqbal]

Was this in the past papers? Because when I googled it, it came under the heading of thermodynamic.

Oh Bhains!! but i really saw this. ill try to post year

 

[SalmanPakRocks]

Oh Bhains!! but i really saw this. ill try to post year

Yes Please do, because I have solved almost 10 years papers now and I haven't seen any kind of reaction like this yet, if my memory doesn't decieve me.

 

[SalmanPakRocks]

http://www.xtremepapers.com/papers/...onal O Level/Physics (5054)/5054_w09_qp_2.pdf
I need help in Question 7 part a.

 

[étudiante]

That's my query, if they don't mention that the solution is dilute or concentrated, then we have to take it as dilute, but here it is taken as concentrated!

what i am asking is that are you guys sure that there is an error in the ms and in our exam we have to take aqueous sodium chloride(only) as dilute if not specified?

the mark scheme isnt wrong...
it is taken as dilute and Cl2 is discharged preferentially to O2... the reason for this is that there is a discharge series (rather like a reactivity series) which helps us to decide which ion will be discharged... u can basically remember that Cl2 is quite high in the series so it is always discharged when present

 

[ashiqbal]

Yes Please do, because I have solved almost 10 years papers now and I haven't seen any kind of reaction like this yet, if my memory doesn't decieve me.

w11_qp21 Q7. this paper was exceptionally difficult!

 

[SalmanPakRocks]

w11_qp21 Q7. this paper was exceptionally difficult!

For Chemistry or Physics?

 

[ashiqbal]

the mark scheme isnt wrong...
it is taken as dilute and Cl2 is discharged preferentially to O2... the reason for this is that there is a discharge series (rather like a reactivity series) which helps us to decide which ion will be discharged... u can basically remember that Cl2 is quite high in the series so it is always discharged when present

actually OH- is higher in the discharge series than Cl-, and Cl- is discharged only when the concentration of Cl- ions is much greater than OH- ions (ie in a conc. NaCl solution!)

 

[ashiqbal]

For Chemistry or Physics?

chem. it is the question of amphoteric oxide, and it was very difficult!

 

[étudiante]

actually OH- is higher in the discharge series than Cl-, and Cl- is discharged only when the concentration of Cl- ions is much greater than OH- ions (ie in a conc. NaCl solution!)

the water is not going to ionise in dis case... there wont be any OH- ions because there is no acid to promote ionisation (there will be a ver small quantity acctually) so effectively its the Cl- ions which are in excess compared to OH-

 

[SalmanPakRocks]

I guess it's Question 8 that has this
Al2O3 + 2NaOH = 2NaAlO2 + H2O
Aluminium can't be reduced by chemical reduction remember?

 

[ayeshaK]

http://www.xtremepapers.com/papers/...onal O Level/Physics (5054)/5054_w09_qp_2.pdf
I need help in Question 7 part a.

Its 1
3/2 to find the centre of maas which is 1.5 then 2.5 - 1.5 gives u the answer 1

 

[SalmanPakRocks]

Its 1
3/2 to find the centre of maas which is 1.5 then 2.5 - 1.5 gives u the answer 1

Yeah I got this, but why should we do this?

 

[beeloooo]

yup same question y should we do dis ??

 

[GetSomeLife]

Yeah I got this, but why should we do this?

Because they asked you to and also you'll need it later

the water is not going to ionise in dis case... there wont be any OH- ions because there is no acid to promote ionisation (there will be a ver small quantity acctually) so effectively its the Cl- ions which are in excess compared to OH-

Yes but they didn't mention that it is concentrated... and in that case it is to be taken as dilute and OH- ions should be discharged... the ms is confusing =/

 

[SalmanPakRocks]

Because they asked you to

I was talking about the method
Why should this be done, the logic behind it

 

[étudiante]

Because they asked you to


Yes but they didn't mention that it is concentrated... and in that case it is to be taken as dilute and OH- ions should be discharged... the ms is confusing =/

dere ARE NO OH- ions in dat solution becuse water will not ionise in prescence of a salt! Cl- is the (majorly) the anion present dere...

(OH- ions will be VERY low in conc... negligible really)

 

[GetSomeLife]

I was talking about the method
Why should this be done, the logic behind it

Solve the question... you'll need this info later when finding the downward force

dere ARE NO OH- ions in dat solution becuse water will not ionise in prescence of a salt! Cl- is the (majorly) the anion present dere...

how do you know that Cl- ions are in a majority?