Physics, Chemistry and Biology: Post your doubts here!

[yousawinner]

Actually in crystallization we cool the solution to get the crystals but in evaporation, we heat it to separate the liquid. Like an example: in making of silicon chips we use crystallization method cuz if we would use evaporation it would damage it!!1

Just to be on the right page, crystallization occurs when mixing two insoluble salts to make a soluble one, right?

 

[Saahil Parikh]

can someone post notes for electromagnetism..mainly motors and generators..plz..thnk u

 

[ahmedali1]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s09_qp_3.pdf
qouestion 4
how do we draw the parallelogram ?????????????

 

[haidi]

could you please give me an exact information considering kinetic theroy plzzzzzzzzzzzzzzzz

Assalam-o-Alaikum.
Post your Physics, Chemistry and Biology doubts in here and members, along with me will try there best to help you out.

 

[catwong]

Biology Essay or Structured questions :
When ask to do comparison of either similiarity or difference, can we make a table to group the answers according to same category???
Basically, can we draw a line in between the answer space ??

 

[Albus Dumbledore]

Please help me. Chemistry qp 32 winter 2011. I don't understand what exactly question 6(c) is asking. Please help me, I've got an exam tomorrow and I don't understand it at all!!

 

[franklin2012]

please someone help me out at electrolysis i dont get any of it i mean how to form ionic equations and all i just dont get it explain me wht it is and if u can give me a site where i can get notes on it please its urgent thank u
and please explain the question 6 c1 cii and ciii in detail if u can please of http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s06_qp_3.pdf

 

[Rahma Abdelrahman]

please someone help me out at electrolysis i dont get any of it i mean how to form ionic equations and all i just dont get it explain me wht it is and if u can give me a site where i can get notes on it please its urgent thank u
and please explain the question 6 c1 cii and ciii in detail if u can please of http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s06_qp_3.pdf

Sorry I can't remember all about electrolysis (I finished in JUNE) (u can ask specific questions if u want bec. it is a bit lengthy topic ) but i think i can help u out in those Qs..
6 c i --> A reductant ( or reducing agent ) is the substance that is oxidised, Oxidation is the loss of electrons .. in a simple cell, electrons move from the more to the less reactive metal, so here from Zn to Fe, which means Zn loses electrons, is oxidised and hence is the reductant (here you have to mention "Zinc atoms" or Zn electrode , and they mention "bubbles of hydrogen atoms" at the iron electrode, which means that hydrogen ions from the electrlyte (H2SO4) gains the electrons that zinc loses so the oxidant is "Hydrogen ions".
ii) Here you should use two metals that further away from each other in the rectivity series than iron is with Zinc, but you can't mention that only, u must say the names of the metals for example u can say, " Use Aluminium instead of zinc as the electrode" or "use lead instead of iron" i e u should choose a metal less reactive than iron or a metal that is more reactive than Zinc or both.. but mentioning the metals' names is essential.
iii) answer is sacrificial protection or stop iron/steel rusting or galvanisation: I think this depends on ur memorisation .. but u say galvanisation only bec. there is a zinc electrode..
Any more doubts?

 

[french410]

why does calcium displace aluminum in aluminum chloride? plzz help

 

[Iridescent]

why does calcium displace aluminum in aluminum chloride? plzz help

This is because calcium is higher than aluminium in the reactivity series i.e., it is more reactive than aluminium thus it replaces aluminium from its salt

 

[franklin2012]

Sorry I can't remember all about electrolysis (I finished in JUNE) (u can ask specific questions if u want bec. it is a bit lengthy topic ) but i think i can help u out in those Qs..
6 c i --> A reductant ( or reducing agent ) is the substance that is oxidised, Oxidation is the loss of electrons .. in a simple cell, electrons move from the more to the less reactive metal, so here from Zn to Fe, which means Zn loses electrons, is oxidised and hence is the reductant (here you have to mention "Zinc atoms" or Zn electrode , and they mention "bubbles of hydrogen atoms" at the iron electrode, which means that hydrogen ions from the electrlyte (H2SO4) gains the electrons that zinc loses so the oxidant is "Hydrogen ions".
ii) Here you should use two metals that further away from each other in the rectivity series than iron is with Zinc, but you can't mention that only, u must say the names of the metals for example u can say, " Use Aluminium instead of zinc as the electrode" or "use lead instead of iron" i e u should choose a metal less reactive than iron or a metal that is more reactive than Zinc or both.. but mentioning the metals' names is essential.
iii) answer is sacrificial protection or stop iron/steel rusting or galvanisation: I think this depends on ur memorisation .. but u say galvanisation only bec. there is a zinc electrode..
Any more doubts?

thanks so much so much for help

 

[Rahma Abdelrahman]

thanks so much so much for help

u r wlc.
Any more doubts, please ask..

 

[franklin2012]

please someone help me out in http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Biology (0610)/0610_s07_qp_2.pdf question 4 a iv) please explain i think answer is F but the correct answer is D please explain

 

[Rahma Abdelrahman]

please someone help me out in http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Biology (0610)/0610_s07_qp_2.pdf question 4 a iv) please explain i think answer is F but the correct answer is D please explain

Yeah.. D
if u compare the "area destroyed each year 1990 – 2000 " with the "area of forest in 2000" u will find that for D, 2000 approx. 1.7% of the 117000 while 84000 is approx. 1% of the 8399000, meaning that D decreases at a faster rate ,in addition to the original no. being much less in D

 

[franklin2012]

u are

Yeah.. D
if u compare the "area destroyed each year 1990 – 2000 " with the "area of forest in 2000" u will find that for D, 2000 approx. 1.7% of the 117000 while 84000 is approx. 1% of the 8399000, meaning that D decreases at a faster rate ,in addition to the original no. being much less in D

brilliant thanks a lot

 

[Rahma Abdelrahman]

u are

brilliant thanks a lot

oh..
thanx..
You are welcome as well

 

[franklin2012]

oh..
thanx..
You are welcome as well

u get A*right?

 

[Rahma Abdelrahman]

u get A*right?

yup.. alhamdulillah
wbu? u r going 4 nov. session ryt?

 

[franklin2012]

yeah i am going for it and i really weak at studies (thats what i think )

 

[Rahma Abdelrahman]

and so i am very tensed

Don't worry Just do your best .. and be satisfied with ur effort in the end.. this is more imp. than getting high grades, (not saying that 's not important )
Stress would help u in no way bro