Physics, Chemistry and Biology: Post your doubts here!

[Princess Raven]

Yes, the same rule applies with noble metals such as Platinum,Silver,Gold or those quite low in the reactivity series!
If they are high in the series, yes u can definitely prepare a salt, However metals such as Sodium and Potassium will result in a Very Dangerous Reaction!
Only M.A.Z.I.T metals (Magnesium, Aluminum, Zinc, Iron, Tin) are most suitable!

thanks!! oh just one more question could u tell me the equlibrium equation that occurs during melting??? and how do we make 1-chloropropane from propane? is it substitution rxn? THANKS!!

 

[Princess Raven]

Could anybody explain to me why when we use step up transformer the current is reduced so we use thinner and lighter cable ? i can't get what the relation between the current and the cables.

I dont know where u got that from but i dont think we need to know the relation.. u just need to know that step up transformers reduces current and how we can prevent to much energy lost.. there are many ways.. like using thick copper wires to reduce heat loss or use an iron core

 

[Princess Raven]

Hi guys,
Please help me to check out my answers for Paper 3 chemistry May/June 2012 and give me your feedback so I can improve my answers in the coming papers.

My worked paper can be grabbed from : https://www.yousendit.com/download/UVJpSkhVNkduSlFVV01UQw

Cheers

first in q 1 c (i) id suggest u say they react with water vapour not water alone.. then q 4 part b ur third reason seems to be incorrect transition metals are always hard and strong never say soft.. then q 5 b (i) copper metal is incorrect its copper oxide and the balancing of 5 b ii is incorrect also. then q 8 part a ii the answer is totally wrong its electrode b u have to always check the electron flow which is shown in the diagram.. Thats all GOOD LUCK for ur exam..

 

[Sam Ivashkov]

Hi, I need some help. Its a confusion actually.
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s09_qp_6.pdf
For Question number 2 (d) (iii), how is the answer 22.5? (Says the mark scheme) Are they saying that a rise in temperature indicates that a neutralization reaction has taken place and that increasing the volume of HCL only increases the the temperature but doesn't do anything specific to the reaction itself?

 

[haidi]

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.

hello could you please help me in Q2 (a) http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w05_qp_6.pdf plzzzzz

 

[Princess Raven]

can any one help me
with w08 chemistry paper 3 Q7

for p31? part a volume of o2 left just use the mole ratio 1: 6.5 and thus 10: x then cross multiply u get 65 but since they want how much is left we do 100-65 which will give u 35. and the same goes for the next 1:4 thus 10:x cross multiply and get 40cm3

 

[Princess Raven]

Hi, I need some help. Its a confusion actually.
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s09_qp_6.pdf
For Question number 2 (d) (iii), how is the answer 22.5? (Says the mark scheme) Are they saying that a rise in temperature indicates that a neutralization reaction has taken place and that increasing the volume of HCL only increases the the temperature but doesn't do anything specific to the reaction itself?

its just the point where they intersect.. which is 22.5

 

[CaveDweller65]

thanks!! oh just one more question could u tell me the equlibrium equation that occurs during melting??? and how do we make 1-chloropropane from propane? is it substitution rxn? THANKS!!

It probably is a sub. reaction! I'm not really sure but i guess it's just like methane!
Equilibrium?!?! I need some help on that myself

 

[CaveDweller65]

Hey Guys!! I really need some help with this one.. Q.3 (c)
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w10_qp_61.pdf

 

[mak kings]

We know that R = ρL/A
Since the diameter of the second wire(d2) is half the diameter of the first wire (d1), the area of the second wire(A2) is one fourth the area of the first wire(A1)
[as area = pi * (d/2)^2 ie pi *r^2]
So, R2 = (0.45/0.3) * R1
ρL2/(A1/4) = (0.45/0.3) * (ρL1/A1)
on solving, the two ρ n the A1 cancel each other out.
We get, 4L2 = 1.5 * L1
L2 = (1.5/4) * L1
L2 = 0.375 * L1
L2 = 37.5 % of L1
Hope u gt it!!

THNX ALOT !!!

 

[Princess Raven]

lol

It probably is a sub. reaction! I'm not really sure but i guess it's just like methane!
Equilibrium?!?! I need some help on that myself

IKR there was a question in w12 v32 it was sooo weird..but anyhow ya i think its sublimation THANKS alot for ur help!!!!!

 

[Henry Smith]

first in q 1 c (i) id suggest u say they react with water vapour not water alone.. then q 4 part b ur third reason seems to be incorrect transition metals are always hard and strong never say soft.. then q 5 b (i) copper metal is incorrect its copper oxide and the balancing of 5 b ii is incorrect also. then q 8 part a ii the answer is totally wrong its electrode b u have to always check the electron flow which is shown in the diagram.. Thats all GOOD LUCK for ur exam..

Hi Raven,

For Q.1c, actually acidic fumes react with water vapour and rain water on the way down , you still get mark if you mention water, more information can be found at http://www.umac.org/ocp/HowisAcidRainFormed/info.html

For Q.4b : I know that in the MS they says transition metals all should be hard or intensively hard that why they are used for making alloys, more about Vanadium at http://chemistry.about.com/od/elementfacts/a/vanadium.htm.

For Q.5b(i) was my mistake, thanks for pointing it out.

For Q.5b(ii), Numbers were jumping around, I forgot to delete the coefficient, editing pdf file is a painful job. Appreciate, Raven.

For Q.8a(ii): My mistake again, always rush as time is running out. In a simple cell, electrons flow from the more reactive metal, it is the negative pole. Electrons flow away from B so B dissolves. This is the reason why, Zn is used to protect ships from rusting. Again, the text-boxes jump around the page. For sure you have checked the MS...hihi..

Thanks very indeed, I'm a mickey mouse chemist who never had chance to take GCSE exams. I studied a different system. I graduated from a university 12 years ago. I just wanted to do some sample answers for a boy whose family lives next to me.

 

[Mariam879]

Hi guys,
Please help me to check out my answers for Paper 3 chemistry May/June 2012 and give me your feedback so I can improve my answers in the coming papers.

My worked paper can be grabbed from : https://www.yousendit.com/download/UVJpSkhVNkduSlFVV01UQw

Cheers

That was very helpful thankssssssssss alooooot and btw you can just write it with pen and paper, scan it , then post it

 

[Henry Smith]

That was very helpful thankssssssssss alooooot and btw you can just write it with pen and paper, scan it , then post it

It's my pleasure Maria, just do it for fun, I'll step into bio and physics. I have done some AS chemistry papers as well, will find some time to upload.

Please my corrected version of the previous paper bellow that Raven has pointed out some mistakes early on.

https://www.yousendit.com/download/UVJpSkhaTlFRYS80WjlVag

 

[SanadN]

An important chemistry problem !!!!
in extraction of zinc , they say it can be done by both ; reduction by carbon or electrolysis.
but in electrolysis, hydrogen is less reactive than zinc , so it is the one who is supposed to be discharged, instead, they say that zinc is deposited at the cathode.
can somebody help me please because this is so confusing??!!
thanks.

 

[asma tareen]

if we use molten compound than zinc would be depostied cux no hydogen ions would be there

 

[Princess Raven]

Hi Raven,

For Q.1c, actually acidic fumes react with water vapour and rain water on the way down , you still get mark if you mention water, more information can be found at http://www.umac.org/ocp/HowisAcidRainFormed/info.html

For Q.4b : I know that in the MS they says transition metals all should be hard or intensively hard that why they are used for making alloys, more about Vanadium at http://chemistry.about.com/od/elementfacts/a/vanadium.htm.

For Q.5b(i) was my mistake, thanks for pointing it out.

For Q.5b(ii), Numbers were jumping around, I forgot to delete the coefficient, editing pdf file is a painful job. Appreciate, Raven.

For Q.8a(ii): My mistake again, always rush as time is running out. In a simple cell, electrons flow from the more reactive metal, it is the negative pole. Electrons flow away from B so B dissolves. This is the reason why, Zn is used to protect ships from rusting. Again, the text-boxes jump around the page. For sure you have checked the MS...hihi..

Thanks very indeed, I'm a mickey mouse chemist who never had chance to take GCSE exams. I studied a different system. I graduated from a university 12 years ago. I just wanted to do some sample answers for a boy whose family lives next to me.

No problem! just wanted to ensure ppl dont get confused lol.. and thats really helpful for the boy! insA he will do well!

 

[Princess Raven]

An important chemistry problem !!!!
in extraction of zinc , they say it can be done by both ; reduction by carbon or electrolysis.
but in electrolysis, hydrogen is less reactive than zinc , so it is the one who is supposed to be discharged, instead, they say that zinc is deposited at the cathode.
can somebody help me please because this is so confusing??!!
thanks.

i think it cant be done by electrolysis because its lower than carbon in the reactivity series.. it can only be done by the reduction of its oxide by carbon!

 

[SanadN]

if we use molten compound than zinc would be depostied cux no hydogen ions would be there

but they say it is dissolved in a diluted solution of H2SO4 , which when reacting with zinc oxide, produces both zinc sulfate and water, therefore water is present , and H2 must be discharged.

 

[asma tareen]

but they say it is dissolved in a diluted solution of H2SO4 , which when reacting with zinc oxide, produces both zinc sulfate and water, therefore water is present , and H2 must be discharged.

look molten zinc salt will be used ok it can be zinc chloride and when a compound is melted its in liquid state so no need to disslove in water