Chemistry: Post your doubts here!

[smzimran]

people wat to prepare fr while studyng fr p5?? should we jst go thru the syllabus nd solve past papers???

there's a chem p5 tips thread too.. read that too.

http://www.xtremepapers.com/community/threads/chemo-p5-tips.5917/

 

[Hassi123]

platinum, NOT palladium.....just yesturday i saw this written in a mark scheme

palladium is also accepted bro

 

[Soulgamer]

Do we need to know the working of mass spectrometer?

 

[farhan143]

Assalamwa'laikum Warahmatullahi Wa Baraqaatuhu...

I AM GIVING CHEM P21 THIS COMING 21st
I am giving AS levels...

i have question it does not involve past paper though....

1. Construct ionic half equation for:
a) PbO2(s) being reduced to PbSO4(s) in presence of of H2SO4(aq)
b) PbSO4(s) being reduced to Pb(s) in the presence of water.
c) Mow write the balanced equation for the reaction between PbO2 and lead in the presence of dilute sulfuric acid.

please someone EXPLAIN me the steps involved in getting the answer right...

THANK YOU!

 

[leosco1995]

Does the addition of HCN in the presence of NaCN to an aldehyde or ketone take place under room conditions or heat under reflux? My notes say the latter but the marking schemes say the former and I'm confused..

 

[Soulgamer]

It occurs at room temperature whereas hydrolysis of CN occurs with heat under reflux. Btw post link to marking scheme.

 

[Aahliya]

Hey anyone who can help me with P5 ??
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_52.pdf

Pls tell me how do you find solubility in Q2. (a) ??

 

[farhan143]

i am re-posting this question:

Assalamwa'laikum Warahmatullahi Wa Baraqaatuhu...

I AM GIVING CHEM P21 THIS COMING 21st
I am giving AS levels...

i have question it does not involve past paper though....

1. Construct ionic half equation for:
a) PbO2(s) being reduced to PbSO4(s) in presence of of H2SO4(aq)
b) PbSO4(s) being reduced to Pb(s) in the presence of water.
c) Mow write the balanced equation for the reaction between PbO2 and lead in the presence of dilute sulfuric acid.

please someone EXPLAIN me the steps involved in getting the answer right...

THANK YOU!

 

[angelicsuccubus]

i am re-posting this question:

Assalamwa'laikum Warahmatullahi Wa Baraqaatuhu...

I AM GIVING CHEM P21 THIS COMING 21st
I am giving AS levels...

i have question it does not involve past paper though....

1. Construct ionic half equation for:
a) PbO2(s) being reduced to PbSO4(s) in presence of of H2SO4(aq)
b) PbSO4(s) being reduced to Pb(s) in the presence of water.
c) Mow write the balanced equation for the reaction between PbO2 and lead in the presence of dilute sulfuric acid.

please someone EXPLAIN me the steps involved in getting the answer right...

THANK YOU!

hey.. umm they are all the same equations. Where did you find this question? and is it half equations that you're confused about?

 

[saudha]

1. do have to know the trends of the periodic table?
2. what do we actually study for chem p5?
3. if i solve pp is it enough??

 

[angelicsuccubus]

1. do have to know the trends of the periodic table?
2. what do we actually study for chem p5?
3. if i solve pp is it enough??

Check the guidelines in the syllabus too and check this:

http://www.xtremepapers.com/community/threads/chemo-p5-tips.5917/

 

[Jaf]

i am re-posting this question:
a) PbO2(s) being reduced to PbSO4(s) in presence of of H2SO4(aq)

I'm getting:
PbO2 + 4H^(+) + SO4^(2-) + 2e- ------> PbSO4 + 2H2O

This is a perfectly balanced half equation.
But the problem with this equation is that it doesn't make sense. Sulfuric acid is a dibasic acid. This means one mole of H2SO4 will give 2 moles of H+ and one moles of sulfate ions. But here, we have 4 moles of H+ and one moles of sulfate ions. Is such a reaction possible? I don't know.

 

[mr_perfect]

WHERE THE IS CHEM PAPER 4 THREAD ????? PAPER 4 CARRIES 38 % WEIGHTING MORE THAN ANY OTHER COMPONENT IN CHEMISTRY AND ALL PPL CARE ABOUT IS PAPER 5 AND PAPER 2. PAPER 5 CARRIES ONLY 23% WEIGHTING. IF ANY OF U KNOW WHETHER THERE IS ANY CHEM P4 THREAD PLEASE REPLY .
tnx

 

[angelicsuccubus]

I'm getting:
PbO2 + 4H^(+) + SO4^(2-) + 2e- ------> PbSO4 + 2H2O

This is a perfectly balanced half equation.
But the problem with this equation is that it doesn't make sense. Sulfuric acid is a dibasic acid. This means one mole of H2SO4 will give 2 moles of H+ and one moles of sulfate ions. But here, we have 4 moles of H+ and one moles of sulfate ions. Is such a reaction possible? I don't know.

Here: Take half equation from this
2 PbO2 + 2 H2SO4 = 2 H2O + O2 + 2PbSO4

 

[angelicsuccubus]

WHERE THE IS CHEM PAPER 4 THREAD ????? PAPER 4 CARRIES 38 % WEIGHTING MORE THAN ANY OTHER COMPONENT IN CHEMISTRY AND ALL PPL CARE ABOUT IS PAPER 5 AND PAPER 2. PAPER 5 CARRIES ONLY 23% WEIGHTING. IF ANY OF U KNOW WHETHER THERE IS ANY CHEM P4 THREAD PLEASE REPLY .
tnx

dude chill, okay? and if you wanna discuss chem p4, do it here.

 

[Jaf]

Here: Take half equation from this
2 PbO2 + 2 H2SO4 = 2 H2O + O2 + 2PbSO4

Oxygen? I don't think we're allowed to add oxygen. :S

 

[ibadsiddiqi]

November 2011 is so freakishly easy but the GT is so low..:-/

 

[angelicsuccubus]

Oxygen? I don't think we're allowed to add oxygen. :S

Im not adding it.. thats what happens

It's either the one with oxygen, or this one:
PbO2 + 2 H2SO4 = 2 H2O + Pb(SO4)2

 

[saudha]

Check the guidelines in the syllabus too and check this:

http://www.xtremepapers.com/community/threads/chemo-p5-tips.5917/

thank you

 

[oldfashionedgirl]

Do we need to know the working of mass spectrometer?

u need to know only how to perform its calculations.....there are a handful of questions related to its calculations in p1 and p2,esp p1