Chemistry: Post your doubts here!

[daredevil]

Down the group the oxidising ability increase, thus down the group the better reducing agents.

Ummm i seriously think u're wrong abt that bcz. If it has a high oxidising ability it means that it oxidises well means its a good oxidising agent. So dont say that down the group are better reducing aggents bcz technically they r just poor oxidising agents. Link it with the electron give take concept of redox or it will bw confusing.
E.g there r bad conductors and good conductors and then there r insulators. U cant say that relatively poor conductors are insulators. Just keep to the basic concept bcz chem is confusing enough as it is right??
I hope u all get it now Rahma Abdelrahman

 

[PhyZac]

Ummm i seriously think u're wrong abt that bcz. If it has a high oxidising ability it means that it oxidises well means its a good oxidising agent. So dont say that down the group are better reducing aggents bcz technically they r just poor oxidising agents. Link it with the electron give take concept of redox or it will bw confusing.
E.g there r bad conductors and good conductors and then there r insulators. U cant say that relatively poor conductors are insulators. Just keep to the basic concept bcz chem is confusing enough as it is right??
I hope u all get it now Rahma Abdelrahman

I can't argue, I am not a knowledgeable person on this topic, I just told what I have learned and found in many books and site.

 

[daredevil]

I can't argue, I am not a knowledgeable person on this topic, I just told what I have learned and found in many books and site.

Maybe ure ryt i just said wat i understood. Let the others decide ryt

 

[jinjanet]

It's definitely B.

The only one out of those which can get Oxidized are B and C.. since it didn't decolourize Br2 it doesn't have a C=C double bond so it's not ethene. Answer is B.

i thought bromine and ethanol will react to form bromoethane?and so color of bromine water will be decolorised?
http://wiki.answers.com/Q/What_happens_when_bromine_water_is_added_to_ethanol

 

[syed1995]

i thought bromine and ethanol will react to form bromoethane?and so color of bromine water will be decolorised?
http://wiki.answers.com/Q/What_happens_when_bromine_water_is_added_to_ethanol

That page is incorrect. Find me a page with a equation C2H50H + Br2. cause that reaction doesn't occur.. at least not the addition reaction of bromine which is in our course.

The addition of bromine only occurs with unsaturated compounds (those with double/triple bonds). And ethanol is a saturated compound. So no addition reaction of bromine occurs.

The Substitution reaction of Ethanol is with HBr .. C2H5OH + HBr ---> C2H5Br + H20

 

[lyuchenqujoy]

mj/08 qp1
question 27: please tell me how to judge between the answer C&D
question 38: please tell me what happens during these process
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

Thx a lot!!!!

Can anyone answer my questions PLEASE!!!! TAT..

 

[Nabeel.Ahmad]

Chemistry is Soooo Easyy!

 

[Raiyan3]

Please explain question 6
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

And question 3 and 7
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

 

[PhyZac]

i thought bromine and ethanol will react to form bromoethane?and so color of bromine water will be decolorised?
http://wiki.answers.com/Q/What_happens_when_bromine_water_is_added_to_ethanol

syed1995 have answered your question, but I want to mention a point, i.e. NEVER use such sites for your learning! It is answered by people who may not be knowledgeable enough.

 

[aalmuhannadi]

0.144g of an aluminium compound X react with an excess of water, to produce a gas. This gas burns completely in O2 to form H2O and 72cm^3 of CO2 only. The volume of CO2 was measured at room temperature and pressure, what could be the formula of X?
A: Al2C3 B: Al3C4 C: Al4C3 D: Al5C3

My teacher explained this question to me once but I cannot find his method. Can anyone explain how to do this question WITHOUT having to use any sort of chemical equation? I remember the first step was to find the number of moles of carbon, which is 0.072/24 = 0.003 moles, but what are the steps after that?

 

[afsah shaikh]

Two moles of compound P were placed in a vessel. The compound P was partly decomposed by
heating. A dynamic equilibrium between chemicals P, Q and R was established.
At equilibrium, x mol of R were present and the total number of moles present was (2 + x).
What is the equation for this equilibrium?
A P ---> 2Q + R
B 2P---> 2Q + R
C 2P---> Q + R
D 2P----> Q + 2R

A farmer spreads lime on land which has already been treated with an ammonium nitrate
fertiliser.
Which reactions will occur in the treated soil?
1 Ca(OH)2 + 2NH4+(aq) → Ca2+(aq) + 2NH3 + 2H2O
2 Ca(OH)2 + 2H+(aq) → Ca2+(aq) + 2H2O
3 Ca(OH)2 + CO2→ CaCO3 + H2O

the first one is a single choice question while the next one you have to tell which statement is correct, can someone help plzzz..

 

[daredevil]

Chemistry questions
O/N 2011 p12
Questions:
7 9 10 18 24 26 31 34 37 38 39 40

Please help me. It seems like i know nothing of chemistry watsoever

 

[daredevil]

Why do we all have to study sooo harddd :O i feel like pulling my hair out >:0

 

[yousef]

littlecloud11
To Identify oxide of nitrogen 0.1 mol of oxide is mixed with an excess of hydrogen and passed over a catalyst at suitable temperature
NxOy + H2 on heating with catalyst gives xNH3 +yH2O
the produced weighs 7.2g the ammonia produced is neutralized by 200cm^3 of 1.0 moldm^-3 Hcl
what is the formula of the oxide of nitrogen
tell me why the answer is N2O4

Ummm i seriously think u're wrong abt that bcz. If it has a high oxidising ability it means that it oxidises well means its a good oxidising agent. So dont say that down the group are better reducing aggents bcz technically they r just poor oxidising agents. Link it with the electron give take concept of redox or it will bw confusing.
E.g there r bad conductors and good conductors and then there r insulators. U cant say that relatively poor conductors are insulators. Just keep to the basic concept bcz chem is confusing enough as it is right??
I hope u all get it now Rahma Abdelrahman

salam ... can any one plz answer the first question for this year ... i started with this and i really got disappointed with my fist quetion in the first paper >>>http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s03_qp_2.pdf qp1 ??

 

[unseen95]

please help me out with an explanation for question number 7. http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

 

[lyuchenqujoy]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

quetion 27
the answer is A
please explain what happens here..

 

[PhyZac]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

quetion 27
the answer is A
please explain what happens here..

that chemical has 2 functional groups, ester and alkene

Hydrolysis of ester occur by addition of acid (or alkaline) so they warmed sulfuric acid, the ester bond breaks. (forming carboxylic acid and alcohol)
then addition of hydrogen in presence of catalyst with open double bonds (alkene ) to make alkane.

 

[leosco1995]

The solubility product of PbCrO4 is 1.69 x 10^-14 mol^2 dm^-6.

Concentrated aqueous lead(II) nitrate is added drop wise to 0.010 mol dm^-3 potassium dichromate(VI). What is the concentration of lead (II) ions when the first trace of precipitate appears?

 

[aalmuhannadi]

please help me out with an explanation for question number 7. http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

A: Aluminium has metallic bonds and phosphorus has covalent bonds
B: Chlroine has covalent bonds and argon has no bonding (or van der waals force if you want to consider that)
C: Magnesium is metallic and silicon is covalent
D: Sulfur and chlorine both have only covalent bonds

So it's D

 

[scouserlfc]

salam ... can any one plz answer the first question for this year ... i started with this and i really got disappointed with my fist quetion in the first paper >>>http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s03_qp_2.pdf qp1 ??

Here it goes !
Isotope definition is supposed to be written here refer to your books or use your brain or maybe just write an atom with same electrons and protons but different number of neutrons

for peak at 35 35Cl is responsible for it
for peak at 38 ,H and 37 Cl are responsible that is HCl (with Cls nucleons = 37 )

As it tells u to look at the peaks to decide the ratio of the two Cl isotopes then look at the peaks at 35 and 37 only as they contain Cl only
the relative abundance of 35 peak is about 30 and for the peak at 37 it is abt 10
now just do this
35Cl : 37Cl
30 : 10
3 : 1
so thats the ratio !

so we know that they exist in the ratio 3:1 so now use the idea that these isotopes are the only Cl isotopes so their total abundance equals to as seen in the graph 40 and do this working
((3(35) + 1(37))/40) * 100
35.5 is the answer !