Chemistry: Post your doubts here!

[Malik777]

Anyone having AS Summarised Notes for Chem ? Plz I utterly need :/

 

[unseen95]

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

thanks man

 

[Silent Hunter]

In chem paper 5 : how many sf or dp should we give our answers in, in plotting the points for the graphs in question number 2?

(any link to paper 5 revisions?)

JazakAllah

 

[littlecloud11]

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

Are you sure the answer is N2O4?
I get N2O2
No of moles of HCl = 200/1000 * 1 = .2
1 mol HCl reacts with 1 mol NH3 so there was .2 mol NH3 present. 1 mol NH3 has 1 mol N atoms. So, .2 mol NH3 has .2 mol N atoms
.1 mol NxOy was burned and that resulted in .2 mol N atoms in ammonia. so 1 mol NxOy had .2/.1= 2 mol N, so x=2
.2 mol NH3 weighs= .2*17 =3.4g
total product mass = 7.2, so mass of water produced is 7.2- 3.4= 3.8g
3.8g H2O = .21 mols Hence .2 mols of O atoms was present in .1 mol of NxOy. So 1 mol NxOy had 2 mol O. y=2
The formula should have been N2O2

Unless I'm missing something here....?

 

[Tkp]

its better to give in 1 dp

In chem paper 5 : how many sf or dp should we give our answers in, in plotting the points for the graphs in question number 2?

(any link to paper 5 revisions?)

JazakAllah

 

[snowbrood]

Are you sure the answer is N2O4?
I get N2O2
No of moles of HCl = 200/1000 * 1 = .2
1 mol HCl reacts with 1 mol NH3 so there was .2 mol NH3 present. 1 mol NH3 has 1 mol N atoms. So, .2 mol NH3 has .2 mol N atoms
.1 mol NxOy was burned and that resulted in .2 mol N atoms in ammonia. so 1 mol NxOy had .2/.1= 2 mol N, so x=2
.2 mol NH3 weighs= .2*17 =3.4g
total product mass = 7.2, so mass of water produced is 7.2- 3.4= 3.8g
3.8g H2O = .21 mols Hence .2 mols of O atoms was present in .1 mol of NxOy. So 1 mol NxOy had 2 mol O. y=2
The formula should have been N2O2

Unless I'm missing something here....?

well i have already solved this will give u an explanation for this when i get free

 

[examkiller]

J03. 2c paper 3 chem !!
PLease help with moles

Each tablet contains the same number of moles of CaCO3 and MgCO3. One tablet reacted with excess hydrochloric acid to produce 0.24 dm3 of carbon dioxide at r.t.p.
For Examiner’s Use
CaCO3 + 2HCl → CaCl2 + CO2 + H2O MgCO3 + 2HCl → MgCl2 + CO2 + H2O
(i)Calculate how many moles of CaCO3 there are in one tablet.
number of moles CO2=
number of moles of CaCO3 and MgCO3 =
number of moles of CaCO3=
.............. .............. ..............
(ii)Calculate the volume of hydrochloric acid, 1.0 mol / dm3, needed to react with one tablet.
number of moles of CaCO3 and MgCO3 in one tablet=
Use your answer to (c)(i).
number of moles of HCl needed to react with one tablet =
volume of hydrochloric acid, 1.0 mol / dm3, needed to react with one tablet=
.............. .............. ..............
[2]


http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_3.pdf

 

[Mr.Sir]

Salams
Some help on transition metals needed here..can someone give me a link or something to understand parts (k) (l) and (m) from the syllabus content on transition metals..page 28
Or if they can explain it to me themselves plz?

 

[Mr.Sir]

Re: All Chemistry help here!! Stuck somewhere? Ask here!


Salams
Some help on transition metals needed here..can someone give me a link or something to understand parts (k) (l) and (m) from the syllabus content on transition metals..page 28
Or if they can explain it to me themselves plz?

 

[darknessinme]

Salams
Some help on transition metals needed here..can someone give me a link or something to understand parts (k) (l) and (m) from the syllabus content on transition metals..page 28
Or if they can explain it to me themselves plz?

http://www.chemguide.co.uk/CIE/

 

[Ahmedraza73]

An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with −MnO4/ H+.
What is the least number of carbon atoms such an alcohol could possess?
A 5 B 6 C 7 D 8

 

[Ahmedraza73]

Guyz please help me with question number 25 and 34.
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
Please help someone?

 

[Mr.Sir]

http://www.chemguide.co.uk/CIE/

U sir, are a Legend!

 

[Mr.Sir]

Ple

http://www.chemguide.co.uk/CIE/

please tell me that there is also a physics guide similar to this one....please!

 

[blabla]

CHEM P5 QUESTION!

In an experiment, if we are to thermally decompose a solid and collect and measure the gas evolved, how do i shake the test tube/conical flask/whatever that contains the solid to distribute the heat evenly? Since it's kinda attached to the gas syringe and shaking it isn't really possible.

Secondly, should i use a conical flask or a test tube attached to the clamp and stand? Is the conical flask resistant to high temperatures?

 

[Mr.Sir]

CHEM P5 QUESTION!

In an experiment, if we are to thermally decompose a solid and collect and measure the gas evolved, how do i shake the test tube/conical flask/whatever that contains the solid to distribute the heat evenly? Since it's kinda attached to the gas syringe and shaking it isn't really possible.

Secondly, should i use a conical flask or a test tube attached to the clamp and stand? Is the conical flask resistant to high temperatures?

If u r heating a solution to collect gas use a conical flask..otherwise usethe testube if its a solid.
Make sure not to touch the base of the conical flask with the flame..and use a gauze on the tripod stand to reduce direct contact of the flame..rest safety is assured!
Plus..I don't think u need to shake the conical flask or something..the gas will automatically make space.

 

[darknessinme]

Ple
please tell me that there is also a physics guide similar to this one....please!

i haven't found any decent websites on physics like chemguide.
try http://www.chemguide.co.uk/qandc/physbio.html#top or youtube

 

[Ahmedraza73]

Guyz please help me with question number 25 and 34.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
Please help someone?

Please someone answer my question littlecloud11 or anyone else

 

[Muhammad Bin Anis]

Please someone answer my question littlecloud11 or anyone else

the answer for 25 should be C
and 34 should be D

solving 25 requires you to learn organic chemistry reactions

as far as 34 is concerned, you need to consider that the temperature increases, so an endothermic reaction will be favoured for any equlibrium mixtures.
in option 1, that endothermic reaction results in two moles of products from one mole of reactant.(hence an inc. in pressure)
option 2 does not have any effect because the number of moles are same.(no change in pressure exerted)
option 3 will also not have any effect because using nitrogen on both sides will not change the pressure (same pressure from both sides so the mercury remains level in between)

 

[salvatore]

Guyz please help me with question number 25 and 34.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
Please help someone?

The answer for qn. 25 is C.
To convert a halogenoalkane to a nitrile, we need to react it with cyanide ions (Usually potassium cyanide, KCN, in ehtanol). So X is solved.
Hydrolysis is used to convert a nitrile into a carboxylic acid. So, by reacting the butanitrile with dilute HCL, the carbon-nitrogen triple bond is broken down by water to form butanoic acid.

Hope qn 34 is made clear by the other person