Chemistry: Post your doubts here!

[snowbrood]

Sweetjinnah i dont know how to tag lolz even i want to learn how to tag so do tell me if u ever figure it out

 

[snowbrood]

can u tell how 2 tag , plz.

write the name u want to tag for e.g snowbrood
and do write this code
[U S E R=1]Name[/U S E R ]
no spaces i am using this so that u can write this code

 

[snowbrood]

sweetjinnah

 

[daredevil]

can u tell how 2 tag , plz.

write @ and the person's name (don't type space) and wait for the options of names to appear just like it does on fb.. u might have to wait for a few seconds or so for the options to appear though...
snowbrood

happy taggging

 

[sweetjinnah]

write @ and the person's name (don't type space) and wait for the options of names to appear just like it does on fb.. u might have to wait for a few seconds or so for the options to appear though...
snowbrood

happy taggging

THANKS ALOT snowbrood and daredevil
u see i did that!!

 

[daredevil]

THANKS ALOT snowbrood and daredevil
u see i did that!!

np
hahahha... Yaay u

 

[snowbrood]

can anyone tell me how to determine which acid is stronger than the other using as concepts only.
for e.g write the correct order of strength of acid in increasing order for ethanoic acid chloroethanoic acid and phenol

 

[SIstudy]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s04_qp_1.pdf

Q16 and 31
help pls?!

 

[Hassan Ali Abid]

yes
about halogens, i thought the same thing.. but i had a question in a test, of second MCQ type.. it said that astatine is below Iodine, what r the likely properties of At? one of the sentences was that At forms diatomic molecules which dissociate more readily than Chlorine (1st sentence) i thought its wrong and so automatically marked it C but answer was wrong.. does this has to do with volatility?

astatine is more stable then cl coz of strong wanderwaals as comparing cl so may be it is having some link with the volatily ...but it depends on question that what was asked in it

 

[Hassan Ali Abid]

can anyone tell me how to determine which acid is stronger than the other using as concepts only.
for e.g write the correct order of strength of acid in increasing order for ethanoic acid chloroethanoic acid and phenol

the one which produces more H+ ions is a stronger one ....now just see that which produces more H+ ions

 

[Hassan Ali Abid]

Hassan Ali Abid
one more question.. is At (below I) a reducing agent? i read in one of the notes but according to the question mentioned above, it is not (it was pne of the wrong sentences that said "It is a powerful reducing agent" ...or is it a reducing agent but not a powerful one?

hydroden halides are Reducing agents .....and power of reducing agent increases down the group ..... HCl<HBr<HI.......
p.s the non metals (helogens cl,br,I) are not reducing agents ...they are O.A .....metals are R.A...

and lastly i didnt get what you were saying above but i tried to explain what i have understood

 

[unseen95]

For question 2,
Chlorine has 2 isotopes 35 and 37
And they are asking how many peaks are formed with Cl2+

Now, look at the formula again, it 2 of Cl...
so consider the possible arrangements
35-35
35-37 (which is same as 37-35)
37-37

So the number of peaks shall be 3, answer is B

For question 10, (according to me way)
Now you have an equation
1 -> 2 ( tht is the equation showing the mole only )
50% of the reactant dissociate.
Since mole ratio is 1:2 so for every 50% dissociation 2 x 50% is formed
thus 50% give 100% and the total thing is 100 + 50 = 150

to find Kp u need to know the formula
P product/ P reactant (P is partial pressure)

Now to find P of product u take ratio of product that is 100% and divide by total percentage that is 150%
this gives 2/3 as answer

Now for the P of reactant u take ratio of reactant that is 50% and divide by total percentage that is 150%
this gives 1/3 as answer

Now place them in formulea

(2/3) / (1/3)

BUT this is wrong, since i forgot to square the product. ( Remember the mole ratio ! )

so it should be

(2/3) ^2/ (1/3)

Do this in you calculator, and you get 4/3.

I am sure there is an easy way. But sorry that is the way I do it.

i really appreciate your help keep helping people

 

[syed1995]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s04_qp_1.pdf

Q16 and 31
help pls?!

Well mate you're in the wrong section. The paper you linked is from IGCSE and you are posting in the A Levels section.

The answer for both will be D.

16: The oxidation number of Cu is going from +2 to 0 .. meaning it's gaining electrons and is being reduced.
Since OIL RIG (Oxidation Is Loss (of electrons) while Reduction Is Gain (of electrons) and CO is a strong reducing agent.

31. Well it's common knowledge.. But just for you to understand. These gases make acid rain by...

NO2 + H20 -> HN03 + NO (Nitric Acid)
SO2 + H20 -> HSO3 (Sulfurous Acid)

You don't need to learn these equations .. just need to know that All oxides of Nitrogen (NOx) and sulfur (SO2/SO3) make acids when reacting with rain water making the rain acidic.

 

[snowbrood]

the one which produces more H+ ions is a stronger one ....now just see that which produces more H+ ions

i do know this but how cud i use this fact to determine which acid is more stronger than the other can u explain

 

[Light Yagami]

Why is the answer C:-

 

[unseen95]

Please help me with question numbers 26 and 29 in detail. http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

 

[scouserlfc]

i do know this but how cud i use this fact to determine which acid is more stronger than the other can u explain

Youll never be asked abt strength without any info,just remember mineral acids are very strong as compared to organic and use Bronsted and Lowry theory when u can and also that Arhennius theory abt the acid being strong if it fully ionizes in water to give an excess of H+ and for bases the vice versa !

Please help me with question numbers 26 and 29 in detail. http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

Tertiary alcohol is the likely compound and to do that make a optical isomer structure,first make a carbon and attach to one end OH,the other end can have methyl,now u need to find two other hydrocarbon grps for ur isomers which are ethyl and propyl ( we use these because we need the least C atoms for our organic compound yet have an optical ... ) so answer is 7 ! Remember that optical isomers are formed when u have 4 different grps on the central atom !

29. is quite simple remember the mechanisms , for alkanes it is free radical substitution,for alkenes it is electrophillic addition and for haloalkanes they undergo their reaction by nucleophillic substitution. therefore the only homologous grp left is carbonyl compounds and their reactions occur by nucleophillic addition C is the answer

 

[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

Can someone help with this, i've tried a lot but i cant get it right

 

[unseen95]

Youll never be asked abt strength without any info,just remember mineral acids are very strong as compared to organic and use Bronsted and Lowry theory when u can and also that Arhennius theory abt the acid being strong if it fully ionizes in water to give an excess of H+ and for bases the vice versa !



Tertiary alcohol is the likely compound and to do that make a optical isomer structure,first make a carbon and attach to one end OH,the other end can have methyl,now u need to find two other hydrocarbon grps for ur isomers which are ethyl and propyl ( we use these because we need the least C atoms for our organic compound yet have an optical ... ) so answer is 7 ! Remember that optical isomers are formed when u have 4 different grps on the central atom !

29. is quite simple remember the mechanisms , for alkanes it is free radical substitution,for alkenes it is electrophillic addition and for haloalkanes they undergo their reaction by nucleophillic substitution. therefore the only homologous grp left is carbonyl compounds and their reactions occur by nucleophillic addition C is the answer

thanks man, keep helping people

 

[darknessinme]

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

Can someone help with this, i've tried a lot but i cant get it right

You just have to try each option to see if it works, using the given stoichiometric equation.
Going straight to B: If you had two moles of P originally and then x mol of R were present at equilibrium, then you'd expect 2x mol of Q to be formed at equilibrium. Furthermore you'd use up 2x mol of P, so that there is 2-2x mol of P at equlibrium. If you add the total: 2-2x+2x+x=2+x