• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Chemistry: Post your doubts here!

ahmed abdulla

ahmed abdulla

Messages
415
Reaction score
252
Points
53
strangerss said:
answer is B
amount of sulphite use = conc x vol
= 0.1 x (25/1000)
=2.5x10^-3mol
2 electrons are lost
amount of electrons lost = 2 x 2.5 x 10^-3 ==== 5 x 10^-3 mol
amount of electorns gained by metallic salt = amount of electrons lost by sulphite
= 5 x 10^-3 mol
amount of metallic salt used = 0.1 x (50/1000) ==== 5 x10^-3
amount of electrons gained PER MOLE of salt = (5 x 10^-3)/(5x10^-3) = 1 unit
hence oxidation state of metallic salt decreases by 1 unit meaning the oxidation satate becomes +2 from +3!!! this is for the question 9 , some other person posted it :D
Click to expand...

can u answer plz ...
i posted it several times but no one answered :(
 

Attachments

  • 2334.png
    2334.png
    44.2 KB · Views: 8
  • Untitled.png
    Untitled.png
    88 KB · Views: 8
Rahma Abdelrahman

Rahma Abdelrahman

Messages
2,824
Reaction score
3,730
Points
273
strangerss said:
SOSO247 OKay , in question 21 the only way to solve it is by drawing the displayed formula of the the compound. the first thing I did is I drew the cyclohexene ring you know how right? in the cyclo hexene there is 12 hydrogen atoms and 6 carbon atoms , then from the sixth carbon atom I drew a bond and counted till I reached the 11th carbon atom where I put a double bond because in the question the cis isomer is between the 11th and 12th carbon atom right? the I drew the remaing carbon atoms after the 11th one which are 9 at the last carbon atom I put the aldehyde group because it's pretty obvious it's always at the last. now the last and probably most important step is the number of double bonds between the carbon atoms , now we know that there are 12 hydrogen in the cyclohexene and two for the cis isomer and the total number of hydrogen atoms is 28(from the question) so 28-14=14 carbons (u mean Hydrogen )atoms are left to be bonded to the carbon chain , so if you give each carbon atom a hydrogen till you used 14 , you add a double bond between the carbon atoms with only three bonds and you will get six double bonds ..I will put the pic. I drew if you didn't get it ok?...question 23 it's C because we get a polychroalkene when we polymerise the monomer given right? then by reacting with water a nucleaphilic substitution reaction takes place in which the hydroxide ions which acts as a nucleaphile displaces the weaker nucleaphile the chlorine atom , it's exactly like when reacting a halognoalkane with sodium hydroxide and we get an alcohol , in A we cannot hydrate an alkane because there are no double bonds , and in B and D it's the same case we cannot oxidise an alkane , so C is correct. question 28 I really got no clue :/ . question 29 it's B because we know that a halogenoalkane plus CN will give a nitrile and when we hydrolyse a nitrile we get a carboxylic acid , when CN displaces Br in B , the final product formed will have a carbon atom attached to an ethyl group which is shown in the diagram given , notice how all the other products formed will not have an ethy group that is the C2CH3 being attached to the carbon atom that was attached to the br , did you get it ?and question 31 I don't know :/ ..hope I helped :)
Click to expand...

Thanks :D
Btw my questions r the same but with different no. due to different variant! :)
And.. check the part I marked with red above :)
 
Monysa Adhikary

Monysa Adhikary

Messages
9
Reaction score
27
Points
23
hey I want p1, p2 and p4 questions of organic chemistry only....... exam is near n its total mess.:sleep:
Can anyone help me?????

Also,I have got problems in the isomerism: how im not gonna solve it?
.................... waiting for the tips
 
S

strangerss

Messages
233
Reaction score
90
Points
38
ahmed abdulla said:
can u answer plz ...
i posted it several times but no one answered :(
Click to expand...
in the first question , where there is NH2 that mean that's where the Br was because this reaction is a nucleaphilic substitution reaction so the nucleaphile which is the NH3 will displace the weaker nucleaphile which is the Br and a hydrogen will replace the other bromine , so from the diagram given if you count from left to right the NH2 is present in the 5ht position , which means in it's place there was a Br so the only answer with a Br in the 5th carbon atom is D, that's how I figured it out , but maybe there's another way , but I hope you understood , you should start by drawing the displayed formula of the options given I suppose. In the second question an increase in pressure in the left container will push the mercury so it's level rises to the right, right?when we increase the temp. for the first reaction the equilibrium will shift to the left hand side where there is more number of moles so more pressure , in the second reaction the number of moles on both sides of the equation is the same so where ever the position of equilibrium goes the same number of moles will occupy the container , thus there is no increase in pressure and obviously in the third reaction it will make the mercury level rise to the left which is not what we want. the third question the kc of the reaction was 2:1 right?(it's given in the question)so in the second reaction they switched the reactants so the kc becomes 1:2 PLUS the number of moles is half so it should be the square root of the Kc so it would be the square root of 1/2 which is A . note: if the kc is equal to 2 this mean it's 2/1 beacuse kc is the ratio right? you might ask why we should put the square root of the answer and not divide the new kc by 2 (because the mole number in the second equation became half) and the answer for that I really don't know hehe , may be it's sort of a rule in ratios or something. hope you understood:)
 
biba

biba

Messages
172
Reaction score
147
Points
53
ahmed abdulla said:
can u help plz ;)
Click to expand...

sorry for the late reply!!!
i m confused with the organic question cuz i havnt revised organic yet :p
for equilibria:
q34: 1 is only correct because at the initial stage ,R contains twice as much gas particles as S. If this ratio is maiintained at different temperatures the pressure in r and S wil change but they wil stil be equal to each other i.e. the Hg level will not change!! in 2 and 3,N2 and the given mixture satisfies the condition i mentioned,the amount of gas in bulb remains the same!
whereas in 1 as temperature increases, the equilibrium shifts to the right since the forward reaction is endothermic. The number of gas particles increases and therefore the pressure in R will be higher than that in S.

q9: answer is A bcuz:
for reaction 1: Kc =[X2Y]^2 / [X2]^2 x [Y2] = 2 mol/dm^3
for reaction 2 : Kc = [X2][Y2]^0.5 /[X2Y] ,this becomes,
1/{[X2Y]^2 / [X2]^2 x [Y2]}^0.5 = 1/(2)^1/2
 
h4rriet

h4rriet

Messages
325
Reaction score
215
Points
53
unseen95 said:
please please please help me with question number 11 of http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf with reason.
Click to expand...

You have to make an ICE chart, i.e. initial concentration, change in concentration, and final concentration. The initial concentration of the acid and alcohol is 1 and 1. The change in concentration of the acid and alcohol is -x and -x, and the change in concentration of the ester and the water +x and +x. So the equilibrium concentration of the acid and alcohol is 1-x and 1-x, and the equilibrium concentration of the ester and water is x and x. Now you can find the Kc.
 
h4rriet

h4rriet

Messages
325
Reaction score
215
Points
53
ahmed abdulla said:
can u answer plz ...
i posted it several times but no one answered :(
Click to expand...

34. Use Le Chatelier's principle. An increase in temperatue will favour the endothermic side of the reaction. This side produces twice the number of moles. Equation 2 has the same number of moles on each side, so the temperature won't affect the number of moles produced, because the mole ratio will still be 1:1.
9. The reaction is reversed, so the Kc is the reciprocal of the forward reaction's Kc. All the moles are divided by 2, so the square root of the Kc is taken.
 
R

rawaaaan

Messages
20
Reaction score
19
Points
13
this one please
How does concentrated sulfuric acid behave when it reacts with sodium chloride?
A as an acid only
B as an acid and oxidising agent
C as an oxidising agent only
D as a reducing agent only
 
You must log in or register to reply here.
Top