post your Physics and Chemistry querries

[webfactor]

Guyx.... New on XPF ..... So willing to solve your problems.......................
So start posting them.....

 

[paparazzi]

urgent help plz.!!! 06/o/n

Glycollic acid HOCH2CO2H and lactic acid CH3CH(OH)CO2H each give the reactions of an alcohol group and of a carboxylic acid group. Each compound will react with the other to give an ester.
(e) When one molecule of glycollic acid reacts with one molecule of lactic acid, it is possible to form two different esters.
Draw the structure of each of these esters.

i really dont know how 2 do this kind of qs.is there any quicker way or which chapter can i learn from the book???

 

[mariam]

chem p5 june 09 q2..! :roll:

and
june 08 q2 part (f)

plzz help me..!

 

[Fahad27]

Need help with May/June 2007 question 2(e)

 

[paparazzi]

october 08
2a)i)suggest values for the H-C-H and C=C=O bond angles in ketene?

 

[Kanwal]

H-C-H bond anfle is 120 b/c C makes double bond with next C so its trigonal
and C=C=O is linear so it shoud be 180

 

[AE-12]

Can u explain me this question
2H2O = 2H2 +O2
Above is the equation of steam dissociation
Q. At a high temperature and a total pressure of 1 atm, 20 % of steam is dissociated to Hydrogen and Oxygen. Calculate the pressure that each of the 3 gases exert at equilibrium ?
ii, Calculate the value of Kp giving its units.

Please explain. I will be very grateful

 

[beacon_of_light]

october 08
2a)i)suggest values for the H-C-H and C=C=O bond angles in ketene?

Now take C as central atom...it has three bonded atoms around it...two are hydrogens and one is CCO....so bond angle is 120*

C=C=O...bond angel is 180* shape is linear///and all linear compounds have linear shape..

Hope that helps u...

 

[beacon_of_light]

Need help with May/June 2007 question 2(e)

the question ends till part (d)...there's no part (e) to Q2...check that again...

 

[beacon_of_light]

urgent help plz.!!! 06/o/n

Glycollic acid HOCH2CO2H and lactic acid CH3CH(OH)CO2H each give the reactions of an alcohol group and of a carboxylic acid group. Each compound will react with the other to give an ester.
(e) When one molecule of glycollic acid reacts with one molecule of lactic acid, it is possible to form two different esters.
Draw the structure of each of these esters.

i really dont know how 2 do this kind of qs.is there any quicker way or which chapter can i learn from the book???

Two different isomers can be made...
1) consider OH of glycollic acid and COOH group of lactic acid....so the ester formed is... CH3CH(OH)CO2CH2CO2H

2) consider OH of lactic acid and COOH of glycolic acid...ESTER: HOCH2COOCH(CH3)CO2H

In this way you can make two different possible esters...since both compounds have OH and COOH...u need to go step by step as illustrated above...

Hope that helps u

 

[Fahad27]

Need help with May/June 2007 question 2(e)

the question ends till part (d)...there's no part (e) to Q2...check that again...

Chemistry
May June 2007
Paper5
Q. 2(e)

 

[MAVtKnmJ]

Where is the topic starter ... lol

 

[beacon_of_light]

I too thought the same....

 

[beacon_of_light]

Can u explain me this question
2H2O = 2H2 +O2
Above is the equation of steam dissociation
Q. At a high temperature and a total pressure of 1 atm, 20 % of steam is dissociated to Hydrogen and Oxygen. Calculate the pressure that each of the 3 gases exert at equilibrium ?
ii, Calculate the value of Kp giving its units.

Please explain. I will be very grateful

Here 's the method...

take 1mol as the initial moles of steam...while hydrogen and oxygen have 0 moles initially....

20% dissociation means that 0.2 moles of steam have dissociated and on equilibrium o.8 moles are left...so on equilibrium...hydrogen's moles will be 0.2 and oxygen's moles will be 0.1mol....the total moles on equilibrium are 1.1

next,

using dalton's law of partial pressures, find the partial pressure of each gas....and finally u have Kp's formula....insert the values to get ur answer...which is 0.57atm

 

[1992]

the one about esters.
when u add an alcohol and an acid to form ester. which one eliminates the OH group??? the acid or the alcohol

 

[beacon_of_light]

Acid gives hydrogen ion while alcohol gives OH ion...you can easily workout the formula now...start with the acid part and after COO add the rest of part of alcohol elimination OH on the alcohol....

 

[beacon_of_light]

Anymore queries post them....I have got a lot of time today...so i'll answer other queries related to As chemistry ONLY!

 

[1992]

i dont understand sigma and pi bonds. and how to draw them
for example: O/N 2007 Q1 b.ii) and d)

 

[ghetto-queen]

Anymore queries post them....I have got a lot of time today...so i'll answer other queries related to As chemistry ONLY!

how on earth do you have alot of time! we got like no time left and i cant solve any past paper fully and now im freaking out! looks like your prep is good, best of luck with it..
anyways my question is how do you find bond angles? cause all my sir thought us was 120 and 109, i never knew there was a whole range of angles to answer from :s

 

[1992]

it depends on the lone pairs available
just learn that tetrahedral shape has angle 109
piramidal has angle 107
linear shape has 180
trigonal planar has 120
bent shape is 104.5
no more