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Edexcel IAL Chemistry Unit 2 (WBIO2) / June 10th 2016

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Original post by mr.holmes
can anyone please explain the mechanism of Ammonia reacting with Haloalkanes?


It is a nucleophilic substitution reaction that is very similar to the reaction between halogenoalkanes and aqeous alkalis.

The ammonia molecule has a lone pair of electrons and thus acts as a nucleophile and is attracted to the C-Cl (C-halogen) bond, C has a positive dipole and Cl has a negative dipole (due to Cl having a greater electronegativity). Heterolytic fission occurs at that bond and -ve Cl is produced and a +ve carbon intermediate is produced.

NH3 now denotes the lone pair of electrons to the +ve carbon atom and R-CH2-NH2 is produced, HCl is produced as well from the H+ lost from NH3 and the Cl- produced at the heterolytic fission.
can someone pls explain this weird q in details . i dont get any of it
16.PNG31.6KB
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This is what i understood
As it is easier to displace iodite anion so 75% of the chlorine will react with NaI and 25% will react with NaBr
I did the following calculation but am not sure if it is correct
1465482988017.jpg46.1KB
Original post by Sumaiyya1999
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This is what i understood
As it is easier to displace iodite anion so 75% of the chlorine will react with NaI and 25% will react with NaBr
I did the following calculation but am not sure if it is correct


Unfortunately, it is incorrect. The answer was 0.333 of iodine and 0.167 of bromine produced. Moreover, why did you use 75% and 25%, why not 80% and 40% for example ??
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Wait i got it since it is easier to displace the iodide ion the chlorine will first react with all of the NaI so if u take the ratio of NaI to Cl2 according to the equation is 2:1 respectively so if there is 0.66 mol of NaI to react then 0.33 moles of Cl2 will react with it to form 0.33 mol of I2
And then if 0.33 mol of Cl2 has reacted so 0.5-0.33=0.17 mol is left which will react to form 0.17 mol of Br2
Reply 45
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lol.1555
Hey, i have a qs:

Which of the following would not be used to assess whether the use of a biofuel
produced from a crop of sugar cane is carbon neutral?
The amount of
A fuel used to operate farm machinery.
B pesticides and fertilisers used.
C energy released per tonne of biofuel.
D fuel used to process the crop

the answer is C, can anyone go through the choices and explain why they're wrong please? may seem obvious but our teacher didnt explain anything like that so pleaseee help
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To know if a feul is carbon neutral we need to look at all the ways the carbon is evolved or absorbed. All the other options involve carbon either being produced or absorbed. In the 1st option carbon is emitted when transporting, in the 2nd carbon is emitted when festilizers and pesticides are used and even in the 4th option carbon is given off but in the 3rd option there is no relation between the energy given out during combustion and the amount of carbon produced so the amount of energy is not used in the calc of something being carbon neutral so C is the correct option
I have a question regarding one of the questions from June 2014 R paper - Q3b basically asked effect on the colour of the equilibrium mixture (2HI (colourless) <---> H2 (colourless) + I2 (purple)) when pressure is increased.

I know that this question has been addressed in earlier posts of this thread and read them but I still don't understand - answer said equilibrium shifts to RHS and mixture turns darker purple, but isn't it 2 moles <--> 1 mole + 1 mole so the equilibrium is not affected and the colour remains the same?
how can i write a complete equation from 2 half equations?
Reply 49
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lol.1555
Original post by Sumaiyya1999
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To know if a feul is carbon neutral we need to look at all the ways the carbon is evolved or absorbed. All the other options involve carbon either being produced or absorbed. In the 1st option carbon is emitted when transporting, in the 2nd carbon is emitted when festilizers and pesticides are used and even in the 4th option carbon is given off but in the 3rd option there is no relation between the energy given out during combustion and the amount of carbon produced so the amount of energy is not used in the calc of something being carbon neutral so C is the correct option


Omg thank you so muchh <3 May you ace the exam tomorrow :biggrin:
Original post by mr.holmes
how can i write a complete equation from 2 half equations?


Make sure that both equations have the same number of electrons then put them together, cancelling out anything that are in both reactant and product sides.
Reply 51
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lol.1555
Original post by mr.holmes
how can i write a complete equation from 2 half equations?


1- the two half equations should be balanced, making sure to balance the net charge on both sides of each equation (i.e by adding the suitable number of electrons to each)

2- before combining the 2 half equations, both equations should have equal numbers of electrons so that they would cancel out when added. This could be achieved by multiplying one or both of the equations by a suitable number.

3- Now add all the reactants from both the equations on the LHS and the products on the RHS.

4- Finally, cancel out species which appear on both sides of the equation including the electrons.

hope this helps :smile:
Reply 52
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lol.1555
Any tips for revising Section C? Or what do i focus on or anything.... I'm failing it :frown:
First balance all the elements
Then balance the oxygen with H2O
And then balance the hydrogens with H+ ions
Then balance the charges
Then add the 2 equations and cancel everything that is same on each side
The addition is something like adding simultaneous equations
If u could give me an example i could work out on that and explain u
Thank you
Hope u get the grades u want
I think for section C u should know ur organic chemistry throughly
Reply 56
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lol.1555
Okay thanks =)
Original post by rubyvalkyrie
Make sure that both equations have the same number of electrons then put them together, cancelling out anything that are in both reactant and product sides.


thank you so much
but what about the balancing?
Original post by lol.1555
1- the two half equations should be balanced, making sure to balance the net charge on both sides of each equation (i.e by adding the suitable number of electrons to each)

2- before combining the 2 half equations, both equations should have equal numbers of electrons so that they would cancel out when added. This could be achieved by multiplying one or both of the equations by a suitable number.

3- Now add all the reactants from both the equations on the LHS and the products on the RHS.

4- Finally, cancel out species which appear on both sides of the equation including the electrons.

hope this helps :smile:


thanks so much :smile:
for step number 1, you mean the addition of electrons for balancing the chargers and the numbers for the elements right?
Original post by Sumaiyya1999
First balance all the elements
Then balance the oxygen with H2O
And then balance the hydrogens with H+ ions
Then balance the charges
Then add the 2 equations and cancel everything that is same on each side
The addition is something like adding simultaneous equations
If u could give me an example i could work out on that and explain u


thanks
here is an example if you can solve plz:smile:
ionoc eq.png29.1KB

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