Edexcel Chemistry Unit 2 unofficial mark scheme

Cant remember many, feel free to remind me of the questions

About hydrolysis of halogenoalkanes
- Ethanol as solvent because halogenoalkane is insoluble in water
- 5 mins to make sure all the test tubes are at the same temperature for a fair test
- silver bromide, Ag+ + Br- ==> AgBr
- 2-bromobutane (secondary), 2-methyl-2-bromopropane (tertiary), 2-methyl-1-bromopropane (primary)
- Iodo>bromo>chloro because C-I bond is the longest and the weakest
- sodium hydroxide is faster because OH- is a stronger nucleophile
- PCl5: steamy white fume, dichromate: from orange to green, PCl5 is more suitable because the sodium hydroxide in the reaction mixture can neutralise the dilute sulphuric acid, so the test may fail to work with dichromate (that is my answer, and I still believe in it)

About carbonate
- add dilute HCl, pass the gas through lime water
- BaCO3(s)+2HCl(aq)==>BaCl2(aq)+H2O(l)+CO2(g)
- CO2(g)+Ca(OH)2(aq)==>CaCO3(s)+H2O(l)
- Dip nichrome wire into conc HCl, heat at the hottest part of flame until it produces no colour, then dissolve the samples in HCl, dip the wire in, heat it again
- electrons are promoted to higher energy levels when heated. when they drop to ground state they release photons of characteristic frequencies, some of which are in visible spectrum and appear as flame colours
- Mg2+ Ca2+
- Mg no colour because the photons are outside of visible spectrum
-Down the group cationic radius increases whilst the charge stays 2+. Charge density decreases so the polarising power decreases. Anion is distorted less and the C-O bonds are more stable, requiring more energy to break. Results in high thermal stability

Green chemistry
- clean fuel releases less pollutants when burnt
- greenhouse gases have polar bonds which change their dipoles and absorb IR reflected off earth, and re-emit them. Have trapping effect of heat within earth’s atmosphere
- Methane is more potent because it has four polar bonds whereas CO2 only has two

Section C
- 1.88mgdm^-3, so within the range
- not reliable because concentration may vary depending on the position from which the sample was taken
-Br2 less volatile because it’s got more electrons so stronger dispersion force, requiring more energy to break the attractions between the molecules
- As pH is increased the concentration of H+ is decreased. Therefore the forward reaction is favoured to conteract the change in concentration of H+ so equilibrium shifts to the right. Resulting in increased concentration of OBr- but decrease in concentration of HOBr
- Too high pH, corrosive, harmful to swimmers

Lel, would rep for this but prsom For the last bit of section C, I think I said it could be an irritant to swimmers skins? Reckon thats sufficient to get the mark ?

Cant remember many, feel free to remind me of the questions

About hydrolysis of halogenoalkanes
- Ethanol as solvent because halogenoalkane is insoluble in water
- 5 mins to make sure all the test tubes are at the same temperature for a fair test
- silver bromide, Ag+ + Br- ==> AgBr
- 2-bromobutane (secondary), 2-methyl-2-bromopropane (tertiary), 2-methyl-1-bromopropane (primary)
- Iodo>bromo>chloro because C-I bond is the longest and the weakest
- sodium hydroxide is faster because OH- is a stronger nucleophile
- PCl5: steamy white fume, dichromate: from orange to green, PCl5 is more suitable because the sodium hydroxide in the reaction mixture can neutralise the dilute sulphuric acid, so the test may fail to work with dichromate (that is my answer, and I still believe in it)

About carbonate
- add dilute HCl, pass the gas through lime water
- BaCO3(s)+2HCl(aq)==>BaCl2(aq)+H2O(l)+CO2(g)
- CO2(g)+Ca(OH)2(aq)==>CaCO3(s)+H2O(l)
- Dip nichrome wire into conc HCl, heat at the hottest part of flame until it produces no colour, then dissolve the samples in HCl, dip the wire in, heat it again
- electrons are promoted to higher energy levels when heated. when they drop to ground state they release photons of characteristic frequencies, some of which are in visible spectrum and appear as flame colours
- Mg2+ Ca2+
- Mg no colour because the photons are outside of visible spectrum
-Down the group cationic radius increases whilst the charge stays 2+. Charge density decreases so the polarising power decreases. Anion is distorted less and the C-O bonds are more stable, requiring more energy to break. Results in high thermal stability

Green chemistry
- clean fuel releases less pollutants when burnt
- greenhouse gases have polar bonds which change their dipoles and absorb IR reflected off earth, and re-emit them. Have trapping effect of heat within earth’s atmosphere
- Methane is more potent because it has four polar bonds whereas CO2 only has two

Section C
- 1.88mgdm^-3, so within the range
- not reliable because concentration may vary depending on the position from which the sample was taken
-Br2 less volatile because it’s got more electrons so stronger dispersion force, requiring more energy to break the attractions between the molecules
- As pH is increased the concentration of H+ is decreased. Therefore the forward reaction is favoured to conteract the change in concentration of H+ so equilibrium shifts to the right. Resulting in increased concentration of OBr- but decrease in concentration of HOBr
- Too high pH, corrosive, harmful to swimmers

If this is all right then the test was great! How many marks was the carbonate question?

yeah should be

any multiple choice answers?

Cant remember many, feel free to remind me of the questions

Multiple choice (order is totally messed up)
- BeCl2 is 180 degrees
- For ketone and aldehyde one, the wrong statement was the one which said "they have different molecular ion peaks"
- H2SO3 acting as oxidising agent in the reaction with H2S, forming 3S
- IR with ketone under reflux is C=O
- Maxwell-Boltzmann: shifts to the right and lower peak for increased temperature, no change for concentration, the activation energy line goes to the left without change in peak for catalyst
- Covalency increases NaCl to AlCl3 (charge density increases so more polarisation of anion)
- Boiling point increased in this order: branched Cl, non branched Cl, branched I, non branched I
- Buckyball is soluble because it is a simple molecule

About hydrolysis of halogenoalkanes
- Ethanol as solvent because halogenoalkane is insoluble in water
- 5 mins to make sure all the test tubes are at the same temperature for a fair test
- silver bromide, Ag+ + Br- ==> AgBr
- 2-bromobutane (secondary), 2-methyl-2-bromopropane (tertiary), 2-methyl-1-bromopropane (primary)
- SN2 mechanism
- Iodo>bromo>chloro because C-I bond is the longest and the weakest
- sodium hydroxide is faster because OH- is a stronger nucleophile
- PCl5: steamy white fume, dichromate: from orange to green, PCl5 is more suitable because the sodium hydroxide in the reaction mixture can neutralise the dilute sulphuric acid, so the test may fail to work with dichromate (that is my answer, and I still believe in it)

About carbonate
- add dilute HCl, pass the gas through lime water
- BaCO3(s)+2HCl(aq)==>BaCl2(aq)+H2O(l)+CO2(g)
- CO2(g)+Ca(OH)2(aq)==>CaCO3(s)+H2O(l)
- Dip nichrome wire into conc HCl, heat at the hottest part of flame until it produces no colour, then dissolve the samples in HCl, dip the wire in, heat it again
- electrons are promoted to higher energy levels when heated. when they drop to ground state they release photons of characteristic frequencies, some of which are in visible spectrum and appear as flame colours
- Mg2+ Ca2+
- Mg no colour because the photons are outside of visible spectrum
- Down the group cationic radius increases whilst the charge stays 2+. Charge density decreases so the polarising power decreases. Anion is distorted less and the C-O bonds are more stable, requiring more energy to break. Results in high thermal stability

Green chemistry
- clean fuel releases less pollutants when burnt
- greenhouse gases have polar bonds which change their dipoles and absorb IR reflected off earth, and re-emit them. Have trapping effect of heat within earth’s atmosphere
- Methane is more potent because it has four polar bonds whereas CO2 only has two

Section C
- 1.88mgdm^-3, so within the range
- not reliable because concentration may vary depending on the position from which the sample was taken
- Bond angel 104.5. 2 lone pairs, 2 bonding pairs, position of minimum repulsion, lone pairs repel more. Not sure about last point, maybe for saying bent/based on tetrahedral/2.5 depression etc
- Br2 less volatile because it’s got more electrons so stronger dispersion force, requiring more energy to break the attractions between the molecules
- As pH is increased the concentration of H+ is decreased. Therefore the forward reaction is favoured to conteract the change in concentration of H+ so equilibrium shifts to the right. Resulting in increased concentration of OBr- but decrease in concentration of HOBr
- Too high pH, corrosive, harmful to swimmers

"boiling point increased in this order: branched Cl, non branched Cl, branched I, non branched I"
surely branched I, non branched I, branched Cl, non branched Cl as there are stronger permanent dipoles in Cl than with I ?

Forgot most of multiple choice lol
Also can anyone tell me how to move thread to chemistry exam

FOr the multiple choice, the sulfuric acid one was that A? ANd the keton aldehyde one mass spec was D?

If this is all right then the test was great! How many marks was the carbonate question?