CIE chemistry A level paper 4 variant 2

1. What was the interaction between NO3- and H2O?
2. What happens to the hydrated salt when heated gently, then more strongly?
3. What happens to the enthalpy change when HCl is changed to HNO3 and why?
4. Why does entropy increase in equilibrium II?
5. What concentration of the CH3NH2 was needed to drop the concentration of Cd2+ to a factor of a thousand?
6. Did anyone say CH3CH2COOH is more acidic than CH3COOH (or less acidic, I forgot) or did people just say they had the same acidity?
7. Equations for an alkaline buffer?

What did you answer for these?
Anyone got any other hard questions?

Reply 21

blablablaying

I wrote in hydrogen bond for 1, not sure about this..

6. CH3CH2COOH is less acidic than CH3COOH, cause alkyl group is electron-donating, causing extra negative charge on COO- end.

The rest i found them HARD. My answer probably would not earn me any point.

What is your answer for the Hess' Law? I got -534kJ/mol..

Reply 22

tuckerthetatman

1

Here's what I answered:
1. Hydrogen bonding
2. Water vapour given off, then brown NO2 gas is given off
3. Forgot what I answered
4. No idea
5. I got 0.0115 (probably wrong)
6. CH3COOH more acidic due to less number of alkyl groups
7. CH3NH2 + HCl ---> CH3NH3Cl
CH3NH3Cl + NaOH --> Ch3NH2 + NaCl + H2O

Reply 23

tuckerthetatman

1

Original post by blablablaying

I wrote in hydrogen bond for 1, not sure about this..

6. CH3CH2COOH is less acidic than CH3COOH, cause alkyl group is electron-donating, causing extra negative charge on COO- end.

The rest i found them HARD. My answer probably would not earn me any point.

What is your answer for the Hess' Law? I got -534kJ/mol..

My friend got -534 aswell, seems correct.

Reply 24

ValeriaMGD

I'm taking AS and A2 chemistry in october, self-teaching and have just finished the AS topics. You guys are freaking the s*** out of me.

Reply 25

ayyyLmaooo

Original post by TerraformingYou

1. What was the interaction between NO3- and H2O?
2. What happens to the hydrated salt when heated gently, then more strongly?
3. What happens to the enthalpy change when HCl is changed to HNO3 and why?
4. Why does entropy increase in equilibrium II?
5. What concentration of the CH3NH2 was needed to drop the concentration of Cd2+ to a factor of a thousand?
6. Did anyone say CH3CH2COOH is more acidic than CH3COOH (or less acidic, I forgot) or did people just say they had the same acidity?
7. Equations for an alkaline buffer?

What did you answer for these?
Anyone got any other hard questions?

Here's what I did :O

1. Hydrogen bonding
2. It releases the water ligand h20 so moisture is released. Then releases NO2 gas and O2, from the Mg(No3)2 remaining. Brown gas seen. and also test with the glowing splinter.
3. What de **** was that LOL. I think it has something to do w lattice energy.
4. The number of molecules of (aq) decreases in both eqI and eqII, but it decreases less in eqII. So entropy decreases less in eq II
5. K stab= [A]/ [C]^4 Divide [A] by 1000. so, is also divided by a 1000 since their stoichiometry is 1.1. [C]^4 is left as unknown and gained by using Kstab eq with Kstab value.
6. I said it was the same...I dont know why lol..something to do with both having no Cl atoms but almost same C chain length?
7. R-NH2 + H+ --> R-NH3+
R-NH3+ OH- ---> R-NH2 + H20

(edited 7 years ago)

Reply 26

ayyyLmaooo

1. Hydrogen bonding
2. It releases the water ligand h20 so moisture is released. Then releases NO2 gas and O2, from the Mg(No3)2 remaining. Brown gas seen. and also test with the glowing splinter.
3. What de **** was that LOL. I think it has something to do w lattice energy.
4. The number of molecules of (aq) decreases in both eqI and eqII, but it decreases less in eqII. So entropy decreases less in eq II
5. K stab= [A]/ [C]^4 Divide [A] by 1000. so, is also divided by a 1000 since their stoichiometry is 1.1. [C]^4 is left as unknown and gained by using Kstab eq with Kstab value.
6. I said it was the same...I dont know why lol..something to do with both having no Cl atoms but almost same C chain length?
7. R-NH2 + H+ --> R-NH3+
R-NH3+ OH- ---> R-NH2 + H20

Reply 27

jboentoro

Original post by glitterlitter

hello did anyone sit CIE chemistry paper 42 today?! how'd you guys find it, with the new format and all?

fingers crossed grade boundaries are low..

Oh my god this paper was really emotional. My entire class was looking for this thread since yesterday hahahah. It was pretty challenging, though still fairly manageable. If thresholds are average I might get an A overall but if they dip a lot like everyone hopes I should get an A*. Fingers crossed. There was a lot of Kstab, damn... and the synthesis wasn't as tough as usual... or was it just me??

Reply 28

jboentoro

Original post by ayyyLmaooo

Here's what I did :O

1. Hydrogen bonding
2. It releases the water ligand h20 so moisture is released. Then releases NO2 gas and O2, from the Mg(No3)2 remaining. Brown gas seen. and also test with the glowing splinter.
3. What de **** was that LOL. I think it has something to do w lattice energy.
4. The number of molecules of (aq) decreases in both eqI and eqII, but it decreases less in eqII. So entropy decreases less in eq II
5. K stab= [A]/ [C]^4 Divide [A] by 1000. so, is also divided by a 1000 since their stoichiometry is 1.1. [C]^4 is left as unknown and gained by using Kstab eq with Kstab value.
6. I said it was the same...I dont know why lol..something to do with both having no Cl atoms but almost same C chain length?
7. R-NH2 + H+ --> R-NH3+
R-NH3+ OH- ---> R-NH2 + H20

6. The acidity changes due to distance of Cl from the COOH group. When it is closer (as in CH3CH2CH2ClCOOH (was that it??) it can better delocalise the lone pair on O, thus stabilising the conjugate base. However compared to CH3CH2ClCH2COOH the Cl is further away thus it delocalises lone pair less and thus CH3CH2CH2ClCOOH is more acidic.

Reply 29

Demaciaaa

Original post by jboentoro

6. The acidity changes due to distance of Cl from the COOH group. When it is closer (as in CH3CH2CH2ClCOOH (was that it??) it can better delocalise the lone pair on O, thus stabilising the conjugate base. However compared to CH3CH2ClCH2COOH the Cl is further away thus it delocalises lone pair less and thus CH3CH2CH2ClCOOH is more acidic.

What is the unit of Kp in that question? I wrote atm^2

Reply 30

mingomango

Original post by TerraformingYou

1. What was the interaction between NO3- and H2O?
2. What happens to the hydrated salt when heated gently, then more strongly?
3. What happens to the enthalpy change when HCl is changed to HNO3 and why?
4. Why does entropy increase in equilibrium II?
5. What concentration of the CH3NH2 was needed to drop the concentration of Cd2+ to a factor of a thousand?
6. Did anyone say CH3CH2COOH is more acidic than CH3COOH (or less acidic, I forgot) or did people just say they had the same acidity?
7. Equations for an alkaline buffer?

What did you answer for these?
Anyone got any other hard questions?

My answer for 3 was that the N-H bond energy (410kjmol-1) > H-Cl bond energy (380 or something?), so more energy was required to separate H from N, so the reaction with HNO3 would be more endothermic. not entirely sure though, it was what i could come up with on the spot.

Reply 31

andysalad

1

Original post by mingomango

My answer for 3 was that the N-H bond energy (410kjmol-1) > H-Cl bond energy (380 or something?), so more energy was required to separate H from N, so the reaction with HNO3 would be more endothermic. not entirely sure though, it was what i could come up with on the spot.

Yep same

Reply 32

mingomango

Original post by andysalad

Yep same

do you want to battle me mate

Reply 33

jessedoell

2

Original post by Wallflower73

where were the organic synthesis quesions?
or reaction kinetics?
why did they bring Kp??? I almost cried in there haha

Kp?? do you mean Kstab?

Reply 34

jessedoell

2

Original post by mingomango

do you want to battle me mate

ladies lets not fight

Reply 35

jessedoell

2

Original post by TerraformingYou

1. What was the interaction between NO3- and H2O?
2. What happens to the hydrated salt when heated gently, then more strongly?
3. What happens to the enthalpy change when HCl is changed to HNO3 and why?
4. Why does entropy increase in equilibrium II?
5. What concentration of the CH3NH2 was needed to drop the concentration of Cd2+ to a factor of a thousand?
6. Did anyone say CH3CH2COOH is more acidic than CH3COOH (or less acidic, I forgot) or did people just say they had the same acidity?
7. Equations for an alkaline buffer?

What did you answer for these?
Anyone got any other hard questions?

This is what i put...

1. Hydrogen bonds
2. Water vapour comes off then brown gas
3. I said more exothermic.. but not sure was a guess tbh
4. I said cos gibbs energy was more negative... but also was a guess
5. I got 2.3 x 10-2... which i am also sure is wrong
6. nope ethanoic is more acidic
7. CH3NH2 + H+ --> CH3NH3+
CH3NH3+ + OH- ---> CH3NH2 + H2O

Reply 36

ayyyLmaooo

What about the fkin isomerism in the complex ions, were they cis-trans isomers?

Reply 37

ayyyLmaooo

Original post by jboentoro

6. The acidity changes due to distance of Cl from the COOH group. When it is closer (as in CH3CH2CH2ClCOOH (was that it??) it can better delocalise the lone pair on O, thus stabilising the conjugate base. However compared to CH3CH2ClCH2COOH the Cl is further away thus it delocalises lone pair less and thus CH3CH2CH2ClCOOH is more acidic.

but for the 1st 2 compounds, they both did not contain Cl atoms, i think one was ethanoic acid and the other propanoic

Reply 38

andysalad

1

Original post by ayyyLmaooo

but for the 1st 2 compounds, they both did not contain Cl atoms, i think one was ethanoic acid and the other propanoic

One of the three had no chlorine; the other two were 2) CH3CHCl-R-CO2H and 3) CH3-R-CHClCO2H. Exact position of chlorine was probably different to what I said but essentially the smaller distance of the chlorine from the oxygen weakened the strength of the O-H bond making the 3rd one more acidic.