Chemistry Predictions/Thoughts (3 Viewers)

[Cathode_RT]

seems like a lot of us finished today on chem lol,
feels like nobody here does physics???

 

[blob063540]

I also just solved for mL o

Yeah I got something to the -11 but it looked really small in comparison to the other given values so don't know if i did it right

yuh yuh like 7.8 or smthn was the number and the magnitude was really small

 

[carrotsss]

yeah same I got 81.7 but was very skeptical because it seemed way too high

ill be like the 5th person to say this but yes i got 81.7 L also

 

[carrotsss]

Yay thanks.
Also carrots I'm gonna miss seeing u you're like everywhere Was chem your last exam?

I've still got physics to go

 

[jayk_217]

any solutions anywhere?

 

[Goldattacker40000]

Also for the question where they found the nh4 in the fertiliser i had no clue what to do. i had 1.55g or smth. I didnt know what to do at the step when they boiled the ammonia with NaOH

I think I got a mass of ammonium that was in between 0.1 and 1 but i dont remember the exact mass.

 

[Engineer_192931]

i got like 7.3 X10^-9 it was 7. smth

I think I got that but like 10^-11 maybe

 

[Luukas.2]

PV = nRT is the way to go for Q27 (CO₂ production from fermentation) because the gas volumes on the data sheet only apply to temperatures at 273 K and 298 K. Alternatively, if you used one of those (since the pressure matched) you would then need to adjust the volume using a Charles' Law calculation.

Question 21 is badly written as there is (technically) no correct answer. Butanone and butanal are NOT functional group isomers as they have the same functional group - carbonyl. They are different classes of compounds (a ketone and an aldehyde), but that is not the same thing as classifying them as having different functional groups. In the same way, 1-butanol, 2-butanol, and 2-methyl-2-propanol all have the same functional group (a hydroxyl) but have some differences in chemistry due to the different positioning of the functional group. In this case, though, we call all of them alcohols and consider them part of the same class.

I doubt it will cause a problem - what they wanted was obvious - but it is technically wrong.

 

[carrotsss]

PV = nRT is the way to go for Q27 (CO₂ production from fermentation) because the gas volumes on the data sheet only apply to temperatures at 273 K and 298 K. Alternatively, if you used one of those (since the pressure matched) you would then need to adjust the volume using a Charles' Law calculation.

Question 21 is badly written as there is (technically) no correct answer. Butanone and butanal are NOT functional group isomers as they have the same functional group - carbonyl. They are different classes of compounds (a ketone and an aldehyde), but that is not the same thing as classifying them as having different functional groups. In the same way, 1-butanol, 2-butanol, and 2-methyl-2-propanol all have the same functional group (a hydroxyl) but have some differences in chemistry due to the different positioning of the functional group. In this case, though, we call all of them alcohols and consider them part of the same class.

I doubt it will cause a problem - what they wanted was obvious - but it is technically wrong.

I’ve noticed ketones and aldehydes being treated as functional group isomers in trial papers asw so im not really sure, it’s definitely odd since they’re both carbonyl but maybe they’re treated as functional group isomers in the syllabus or something?

 

[Luukas.2]

I’ve noticed ketones and aldehydes being treated as functional group isomers in trial papers asw so im not really sure, it’s definitely odd since they’re both carbonyl but maybe they’re treated as functional group isomers in the syllabus or something?

Well, the syllabus and the Department of Education / NESA / etc do things their own way... and trials often have questionable content... but functional groups and compound classes are not the same thing.

And the HSC has a track record of being, shall we say, less than 100% on the accuracy front. The cadaverine ¹H NMR spectrum from a couple of years ago, for example... the mass spectrum in question 28 (compound R) in this year's paper is a touch misleading in my opinion, too.

 

[Luukas.2]

And there was Q31, which refers to a species that I'm doubtful exists.

Copper(II) ions do react with lactate anions to make a compound known as copper(II) lactate, that can be thought of as a salt or as a coordination complex: [Cu(C₃H₅O₃)₂] - that is, [Cu(CH₃CHOHCO₂)₂].

This year's HSC exam, however, claims a cationic complex (with the lactic acid in its protonated form) as [Cu(C₃H₅O₃)₂]²⁺, or as [Cu(CH₃CHOHCOOH)₂]²⁺.

Carboxylic acids form complexes and salts as anions, not in their protonated forms. The species of the composition given seems highly improbable, made more questionable by the disregard for the acidity of the uncomplexed lactic acid (with its pK_a of 3.86).

 

[Engineer_192931]

For compound R how did you know where to put the two chlorines? And what was the answer

 

[SadCeliac]

For compound R how did you know where to put the two chlorines? And what was the answer

An alkene Q will go to dichloroalkane R

 

[Luukas.2]

For compound R how did you know where to put the two chlorines? And what was the answer

The addition of chlorine to an alkene produces a dichloroalkane.

The fact that the mass spectrum appears to show only one is misleading. The product should be 1,2-dichloropropane.

The mass spectrum of the compound can be seen at this link: https://webbook.nist.gov/cgi/cbook.cgi?ID=C78875&Mask=200#Mass-Spec

You can see that it matches the spectrum provided in the exam, but with the lowest intensity peaks missing.

Taking the ³⁵Cl : ³⁷Cl ratio as 3 : 1 yields the parent (molecular) ion, [C₃H₆Cl₂]^{+ .} at m/z = 112, 114, and 116 in a 9 : 6 : 1 ratio.

 

[Engineer_192931]

The addition of chlorine to an alkene produces a dichloroalkane.

The fact that the mass spectrum appears to show only one is misleading. The product should be 1,2-dichloropropane.

The mass spectrum of the compound can be seen at this link: https://webbook.nist.gov/cgi/cbook.cgi?ID=C78875&Mask=200#Mass-Spec

I mean like how do we know it's not 1,1 or 2,2 or 1,3 ?

 

[Engineer_192931]

Wait dw I realise now

 

[Engineer_192931]

Does anyone know what were questions 33 and 35?

 

[ghreysantomy]

Solutions ?
Surely multiple choice at least

 

[=)(=]

The addition of chlorine to an alkene produces a dichloroalkane.

The fact that the mass spectrum appears to show only one is misleading. The product should be 1,2-dichloropropane.

The mass spectrum of the compound can be seen at this link: https://webbook.nist.gov/cgi/cbook.cgi?ID=C78875&Mask=200#Mass-Spec

You can see that it matches the spectrum provided in the exam, but with the lowest intensity peaks missing.

Taking the ³⁵Cl : ³⁷Cl ratio as 3 : 1 yields the parent (molecular) ion, [C₃H₆Cl₂]^{+ .} at m/z = 112, 114, and 116 in a 9 : 6 : 1 ratio.

doesnt 1,2-dichloroprop-1-ene fit cause you could assume Q might have a double bond and since doesnt specify excess cl2 it could only have 1 double bond being saturated also 1,2-dichloroprop-1-ene has 32 percent carbon by mass and has molecular ion peak at 114 it also has a fragment at 15 and 62?

 

[Jane Mao]

Solutions ?
Surely multiple choice at least

Rather than wait for some genius person who got everything right, how bout we just compile everyone’s answers.
Here’s what I had for everything
1. D
2. C
3. B
4. D
5. D
6. C
7. A
8. B
9. C
10. A
11. C
12. B
13. A
14. D
15. B
16. B
17. A
the full paper isn’t uploaded yet so I can’t check this but I think I got all A’s for 18, 19, and 20 (I rushed multiple choice so this could be wrong)
Now if anything looks wrong just tell me and I’ll edit this