NSG 2020 questions I got wrong - could someone please walk me through them? (3 Viewers)

[synthesisFR]

Question 9:

Ethanol and methanoic acid will reflux to produce ethyl methanoate (an ester). You should first write out an equation for this

Determine the number of moles of both ethanol and methanoic acid. This can be done by using n = m/MM
n(ethanol) = 3.50g / 46.068 g/mol = 0.07597 mol
n(methanoic acid) = 5.75g / 60.052g/mol = 0.09575 mol
Ethanol is the limiting reagent meaning it gets used up completely.
Therefore, the n(ethyl methanoate) = 0.07597 mol since they are in a 1:1 stoichiometry ratio

Now you can calculate the mass of the product extracted
m(ethyl methanoate) = 0.07597 mol x 74.078 g/mol = 5.63g

However, the mass was found to be 24% of the expected result
So 5.63g x 0.24 = 1.35g

i hate u i wasted my time writing it down on paper
also a clean a4 sheet of paper i wasted and now i have one less of those

 

[SadCeliac]

OH WAS IT ASKING FOR ORGANIC ACID???!?!?!

OH MY GOD THAT MAKES SO MUCH SENSE :0 :0 :0

 

[bigman19191]

OH WAS IT ASKING FOR ORGANIC ACID???!?!?!

They are all acids, but yes, they were asking for organic acids.

 

[bigman19191]

i hate u i wasted my time writing it down on paper
also a clean a4 sheet of paper i wasted and now i have one less of those

my bad

 

[synthesisFR]

Question 9:

The two organic compounds are CH3CH2COOH (propanoic acid) and HOOCH (methanoic acid). They both contain a carboxyl functional group which is organic due to the presence of carbon. As such, the answer cannot the HCl nor H2SO4. HCN is not organic acid because there is no -COOH group.

im a bit confused
- some sources say Hydrogen cyanide, also known as cyanide or HCN, belongs to the class of organic compounds known as nitriles.
- we know the HCN is a weak acid
- therefore weak organic acid?!!
But some sources say that its not because
- it needs a COOH group
which one is correct

 

[nsw..wollongong]

okay WAIT that mgSO4 thing solution is in an equilirbium system right so WHEN YOU ADD MORE SOLID THEN itll dissolve bc the forward and reverse rxns you know keep going and therefore altho its a sat solution the radioactive shit will end up in both the filtrate and the residue as per the ongoing eq rxn

 

[SadCeliac]

okay WAIT that mgSO4 thing solution is in an equilirbium system right so WHEN YOU ADD MORE SOLID THEN itll dissolve bc the forward and reverse rxns you know keep going and therefore altho its a sat solution the radioactive shit will end up in both the filtrate and the residue as per the ongoing eq rxn

and for those who got the question wrong, please explain that again?

 

[synthesisFR]

I also have this question from later in the paper - no clue how to do it:
View attachment 39161

View attachment 39163
I estimated equivalence point at 8.2 ish but NO CLUE WHAT TO DO FOR C!!!

please help <3

u have the titrant volume added fromt he equivalence point.

 

[nsw..wollongong]

im a bit confused
- some sources say Hydrogen cyanide, also known as cyanide or HCN, belongs to the class of organic compounds known as nitriles.
- we know the HCN is a weak acid
- therefore weak organic acid?!!
But some sources say that its not because
- it needs a COOH group
which one is correct

whattt i was taught that it was an organic comp

 

[SadCeliac]

I also have this question from later in the paper - no clue how to do it:
View attachment 39161

View attachment 39163
I estimated equivalence point at 8.2 ish but NO CLUE WHAT TO DO FOR C!!!

please help <3

^?

 

[bigman19191]

The equivalence point is around 8 pH which lines up to a volume added of 22mL.

22mL is the amount of sodium hydroxide added against acetic acid. As always, write out a balanced equation for this reaction.

Then, you can calculate the number of moles of NaOH which is 0.022L x 0.15 mol/L = 0.0033 mol

The moles of acetic acid will also be 0.0033 mols since they react in a 1:1 ratio.

Concentration of acetic acid will therefore be 0.033 mol divided by 0.025L = 0.13 mol/L

 

[SadCeliac]

u have the titrant volume added fromt he equivalence point.

yeah... then what?

 

[bigman19191]

whattt i was taught that it was an organic comp

You were taught wrong

 

[synthesisFR]

okay WAIT that mgSO4 thing solution is in an equilirbium system right so WHEN YOU ADD MORE SOLID THEN itll dissolve bc the forward and reverse rxns you know keep going and therefore altho its a sat solution the radioactive shit will end up in both the filtrate and the residue as per the ongoing eq rxn

pre sure u cant say that..
adding a solid has no effect on eqm right

so u just instead mention common ion effect ig

 

[nsw..wollongong]

You were taught wrong

fml

 

[bigman19191]

yeah... then what?

The full explanation is in the comment

 

[SadCeliac]

The equivalence point is around 8 pH which lines up to a volume added of 22mL.

22mL is the amount of sodium hydroxide added against acetic acid. As always, write out a balanced equation for this reaction.

Then, you can calculate the number of moles of NaOH which is 0.022L x 0.15 mol/L = 0.0033 mol

The moles of acetic acid will also be 0.0033 mols since they react in a 1:1 ratio.

Concentration of acetic acid will therefore be 0.033 mol divided by 0.025L = 0.13 mol/L

you are actually a lifesaver, no idea who you are, but thank you heaps

 

[synthesisFR]

yeah... then what?

u have conc of naoh
volume of naoh
volume of acetic
find conc of acetc

 

[bigman19191]

you are actually a lifesaver, no idea who you are, but thank you heaps

I accelerated chemistry in year 10, no problem at all.

 

[SadCeliac]

thanks guys

please stick around im so close to getting to the end of the paper