Chemistry 3/4 2013 Thread

[thushan]

I'm having a lot of trouble figuring out the states of compounds, in reactions with alkanes, alkenes, alkanols etc. For example, in the substitution reaction of chloroethane and NaOH, the products are ethanol and NaCl, and they are both aqueous? And when forming an ester with a carboxylic acid and alcohol, both reactants are in the liquid state? :/ Is there some general rule for the states of compounds? Especially for alcohols, chloroalkanes and carb acids. Thanks in advance!

Also, do you have to include states when drawing up pathway reactions?

Pathway reactions - no states required.

Esterification occurs in the absence of water, specifically because to prevent the reaction of the ester with water producing the reactants again (the reaction is reversible) - so reactants in liquid state.

Otherwise, it doesn't really matter - chlorination of an alkane or alkene can occur in gaseous or organic phase, for instance. Put it this way - they wont ask you to put states (by doing it in a pathway format) unless the states are obvious.

[teany]

Pathway reactions - no states required.

Esterification occurs in the absence of water, specifically because to prevent the reaction of the ester with water producing the reactants again (the reaction is reversible) - so reactants in liquid state.

Otherwise, it doesn't really matter - chlorination of an alkane or alkene can occur in gaseous or organic phase, for instance. Put it this way - they wont ask you to put states (by doing it in a pathway format) unless the states are obvious.

ohh okay, thanks heaps! But if you put sulfuric acid above the arrow, can it be aqueous in that case? Just wondering

[brightsky]

ohh okay, thanks heaps! But if you put sulfuric acid above the arrow, can it be aqueous in that case? Just wondering

no it is invariably concentrated H2SO4(l).

[LOLs99]

How would u find out the iodine number

[teletubbies_95]

From what I know the iodine number is used to work out the number of double bonds in a compound and also the amount of iodine in 100g on a compound( i think , fatty acids predominantly?).
So according to various google searches, I saw an example which had said that 1g of fatty acid has 0.98 g of iodine, so 100 g of fatty acids has a 98 g of iodine. Thus , the iodine number is 98.

I dont know what i'm saying is right or not. We'll let the more experienced to decide that!

[Mr Keshy]

From what I know the iodine number is used to work out the number of double bonds in a compound and also the amount of iodine in 100g on a compound( i think , fatty acids predominantly?).
So according to various google searches, I saw an example which had said that 1g of fatty acid has 0.98 g of iodine, so 100 g of fatty acids has a 98 g of iodine. Thus , the iodine number is 98.

I dont know what i'm saying is right or not. We'll let the more experienced to decide that!

Ahh so it's for testing saturation/unsaturation?

[LOLs99]

I think it is used to measure the degree of unsaturation.
Oh  I see.

E.g the iodine numbed is defined as the number of grams of iodine that reacts with 100g of a fatty acid in an addition reaction. State the iodine number of palmitic acid . Molar mass shld be 256g/mol

[simba]

Okay... sorry for not posting the questions directly on here and just writing down the question numbers instead... but I've been super massively stuck on these questions and any help would be majorly appreciated!!

1. VCAA 2006 chemistry exam 2, section B, Q3a

2. VCAA 2006 chemistry exam 1, section A, Q9

3.VCAA 2009 chemistry exam 1, section B, Q4d

4. A student made 11.0g of aspirin, which represented a 62.0% yield.
What mass of salicylic acid must have been used assuming it was the limiting reactant?

Thanks everyone

[Alwin]

How would u find out the iodine number

It was on the 2009 VCAA exam, I'll link you the question (see pic)

[FlorianK]

It was on the 2009 VCAA exam, I'll link you the question (see pic)

(Image removed from quote.)

a) well you adding hygrogen atoms to the compound so it is a hydrogenation-reaction

b)
PV=nRT
n=PV/(RT) = 105.0*0.510/(8.31*293)=0.0220

c)using the theorem of the conservation of mass we can say that the mass of C10H22 is equivelant to the sum of the mass of the reacted hydrogen and the mass of the mycrene

m(H2)=0.0220*2=0.044

m(C10H22)=m(H2)+m(mycrene)=0.044+1=1.044

d)
Ok, so C10H22 is fully saturated and mycrene is polyunsaturated. So if we find the number of H2 atoms required to turn mycrene into C10H22 we would have the number of C=C double bonds.

The number of moles of C10H22 is equal to the number of moles of mycrene

n(C10H22)=m/M=1.044/142= 0.00735 = n(mycrene)

M(mycrene)=m(mycrene)/n(mycrene)=1/0.00735=136
In comparison M(C10H22)=10*12+22=142

The difference is 6g/mol so 6 Hydrogen atoms have been added, which means 3 H2 molecules reacted, which means there are 3 C=C double bonds in mycrene.

[Edward21]

CONFESSION.
I love VCE Chemistry, legit my favourite subject this year. I actually get excited about calculations  (oh god I am so sad..)
But seriously, love everything chem including this thread, I wonder how big this thread will get by the end of the year!! 

[icecream]

What is the difference between a polypeptide and a polyamide? D:

[lzxnl]

Polypeptides are only used in a biological sense; a peptide bond refers specifically to the amide bond between amino acids. Polypeptides are polymers of amino acids through peptide/amide bonds, and amino acids ONLY.
Polyamides are a broader family that encompasses polypeptides. However, they don't have to be amino acids. Imagine, for instance, the monomer 10-aminodecanoic acid. It certainly isn't an amino acid, but it can form a polyamide.

[icecream]

Polypeptides are only used in a biological sense; a peptide bond refers specifically to the amide bond between amino acids. Polypeptides are polymers of amino acids through peptide/amide bonds, and amino acids ONLY.
Polyamides are a broader family that encompasses polypeptides. However, they don't have to be amino acids. Imagine, for instance, the monomer 10-aminodecanoic acid. It certainly isn't an amino acid, but it can form a polyamide.

oooh okaay THANK YOU :DD

[aestheticatar]

Hey guys,

In regards to Mass Spec, what are the possible isotopes that are generally found?
E.g. 35Cl 37Cl 1H 2H

Also what is the name of the 'linkage' holding DNA backbone together?

Thanks heaps in advance.