VCE Chemistry Question Thread

[thushan]

It's unlikely that VCAA expects you to figure out to predict the structure of the ion that gives rise to the base peak from just the structure of the molecule itself, without giving you the m/z value of the base peak.

[Reus]

Haha yes, I knew it wasn't a requirement to do it without a graph.

[Reus]

Le Chatelier’s Principle? Can someone summarise this in the scope of this course 
Thanks.

[lzxnl]

Think negative feedback of biology. A system at equilibrium will PARTIALLY OPPOSE any changes to this equilibrium.

I say partially oppose for a reason. Let's say you initially had 10 moles of nitrogen gas in equilibrium with 5 moles of hydrogen gas and 10 moles of ammonia. If you then dump another 5 moles of ammonia gas into this system, the nitrogen concentration will increase, prompting the system to oppose that change by reducing the nitrogen concentration with a reaction of ammonia to reform nitrogen. However, no matter how the system tries to reduce the nitrogen concentration, the nitrogen concentration at the end will always be greater than the initial concentration of 10 moles/whatever volume. See why it's partially opposing?

[Reus]

Thanks!!

[Rishi97]

A 2.16g sample of an oxide of nitrogen is broken down to release nitrogen and oxygen gases. After the oxygen gas is removed, 0.56g of nitrogen remains. The oxide is likely to be:
a) NO
b) N₄O
c) NO₂
d) N₂O₅

[soNasty]

Its d)

Why?

2N2O5----> 2N2 + 5O2

n(n2o5)= 2.16/108 = 0.02 mol

n(n2)=n(n2o5)=0.02 mol

m(n2)=0.02 x 28
m= 0.56g

[Reus]

Could someone explain the process/behaviour of particles when Iron anchors undergo corrosion in deep seas?
I know it's a low frequency of collisions between oxygen molecules and iron metal which results in corrosion, but why?
Any more detail required?

[Rishi97]

Is K_w temperature dependent???

[keltingmeith]

Yes. It's 10^-14 at 298 K, and if you work at anything else, they'll work you through it so you'll know what it should be.

[lzxnl]

Is K_w temperature dependent???

Kw is the equilibrium constant for the auto-ionisation of water, i.e. H2O (l) <=> H+(aq) + OH-(aq)
It's an equilibrium constant so it must be temperature dependent

[Jason12]

where to do you mark the + and - signs on a zwitterion when it is neutral, acidic and basic?

[Yacoubb]

where to do you mark the + and - signs on a zwitterion when it is neutral, acidic and basic?

In a zwitter ion, a + is placed at the NH3+ region, and a - is placed at the COO region.

When the amino acid is placed in an acid, it behaves as a base and thus accepts protons (becoming positively charged). A + is placed at the NH3 region. (i.e. where the proton has been gained at the amino group).

When the amino acid is placed in a base, it behaves as an acid and thus donates protons (becoming negatively charged). A - is placed at the COO region (i.e. where the proton has been lost from the carboxyl group).

[Jason12]

how to join 2 nitrogenous bases together (ie. A-T or C-G)

- both are in data book but which bonds on the base join together and does dna produce any other small molecules like water after the equation like condensation reactions?

[Reus]

how to join 2 nitrogenous bases together (ie. A-T or C-G)

- both are in data book but which bonds on the base join together and does dna produce any other small molecules like water after the equation like condensation reactions?

Hyrdogen bonding between nitrogen bases. However keep in mind that adenine and thymine (purinse) have two bonds (double H bonds) and cytosine and guanine (pyrimidines) have three in between them (triple H bonds).

Well the nucleotides to form DNA, undergo a condensation reaction meaning H₂O is produced.
4 nucleotides = 3 H₂O's.