VCE Chemistry Question Thread

[keltingmeith]

yep thanks IndefatigableLover 

but the thing i dont get is doesnt the valency of 4 from the lead then become the oxygen subscript in order to balance the overall charge?

So wouldnt it be   why is it then  ?

Because this is a poorly written question, designed to test you on your ability of understanding what an ionic complex is, not predicting what it looks like or what form it would take (even though it sounds like it IS testing these). In truth, this is not an effective way of determining a molecular formula of a compound, only for deciphering the simplest possible formula a compound might take on. As such, the VCE gods have deemed that you write this ionic compound in simplest form possible (i.e., PbO2 instead of Pb2O4), and if you disagree with them you will lose marks.

[lzxnl]

yep thanks IndefatigableLover 

but the thing i dont get is doesnt the valency of 4 from the lead then become the oxygen subscript in order to balance the overall charge?

So wouldnt it be   why is it then  ?

The general rule of ionic compounds is that you write the empirical formula of the compound as the molecular formula. Exceptions apply, like sodium peroxide which is Na2O2; the formula is written like this because the individual peroxide ions involve two oxygens.

I mean, the problem with ionic compounds is that they exist in a lattice. There's no simple discrete 'unit'. Even sodium chloride exists as a lattice of Na+ and Cl-; we write it as NaCl because the number of sodium and chloride ions is the same in any lattice. It's different to covalent molecules in which there are individual discrete units.

[knightrider]

Because this is a poorly written question, designed to test you on your ability of understanding what an ionic complex is, not predicting what it looks like or what form it would take (even though it sounds like it IS testing these). In truth, this is not an effective way of determining a molecular formula of a compound, only for deciphering the simplest possible formula a compound might take on. As such, the VCE gods have deemed that you write this ionic compound in simplest form possible (i.e., PbO2 instead of Pb2O4), and if you disagree with them you will lose marks.

The general rule of ionic compounds is that you write the empirical formula of the compound as the molecular formula. Exceptions apply, like sodium peroxide which is Na2O2; the formula is written like this because the individual peroxide ions involve two oxygens.

I mean, the problem with ionic compounds is that they exist in a lattice. There's no simple discrete 'unit'. Even sodium chloride exists as a lattice of Na+ and Cl-; we write it as NaCl because the number of sodium and chloride ions is the same in any lattice. It's different to covalent molecules in which there are individual discrete units.

Thanks so much Eulerfan101 and Lzxnl for clarifying 

[MNM101]

Do we need to know how to draw the reactions for fats, proteins and DNA?

[Sense]

I can't seem to put any of these together to get the polymer it shows?

[Splash-Tackle-Flail]

When naming organic compounds, what happens if the principle functional group is in a place such that we can't choose the longest carbon chain if we make the principle functional group as carbon 1. e.g. name CH2ClCH2CH(OH)CH(CH3)2

[sunshine98]

When naming organic compounds, what happens if the principle functional group is in a place such that we can't choose the longest carbon chain if we make the principle functional group as carbon 1. e.g. name CH2ClCH2CH(OH)CH(CH3)2

From what I know (pls correct me if I'm wrong) , principle functional groups such as OH and NH2 will not always fall at the end of the chain and as a result will not always take the carbon 1 ( whereas, COOH will always end of the chain and take C 1). 
So as usual you would intend to give it the lowest C number possible (which is 3 , in this case,I think).

[alchemy]

I can't seem to put any of these together to get the polymer it shows?

Is the answer (a)?
I think it works out if you try joining 'em up.

[knightrider]

How do you know whether a molecule is polar or non-polar?

[Unblemished]

I'm a bit confused in interpreting the NMR graphs presented. I look at the data book and see what it could be, but the molecule i always end up with is wrong?

[alchemy]

I'm a bit confused in interpreting the NMR graphs presented. I look at the data book and see what it could be, but the molecule i always end up with is wrong?

Are you considering the de shielding of electrons in the molecule?
When making your deductions are you going from looking at the graph to structure or structure to graph?
It helps to look at the structure first and then identify features of the graph, as an electronegative element like oxygen could be causing peaks to be shifted further downfield.

[keltingmeith]

I'm a bit confused in interpreting the NMR graphs presented. I look at the data book and see what it could be, but the molecule i always end up with is wrong?

I thoroughly discourage the use of your data-booklet for NMR. IR, definitely use it, but not for NMR. Try to use the splitting of the peak, integration, etc. to try and determine the structure of the molecule. At VCE-level, you shouldn't need to consider the chemical shift.

[Sundal]

For an ester titled: '1-butyl ethanoate' what does the '1' indicate?

Cheers !

[Sundal]

During reaction pathways would you just give the organic compounds the states that they would be found in at room temperature?

Also, how do you know when something should be considered a reactant, or placed on top of the arrow or not? (e.g. The chlorine in the chlorination process of an alkane is placed on top of the arrow, and not with the reactants. Why?)

[Sundal]

Could someone help me in understanding standard addition calibration curves.
I am having difficulty understanding these!

Thankyou.