VCE Chemistry Question Thread

[lzxnl]

When a galvanic cell is being recharged, is it the anode reaction that is reversed? how come the cathode isn't reversed as well? What about in electrolysis? Thanks

Recharging a galvanic cell = electrolysing it
Both electrode reaction are reversed and the anode/cathode designations swap. Your old cathode becomes the new anode and vice versa. Your old positive electrode, however, is STILL positive. Do NOT get confused. Or else you'll look silly

[melbin123]

Im so screwed for chem 

[Reus]

Im so screwed for chem 

Yaaaaas.

[uni_student]

Does anyone know the answers to these two MC questions?

1. The gas in the gas bulb of an open-ended manometer has a pressure of 500 mm Hg when the atmospheric pressure is 760 mm Hg. The gas bulb is on the LHS and the open end of the manometer is on the RHS. The level of the mercury in the column is:      
a. 500 mm lower on the LHS      
b. 260 mm lower on the LHS      
c. 760 mm lower on the RHS   
d. 260 mm lower on the RHS

2. A second portion of gas, with a pressure of 400 mm Hg is added to the gas bulb in question 6. The level of the mercury after the additional of gas is:
   
a. 140 mm lower on the LHS      
b. 400 mm lower on the LHS      
c. 140 mm lower on the RHS
d. 240 mm lower on the RHS

thank you so much to whoever can help me!

[soNasty]

can someone please give me a quick BRIEF rundown of all spectroscopic techniques, whether or not theyre qualitative, quantitative and 1 sentence indicating what exactly they do? I need something simple to remember for exams

As in
IR Spec - Bonds stretch and vibrate, graph is transmittance against wavenumber.

etcetc PLEASE! im sure it will be of great help to those other than myself!

[soNasty]

what do:
correspond to in terms of units of volume?

[Valyria]

Hey AN,

Could someone walk me through question 10 please?

Also, are oxide ions always in aqueous form? My teacher told me they were usually in solid form in solid oxide fuel cells but in VCAA past papers, they are in aqueous form.

Thanks

[RKTR]

what do:
correspond to in terms of units of volume?

Cm^3 = mL
M^3 = 1000 L
mm^3= 0.001 mL

[lzxnl]

Hey AN,

Could someone walk me through question 10 please?

Also, are oxide ions always in aqueous form? My teacher told me they were usually in solid form in solid oxide fuel cells but in VCAA past papers, they are in aqueous form.

Thanks

Oxide ions are NEVER, EVER aqueous. Their base strength is ridiculous. Their conjugate acid, hydroxide, is a strong base; what does that say about a smaller and more charged oxide ion? They can never be aqueous.
In a solid oxide fuel cell, you're best off writing the entire metal oxide. For instance, 2FeO  + H2O => Fe2O3 + 2H+ + 2e-

[Rishi97]

In chemistry, is there a maximum number of marks that can be deducted if significant figures are not used? Like is a mark taken off everytime?

[keltingmeith]

In chemistry, is there a maximum number of marks that can be deducted if significant figures are not used? Like is a mark taken off everytime?

If you do not use significant figures, you'll lose a minimum of one mark. That is, you will lose one mark if in a question you don't report the correct amount of significant figures, and then the rest of the short answer questions you won't lost any more marks for it.

However, note that in last year's exam there was a whole question on the amount of significant figures you should report your answers to. If you didn't know how to use significant figures, you would've lost two marks on this exam - one for that multiple choice question, and one for your short answer questions. So, you should know significant figure rules in case something like that pops up again.

[magneto]

why do different carbon environments result in different chemical shifts?

thank you

and why is it that with increasing mass the chemical shift is smaller?

[lzxnl]

why do different carbon environments result in different chemical shifts?

thank you

and why is it that with increasing mass the chemical shift is smaller?

You don't need to know the reasons behind these for VCE.
For the first one, a different carbon environment means the carbon will be around atoms that attract electrons from it to varying extents (differing electronegativities) and these electrons reduce the actual magnetic field felt the carbon/hydrogen you're studying.
Hence, the energy required to flip the spin of the carbon/hydrogen will also change depending on its environment.

As for increasing mass and smaller chemical shift...really? It's often not due to the mass. Often, it's because a larger atom has a lower electronegativity and thus attracts less electrons => more electrons for the carbon/hydrogen => lower magnetic field felt => lower chemical shift

You don't need to know the specifics

[psyxwar]

Do we need to know where hydrogen bonding occurs for nitrogenous bases?

[nhmn0301]

Do we need to know where hydrogen bonding occurs for nitrogenous bases?

Pretty sure we do .