Soccerboi's questions thread

[stephanieteddy]

Hello, just have a quick question regarding the 2011 exam, MC question 19.

The question and answer say mass spectroscopy.

I thought it was mass spectrometry?

[pi]

Oh i just inferred that because it's 50ml of it, that it's in aqueous solution. So it has to state the word "solution" to be aqueous?

Yep, or it gives a molarity in "M"

[soccerboi]

Thanks VegemitePi

My brain needs refreshment:

When asked which equations are redox, acid-base and whatever else they could ask, what do you look for?
Is this correct:
Redox - look for change in oxidation numbers, i.e increase and decrease (both must be present?)
Acid-Base- look for ... is it just the transference of H atom (can be 1 or more H atom/s ?)

[Mao]

Hello, just have a quick question regarding the 2011 exam, MC question 19.

The question and answer say mass spectroscopy.

I thought it was mass spectrometry?

they're the same thing

Thanks VegemitePi

My brain needs refreshment:

When asked which equations are redox, acid-base and whatever else they could ask, what do you look for?
Is this correct:
Redox - look for change in oxidation numbers, i.e increase and decrease (both must be present?)
Acid-Base- look for ... is it just the transference of H atom (can be 1 or more H atom/s ?)

Yes for redox, and almost always yes for acid-base. Sometimes, it could be the transfer of OH- (there are other definitions too, but let's not dwell).

Example: , this is an acid-base reaction, though there isn't a H+ transfer.

[soccerboi]

VCAA 2009 MC Q7,

H^- (aq) + H₂O (l) ---> OH^- (aq) + H₂ (g)

The oxidation number of H increases from -1 to +1 and also decrease from -1 to 0. But oxygen stays the same at -2. So in this case is oxidation and reduction both occurring with the H atom? and this is still considered redox? I always thought that 2 atoms/species must be involved in a redox, but never seen a case like this one.

[thushan]

One of the H's (the H-) increases in oxidation number from -1 to 0. Another H (one in H2O) decreases in oxidation number from +1 to 0. These two H atoms form H2.

[soccerboi]

With strong/weak acids and bases, are there ways to figure if its strong or weak by just looking at it or its reaction? Or do we have to commit them to memory?

Also can someone clarify if i've classified these correctly:
NH3 - weak base
NH4⁺- weak acid
R- COOH -weak acid
NH2 - weak base
CONH (amide) - neither acid or base?

[Mao]

Yes. Though make sure you include any hydrocarbon chains when you mention acids/bases.

R-NH2 - weak base
R-CONH2 or R-CONH-R (amide) - not acidic nor basic.

[soccerboi]

Would this reaction produce ethanol?
C2H6 + OH–

[thushan]

Would this reaction produce ethanol?
C2H6 + OH–

no

[soccerboi]

can you please explain why not?

[thushan]

can you please explain why not?

put simply, because the molecule needs a site of positive charge on carbon (so the nucleophile OH- can attack that carbon). in C2H6 that positive charge doesn't exist.

partial positive charge btw like delta +

[soccerboi]

Oh ok, and can we also say that since it's an alkane, it needs to react with cl to become a chloroalkane, then with a reactant such as NaOH before it can become an alkanol?

[Tonychet2]

can you please explain why not?

put simply, because the molecule needs a site of positive charge on carbon (so the nucleophile OH- can attack that carbon). in C2H6 that positive charge doesn't exist.

partial positive charge btw like delta +

hi thushan lol i was talking to u earlier anyway i was just wondering why is that different for HCL to react with an alkene? and to soccerboi yes id think so at vce level

[Mao]

can you please explain why not?

put simply, because the molecule needs a site of positive charge on carbon (so the nucleophile OH- can attack that carbon). in C2H6 that positive charge doesn't exist.

partial positive charge btw like delta +

hi thushan lol i was talking to u earlier anyway i was just wondering why is that different for HCL to react with an alkene? and to soccerboi yes id think so at vce level

HCl + alkene is an addition reaction, that's a completely different mechanism.