/0's Chem Questions

[lukeperry91]

Also, sulfuric is not gaseous in the first reaction because the forcing conditions are not present:
Boiling point of sulfuric acid: 337 °C
Boiling point of sulfur trioxide:  45°C
Boiling point of water: 100°C

I'd assume that the reaction occurs at temperatures below 337°C, and that's why the acid is condensed to an aqueous form.

EDIT: "Note that directly dissolving SO3 in water is not practical due to the highly exothermic nature of the reaction between sulfur trioxide and water. The reaction forms a corrosive aerosol that is very difficult to separate, instead of a liquid." wikipedia

I interpret that as it producing liquid/aqeous sulfuric acid until the exothermicity of the reaction brings the temperature above 337°C

[/0]

haha this went to page 16.. wow

If a question asks which chemical is most 'reactive', what is it really asking for? Whether it is a stronger oxidant or reductant? If so, then which of the two is it?

[hyperblade01]

To me, reactive suggests those metals such as Lithium, Sodium etc... where the solid form reacts violently with water - the metal is losing electrons

So it's looking for the stronger reductant?

[/0]

Yeah, that's what they did in Insight 2008, even though they didn't explicitly say it was the stronger reductant... so yeah I guess you're probably right

[/0]

Is an acid? According to the VCAA 2008 Sample exam it is, but it can't even donate protons!?

And is:
an acid-base equation?

[Collin Li]

It can become carbonic acid in the presence of water!

[/0]

Oh ok, so technically isn't an acid, it just has a high potential to become an acid?

[Collin Li]

Yep, so take the reaction:

CO2 + H2O -> H2CO3, and

H2CO3 + NaOH -> Na2CO3 + H2O

And add them together.

[/0]

Cool, thanks Collin!

[/0]

If you have to write the overall reaction for a hydrogen-oxygen fuel cell and you get this:



do you have to combine into to get full marks?

This is also just a general question for other scenarios e.g. () is it ok if you leave stuff in ionic form if you're not sure whether or not it's ok to combine them?

[Collin Li]

You can always combine them if they remain aqueous.

Bringing the oxide and protons together to form water (ionic to covalent) is a bit more iffy, but I think you're supposed to know that works out (oxide is a base, protons are acids)

[/0]

Ok thanks heaps

[Mao]

Oh ok, so technically isn't an acid, it just has a high potential to become an acid?

The definition of acid/base taught at VCE level isn't complete. There are three [mainstream] definitions of acids/bases:

Brønsted-Lowry
Acid: donates proton (e.g. HCl --> H+ + Cl-)
Base: accepts proton (e.g. NH3 + H+ <--> NH4+ )

Arrhenius
Acid: reacts with water to create H3O+ (e.g. CO2 + H2O <--> HCO3- + H3O+)
Base: reacts with water to create OH- (e.g. NH3 + H2O <--> NH4+ + OH-)

Lewis
Acid: accepts electrons (H+ + F- <--> HF) [H+ is the acid, H+ accepts electrons from F-, F- a Brønsted-Lowry base]
Base: donates electrons (F- + H+ <--> HF) [F- is the base, F- donates electrons to H+]

Acids and base often can fall under multiple (possibly all) of the three categories. In this case, carbon dioxide's property as an acidic gas can be thought of as an Arrhenius acid (reacting with water to form H3O+). This equilibrium is pushed to the right as [CO2(aq)] increases.

Not all acids have H+ to give away. Oxides of Arsenic (As_xO_y) also have acidic properties.

[/0]

Thanks so much mao! This has bugged me for a long time

[/0]

I'm just wondering, does LCP "partially offset" everything? Or is there a change that it doesn't partially offset?
thanks again