Chemistry Question HSC 2007 (1 Viewer)

[tommykins]

回复: Re: Chemistry Question HSC 2007

Condensation polymer is a polymer created by removing a H2O molecule to join two monomers, eg. Cellulose is a condensation polymer of glucose.

CH2CH2 is the 'condensed structural formula' for ethene. It's just a lazy way to make structural formulas. Like say 1-propanol. The condensed structural formula would be CH3CH2CH2OH. Although this looks like the 2nd C is joined to the first 3 H, it's not the case. That's the point of the condensed structural formula. It basically breaks up each molecule into several smaller bits.
The molecular formula of propanol could be C3H8O.
The full structural formula would be...

H H H
:mx:| | |
H-C-C-C-O-H
| | |
H H H

I hope that tells you enough about what the difference between each is.

Now, to answer you question about the bromine reaction:
They rarely ask you to draw condensed structural formula for reactions. Mostly, it'd be molecular or structural. In that case, just add up all the number of atoms in the reactants/products if they ask for a molecular formula. If not, then you must draw all the bonds in the correct order, with the atoms in the appropriate positions.

Also: Although they usually say "bromine water", which is technically HOBr, they actually mean Br2, though I guess either would be marked as correct. I just find it less troublesome to use Br2 instead. Just break up the double bond and put 2 new Br atoms on each C atom. Easy work xD

And I'd kill myself if I didn't get a band 6 in chemistry =P It's my best subject xD

you seem very informed in it, good luck mate.

 

[minijumbuk]

Re: 回复: Re: Chemistry Question HSC 2007

you seem very informed in it, good luck mate.

Thanks man =) You too.

 

[Continuum]

Re: 回复: Re: Chemistry Question HSC 2007

Hi
Thanks
Im assuming that the alpha particle is a normal He atom. We know alpha particles are radioactive so im wondering why.

Alpha particles isn't a full helium atom though - just its nuclei. Alpha particles are radioactive because of their high ionisation effect, the ability to disrupt electrons in either an atom or molecule. The thing about alpha particles though is that they often have a low penetration (can be stopped by paper), so they aren't that dangerous.

The part about the bromine test I always get mixed up though, since I never know if I should use bromine or bromine water.

One thing: with bromine water, Br₂ reacts with H₂O to form BrOH and HBr at equilibrium. Most people just use BrOH, but wouldn't the HBr also react through a hydrohalogenation reaction with an alkene? It's still removing bromine and thus the its colouration, the core of the bromine test, so how come that isn't included? Any ideas?

 

[crammy90]

im confused
so a nucleus is unstable when
a) P : N ration is too high or low for the atomic number?
(does any1 know the exact cut off?)
b) its mass number is too large ??
can some1 explain these?


and for the production of transuranic elements and radioactive isotopes
are they done the same
i.e. particle accelerator (particles speed at high speeds and some particles collide/are fired into the atoms of other-->nuclear fission (or fusion whats the diff))
OR neutron bombardment (stream of neutrons fired into reacted and collide with nucleus of atoms to make ration P : N too high for the atomic number)
is that it
ive read others could some1 elaborate these thanks youuuu

 

[minijumbuk]

For making transuranic elements, linear accelerators or cyclotrons are used. They are done by targetting U-238 with smaller atoms, like carbon, nitrogen, etc...
HOWEVER, the FIRST 3 elements after Uranium, ie. Np, Pu, Am, can be made using a nuclear reactor.

Nuclear reactors can also make other radioisotopes that are not transuranic. They work by bombarding neutrons into the atom.

Just a little thing to help you remember:
Nuclear reactors for bombarding neutrons into an element
E.g. ²³⁸₉₂U + ¹₀n --> ²³⁹₉₂U --> ²³⁹₉₃Np + B (B is a beta particle, or an electron)

Linear accelerators for bombarding smaller atoms into Uranium.
E.g. ²³⁸₉₂U + ⁹₄Be --> ²⁴⁴₉₆Cm + 3 ¹₀n

Note that I just made up these equations. I'm not 100% sure if they're correct or not, but I think that's the general way it goes.


And a) When P:N ratio is too high, that means P>N. This wouldn't be unstable. When P:N ratio too low, it means P<N. In some cases, this would be unstable. I'm not sure if there exists any "exact cut off", but I doubt they'd ask you that in the HSC. I'm screwed if they do it in mine xD
b) When mass number too large, it means that it's unable to hold itself together, so it becomes radioactive, as it decomposes.

Hope that helps.

 

[Pwnage101]

yeh, its N too high NOT P:N too high (what unstable elements u know have less neutrons than protons ?????)

 

[crammy90]

For making transuranic elements, linear accelerators or cyclotrons are used. They are done by targetting U-238 with smaller atoms, like carbon, nitrogen, etc...
HOWEVER, the FIRST 3 elements after Uranium, ie. Np, Pu, Am, can be made using a nuclear reactor.

Nuclear reactors can also make other radioisotopes that are not transuranic. They work by bombarding neutrons into the atom.

Just a little thing to help you remember:
Nuclear reactors for bombarding neutrons into an element
E.g. ²³⁸₉₂U + ¹₀n --> ²³⁹₉₂U --> ²³⁹₉₃Np + B (B is a beta particle, or an electron)

Linear accelerators for bombarding smaller atoms into Uranium.
E.g. ²³⁸₉₂U + ⁹₄Be --> ²⁴⁴₉₆Cm + 3 ¹₀n

Note that I just made up these equations. I'm not 100% sure if they're correct or not, but I think that's the general way it goes.


And a) When P:N ratio is too high, that means P>N. This wouldn't be unstable. When P:N ratio too low, it means P<n. some="" cases,="" this="" would="" be="" unstable.="" not="" sure="" there="" exists="" any="" exact="" cut="" off="" ,="" but="" doubt="" d="" ask="" you="" that="" the="" hsc.="" i="" m="" screwed="" if="" they="" do="" it="" in="" mine="" xd="">
b) When mass number too large, it means that it's unable to hold itself together, so it becomes radioactive, as it decomposes.

Hope that helps.

yeh it does nice
just to clarify
a) you couldnt accellerate a radioactive isotope that wasnt a transuranic element? youd have to neutron bombard?
b) so basically a nucleus is instable if the atom is really have and doesnt have enough protons? Is this because as the atom gets heavier its nucleus expands (more neutrons) and so brings the nucleus closer to the electrons in the rings around them and then the protons are attracted more heavily to these electrons and soemthing happens?
ahaha just made that up but sorta makes sense to me lol like the electrons could pull out neutrons from the neucleus as they are closer or somthin lol
c) if we had to answer "explain ways transuranic elements and radioactive isotopes are produced" would we write accelerators and then neutron bombardment and say how they work and then write "radioactive isopotes which are not transuranic elements are made using one of the techniques above - neutron bombardment". or do we do them separately?
thanks heaps
u are always here to answer my questions minijumbuk
and dan20 goes good too lol
</n.>

 

[minijumbuk]

a) I'm not sure if I understood your question, but I think that's right.
b) I have no idea what you just said =O
c) Neutron bombardment ONLY produces non-transuranic elements and number 93,94,95.
Accelerators are used for >95 elements.
So if you get that question, you'd say that non-transuranic radioisotopes are made using nuclear reactors, using the principle of neutron bombardment --> Beta decay etc...
For transuranic elements >95, you need accelerators, bombarding particles into the uranium 238.

 

[crammy90]

yeh, its N too high NOT P:N too high (what unstable elements u know have less neutrons than protons ?????)

Excell
"they may be manufactured in a cyclotron(particle accelerator) in which protons are introduced to the nucleus, resulting in a deficiency of neutrons(proton-rich)"
so i thought that yeh, but accelerating the hydrogen atoms in the vacuum chamber and then inserting the target substance, the h-atoms collide with the atom's nucleus to produce this proton-rich state for which radioactive properties are the result. I guess there wouldnt be more protons that neutrons, just less of a gap i.e. lower ratio of say from N 10:3 could goto 10:7 or so but i am not sure.

So if its when N is too high, does this mean the ratio of N goes from something like 10:5 to 10:1 or does high mean it does from 10:5 to 100:5. (lol now that i think of it i think there basically the same thing. If the neutrons increase its number increases and so there is more difference in the ratios)

and for this principle of N too high
does this mean the nucleus could become unstable if
a) neutrons are gained OR b) protons are lost
cause both increase the ratio yeh?


and are tranuranic >92 so uranium is only a radioisotopes, not a transuranic?
i.e. an element <92 which have been bombarded with neutrons + those ALWAYS?? with unstable nucleus i.e. >83 whos mass number is too large

 

[minijumbuk]

Sorry I don't get your post.

 

[crammy90]

Sorry I don't get your post.

basically JW about the particle accelerator where the helium is injected into the nucleus of the target element. This would mean there are more Protons yeh?
so its ratio of N is lower yeh?
so the nucleus is unstable?

cause i got confused when some1 said its only when N is too high, not too low.
so i though to myself "how could you make N too high. you could
a) increase the N OR
b) decrease the P"
but then when i read excel it said by using particle acclerators to add the H to the nuclear it becomes Proton-rich. so i thought we wouldnt this make the N low.
so then yeh according to some1 elses post even though it would be too low N it is not too high and so cannot be unstable
i hope that makes more sense
i wrote the last in a hurry

 

[Shoom]

So. Define ionisation.

 

[minijumbuk]

basically JW about the particle accelerator where the helium is injected into the nucleus of the target element. This would mean there are more Protons yeh?
so its ratio of N is lower yeh?
so the nucleus is unstable?

cause i got confused when some1 said its only when N is too high, not too low.
so i though to myself "how could you make N too high. you could
a) increase the N OR
b) decrease the P"
but then when i read excel it said by using particle acclerators to add the H to the nuclear it becomes Proton-rich. so i thought we wouldnt this make the N low.
so then yeh according to some1 elses post even though it would be too low N it is not too high and so cannot be unstable
i hope that makes more sense
i wrote the last in a hurry

Umm... I'm not sure if this will answer your question, but low N = high P:N.

So. Define ionisation.

lol =O wikipedia would've been useful for that
But it's when a stable element/molecule/whatever gets ionised, ie. by giving them a charge by either taking away or giving it more electrons.

 

[crammy90]

low N = high P:N

so they arent in relation to each other?
so if u add more neutrons you have N hightens?
and if u add protons ou have N too low?
i thought this business of too high or too low meant something like they were inrelation to eachother i.e. if N went from 20:1 to 20:10 = 2:1 which is a lower ratio than the original 20:1.

 

[minijumbuk]

Well I don't know why a N ratio would drop, but it's just simple maths.

20:1 to 2:1 would be a drop in N ratio, yes.

So yes, if you add more neutrons, then you'll just have a higher ratio. It won't decrease.

 

[Shoom]

In question 27 of the chemistry 2007 HSC exam, is that covered in the 3rd module ( not production of materials and acidic environment) and is question 17 taught in year 12?

 

[crammy90]

27 is from chem mon and man = 3rd core topic
17 is acidic environment acids and bases

 

[Shoom]

Thank God I thought it was assumed knowledge from prelim.

Thanks.

 

[minijumbuk]

20b) Sorry, I gave a wrong answer in my previous post. Lead acid cells are recharged by applying a voltage to reverse the spontaneous chemical reaction that occurs when the cell delivers current.