physics/Chem final prep (3 Viewers)

[jbrunero]

Can someone answer and explain ...

14). In a titration of a strong base with a strong acid, the following procedure was used:
1. A burette was rinsed with water and then filled with the standard acid.
2. A pipette was rinsed with some base solution.
3. A conical flask was rinsed with some base solution.
4. A pipette was used to transfer a measured volume of base solution into the conical flask.
5. Indicator was added to the base sample and it was titrated to the endpoint with the acid.

Which statement is correct?
(A) The calculated base concentration will be correct.
(B) The calculated base concentration will be too low.
(C) The calculated base concentration will be too high.
(D) No definite conclusion can be reached about the base concentration

 

[HyperComplexxx]

I assume its C
In 1, rinse with water then filled with acid dilutes it - it should be rinse with water, flling acid then acid added in
In 3, conical flask rinsed with base solution, adding the base solution from pipette will increase concentration of the base - it should be conical flask rinse water then add base
Looking at that, the acid is diluted so more acid will be used but since the concntration of base is incrase, even more acid will be used so C

 

[Omnipotence]

no. you shouldnt make any exam predictions at all. they can test you on anything, best way is to be prepared for everything

This.

 

[Swazz]

Is it safe to assume that content from last year won't be repeated again this year?

Yes, go through the 2010 paper and pay less attention to what has been tested already. They reversed English & Maths focuses entirely;

The humanities, they tended to focus on the harder questions that was done poorly, and re-worded them this year.
Just process of elimination I guess, but each paper has even focus on all topics.

 

[1981Grant]

Can someone answer and explain ...

14). In a titration of a strong base with a strong acid, the following procedure was used:
1. A burette was rinsed with water and then filled with the standard acid.
2. A pipette was rinsed with some base solution.
3. A conical flask was rinsed with some base solution.
4. A pipette was used to transfer a measured volume of base solution into the conical flask.
5. Indicator was added to the base sample and it was titrated to the endpoint with the acid.

Which statement is correct?
(A) The calculated base concentration will be correct.
(B) The calculated base concentration will be too low.
(C) The calculated base concentration will be too high.
(D) No definite conclusion can be reached about the base concentration

C.
In a proper titration for this the burette should be rinsed with acid, the fact that it is not means that the acid will be slightly diluted by the water, reducing its concentration. The conical flask should also be rinsed with distilled/deionised water rather than the base solution. As it is rinsed with the base solution there will be more base in there than the desired amount.

This means that the acid will be more dilute and there will be a greater of base which means that the base's concentration will be higher.

 

[jbrunero]

C.
In a proper titration for this the burette should be rinsed with acid, the fact that it is not means that the acid will be slightly diluted by the water, reducing its concentration. The conical flask should also be rinsed with distilled/deionised water rather than the base solution. As it is rinsed with the base solution there will be more base in there than the desired amount.

This means that the acid will be more dilute and there will be a greater of base which means that the base's concentration will be higher.

Thanks man! Great explanation as well.

 

[weirdguy99]

Is it better to know meissner effect or eddy current method thingy for the magnetic levitation ???

They are different shit but I was taught to talk about the opposing magnetic field due to the current in the superconductor. But meissner effect sounds more pro

The Meissner effect is completely separate to eddy current induction. If you place a magnet on a superconductor *while* it is being cooled, it will begin to rise into the air with NO initial change in magnetic flux (explained to me at USyd). The levitation occurs *only* due to the exclusion of magnetic fields.

 

[abc123yoyo]

For chemistry what are the conversions we need to know and how do we do them? Like converting things to ppm or ppb

 

[CecilyMare]

Ppm is mg/L and ppb is 1/1000 ppm

Did someone say final prep

Describe mercury cell, diaphragm cell and the membrane cell

 

[elvishtears]

Is it illegal for my teacher to not have done any pracs for the forensics option topic? she didn't even give us any sheets on any of the pracs

 

[jamesfirst]

The Meissner effect is completely separate to eddy current induction. If you place a magnet on a superconductor *while* it is being cooled, it will begin to rise into the air with NO initial change in magnetic flux (explained to me at USyd). The levitation occurs *only* due to the exclusion of magnetic fields.

this is why I asked...

wtf

 

[jamesfirst]

Well, you can make deductions. For example, industrial will not have a 7 mark solvay question, as last two years have.

I hope it's on the Natural resource thingy haha

 

[jamesfirst]

I assume its C
In 1, rinse with water then filled with acid dilutes it - it should be rinse with water, flling acid then acid added in
In 3, conical flask rinsed with base solution, adding the base solution from pipette will increase concentration of the base - it should be conical flask rinse water then add base
Looking at that, the acid is diluted so more acid will be used but since the concntration of base is incrase, even more acid will be used so C

I thought rinsing it with base doesn't affect the concentration ????

 

[1981Grant]

I thought rinsing it with base doesn't affect the concentration ????

it affects the volume. that's probably what he meant. So when you do c1v1=c2v2 it will be out.

 

[weirdguy99]

this is why I asked...

wtf

You asked whether you should explain levitation in terms of eddy current induction or the Meissner effect (implying both are valid explanations). Eddy current induction is completely wrong.

 

[jniranjan]

For astrophysics, do you have to know the equation for the PP chain and the CNO cycle?

 

[jamesfirst]

You asked whether you should explain levitation in terms of eddy current induction or the Meissner effect (implying both are valid explanations). Eddy current induction is completely wrong.

But past hsc papers had that has the sample answer. Even the CSSA ones

 

[khorne]

For astrophysics, do you have to know the equation for the PP chain and the CNO cycle?

THe overall equation, yes. But not the individual. Suffice to say you just need to outline it.

For the Meissner Effect, this is true. Due to electron spin and such, magnetic dipoles are induced when it's at Tc and a magnet is lying on it, which would repel the magnet, and actively exclude the field. However, in all other cases, lenz's law is applicable. Its only when no change in flux and the magnet is close does the dipole exclusion apply.

 

[weirdguy99]

But past hsc papers had that has the sample answer. Even the CSSA ones

Yeah, I know. The reason given to me by the USyd professor was that the exclusion explanation is mostly out of the scope of the HSC course, and that currents are induced, but not due to Lenz's Law.

 

[NubMuncher]

Yeah, I know. The reason given to me by the USyd professor was that the exclusion explanation is mostly out of the scope of the HSC course, and that currents are induced, but not due to Lenz's Law.

Umm I went to USyd as well and it was explained using faradays law and lenz's law.... Also, you said that if you put a magnet on the superconductor and then cooled it, it would begin to float. This is absolutely wrong, we were shown the exact opposite, with a magnet on top of a superconductor cooled and the magnet did not budge.