Does anyone know whether we have to know the details of the hydrogen oxygen fuel cells? Are we expected to remember the equations that take place at each electrode?

In the spec it says (j) explain that a fuel cell uses the energy from
the reaction of a fuel with oxygen to create a
voltage;

Reply 233

pcorbett94

Original post by karo16

Does anyone know whether we have to know the details of the hydrogen oxygen fuel cells? Are we expected to remember the equations that take place at each electrode?

In the spec it says (j) explain that a fuel cell uses the energy from
the reaction of a fuel with oxygen to create a
voltage;

We are not "expected" to know the equations as far as the syllabus is concerned, but we are instead meant to be able to construct them when they give us pointers. My teacher told us to just remember the oxygen reduction half equation in both acidic and alkaline conditions, and then by using the overall "combustion" equation, deduce the other half equation.

Hope that made any sort of sense.

Reply 234

S_Azizi

Do we have to know how to distinguish between square planar complexes and tetrahedral complexes?

Reply 235

mathsclown

7

First module done = mainly calculations I guess
Starting the rates module should have that and the half cell stuff done today, then finish off transition metals and the thermodynamics part by friday, then one week to do past papers!!

(edited 11 years ago)

Reply 236

silver0

1

Original post by mathsclown

First module done = mainly calculations I guess
Starting the rates module should have that and the half cell stuff done today, then finish off transition metals and the thermodynamics part by friday, then one week to do past papers!!

I'm basically doing similar revision to you, and I hope to finish this week then concentrate on past papers next week :smile:

damn this unit is hard...

Reply 237

rasklatz

For the thiosulfate/iodine and hydrogen peroxide titrations are we meant to memorise any equations?

Reply 238

chemicalX

1

Original post by Killjoy-

It's here: http://www.thestudentroom.co.uk/showthread.php?t=1918089&page=6&p=37542315&highlight=jan%202012#post37542315
MS is further down the page.

Thank Cath-ay and maddy93x.

Hi does anybody know how to do ratio buffer questions, similar to the jan 12 mock we did? those questions are so confusing, anybody know how to tackle such questions?

Reply 239

Killjoy-

8

Original post by chemicalX

Hi does anybody know how to do ratio buffer questions, similar to the jan 12 mock we did? those questions are so confusing, anybody know how to tackle such questions?

You may want to use this equation:

\mathrm{pH}=\mathrm{pK_a} + \mathrm{log\frac{[A^{-}]}{[HA]}}

It is simply a logarithmic form of the K_a equation you are used to.

Remember

\mathrm{[A^{-}]}

and

\mathrm{[HA]}

are the concentrations of conjugate base and undissociated acid at equilibrium.
So

\mathrm{log\frac{[A^{-}]}{[HA]}}

represents the log to base 10 of conjugate base: acid ratio.

You need to find

\frac{[A^{-}]}{[HA]}

at equilibrium but in order to do this you need to find the

\mathrm{pK_a}

value for the carbonic acid first.

1. The clue is to notice that you have been given the ratio at a particular pH, so this will enable you to find

\mathrm{pK_a}

and use it to answer the question.

2. Once you have found pKa you sub it into the equation with the pH of blood the patient has and solve for the ratio.

I can't really type out all the working but I'll attach a picture:

Alternatively you may use the other form of the Ka equation, but that will involve more anti-logging I think.

WP_000064.jpg368.2KB

OCR Chemistry A F325 Equilibria, Energetics and Elements Wed 13 June 2012

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