ocr a f325 revision thread

Although what you said was correct, you described what a fuel cell is and how the hydrogen can be stored; a hydrogen economy is the use of hydrogen as a basic fuel for everything. For example, we are in an oil economy at the moment, so we use fossil fuels to power our cars etc. In a hydrogen economy, hydrogen would be used instead of this

I hope that makes sense

Is this definition in the book? unless, if I skipped it, I use the OCR book A2 chemistry



when nitric acid and copper react what gas is given off and state colour (2)

Is this definition in the book? unless, if I skipped it, I use the OCR book A2 chemistry



when nitric acid and copper react what gas is given off and state colour (2)

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No it isn't (surprisingly), I read it in the revision guide!

When copper and nitric acid react, hydrogen is given off, and it is colourless (I think) :P

hahahhaa!! excellent

Good luck my friend

Thats why I did not know what hydrogen economy meant, thats a bit of disadvantage to me, I pay more for the proper text book and they dont state what hydrogen economy means!


good attempt but its NO2 and is orange

my turn

I'm sorry about that, I didn't mean to ask you an unfair question! I know what you mean though, the Chemistry textbooks aren't cheap.

Thank you for clearing that up for me. I thought (as an acid reacts with a metal to produce a salt and hydrogen) the equation would be Cu + 2HNO3 -> Cu(NO3)2 +H2. I was wondering why NO2 is produced instead of H2? It's just out of curiosity

Okay, what atoms does cis-platin consist of and how can it act as an anti-cancer drug?

No, its not your fault its OCR fault


Its interesting that you pointed that out.

Actually the equation is

Cu + 4HNO3 ----> Cu(NO3)2 + 2NO2 +2 H2O

NO2 is formed because the HNO3 is reduced to NO2


Cis platin consists of oxygen, carbon, pt, NH3. The cis-platin is used for chemothreapy for treating cancer as cis-platin binds to DNA and prevents the replication of cancerous cell and hence, prevents the formation of tumours.

Thank you, we should let OCR know about this so they can feel our anger? :P

Ah okay, I see what you mean, thank you for that!

That is almost all correct, but cis-platin doesn't contain oxygen or carbon - it contains chlorine instead (the formula for cis-platin is [Pt(Cl)2(NH3)2]. You're right about it binding to DNA and preventing the replication of the cancerous cell as a result, well done

OMG, I was thinking about carboplatin!! silly me hahaha

Suggest 3 uses of exponential decay (3)

Haha that's okay, don't worry

Hmm...you may have got me there, I'm not completely sure :P
One possible use I can think of is using radioactive substances in PET scanning, and using substances with a short half life to reduce exposure to radiation.
Another possible use is using radioactive substances with a specific half life to generate nuclear power - those with a shorter half life could spend less time after use as dangerous radioactive waste.
I can't think of anything else right now, I'm sorry about that :O

No it fine!

Thats correct actually,
your first point is correct , second point is removal of anabolic drug and the removal of charge from capacitor.

my turn

Ah that makes sense, thank you! I'm glad I got one right, but I'll take the other two into account too

Why can endothermic reactions occur spontaneously at room temperature?

This is because with endothermic energy is being absorbed into the chemical system from the surroundings and hence, the stability in the chemical system increases and therefore, reaction is spontaneous. TdetaS>detaH

This is because with endothermic energy is being absorbed into the chemical system from the surroundings and hence, the stability in the chemical system increases and therefore, reaction is spontaneous. TdetaS>detaH

Yes that's correct Another thing you could mention is that the entropy change would need to be positive (otherwise delta G will not be less than 0), but that is all

Yes thank you


Describe how a buffer works (5 marks)

You're welcome

A buffer is a system that minimises pH change on addition of small amount of acid or base. It consists of a weak acid and a salt of the conjugate base (this provides large amounts of conjugate base needed for the buffer system to be created), and as a result of the large amount of conjugate base, there is little H+ present. When a small amount of base is added, it reacts with the small amount of H+ (e.g. OH- ions react with H+ ions to form water). As the amount of H+ decreases, the weak acid dissociates a bit more to replace the H+, shifting the equilibrium position to the right. When a small amount of acid is added the H+ reacts with the conjugate base of the weak acid to form the weak acid. As the amount of the weak acid increases, the equilibrium position shifts to the left.

I hope that's okay, sorry if it's a bit waffly!

How can you calculate the pH of a buffer system? (There are two methods in the book, if you know both feel free to include them)

Yes very good, cant think of anything else to add


To calculate the PH , the particular method I like to use is this

[H+] = Ka x [HA]/[A-]

PH= -log[H+]
or another method is

PH = Pka + log[A-]/[HA]