GCSE OCR 21st Century B7 C7 P7 - W/C - Monday 20th June 2016

Just think that you will never have to do chemistry again after tomorrow!!

idk I prefer chemistry in general to physics and bio so hoping it goes well...still not too sure about some parts though how did you find the c4-6 paper?

Haber process:
Ammonia (2NH₃) is made by reacting nitrogen (N₂) and hydrogen (3H₂) together at a pressure of 200 atmospheres, a temperature of 450°C and using an iron catalyst. The process by which this is done industrially is called the Haber process. The reaction is reversible, meaning that not all of the nitrogen and hydrogen will be converted into ammonia as some ammonia will also break down. However none of the reactants are wasted, as those that are not used are recycled and passed through again.

Le Chatelier's principle:
Le Chatelier's principle states that in dynamic equilibrium, the position of equilibrium shifts to try to cancel out any changes you make. For example: A + B ⇌ C + D. Increasing the concentration of A means more C and D are produced to counteract the change. If the reaction is exothermic in the forward direction and endothermic in the backwards direction, heating the mixture means the equilibrium moves to the left to counteract the change. If A + B ⇌ C, compressing (increasing the pressure of) the mixture means the equilibrium moves to the right to counteract the change. If there are more molecules in one side of the equilibrium than the other, the equilibrium will shift to the side with fewer molecules to counteract the imbalance.

You make everything sound so simple
You will be fine tomorrow!

Can someone please explain gas chromatography to me, I don't get it and have a funny feeling it is going to come as a 6 marker

You make everything sound so simple
You will be fine tomorrow!

Tomorrow ? My P7 OCR 21st Century exam is on Friday ?


⚔🛡⚔~Nothing happens to anyone that he is not fitted by nature to bear - Maximus Decimus Meridius~⚔🛡⚔

If someone could explain how to do this standard solution question it would be really helpful
The answer is 25 cm cubed of stock solution and make up to 20 cm cubed of water.
Thanks
edit: nevermind, understood it
Posted from TSR Mobile

I'm really confused by this, would you be able to explain it and/or post the mark scheme? What year's paper is it from?

Any predictions for C7 six markers?

It's from an old specification and the mark scheme literally says the answer I mentioned above :/
I used the formula:
final concentration / initial concentration x the volume = amount to add
therefore:
6.3/63 x 250 = 25
so add 25 cm 3 of nitric acid, to make up to 250 cm3 add more (225cm3) water to get the desired volume
essentially you make the solution 10 x more dilute
That's what I understood anyway, sorry if this is really bad explanation

Thanks! I looked at your explanation and managed to figure out a way to do it that made sense to me as to why it works, here:

That works nicely too! Good luck for tomorrow