OCR Gateway Chemistry C4C5C6 - 13/06/13

is there any way of figuring out which is exo and which is endo?

Got 69/85 on the specimen paper with a consistent 21 marks on each module. Feeling very confident of an A* now.

is there any way of figuring out which is exo and which is endo?

Did you get Qu8?? As I am looking at it and I can't seem to do it (the one with the titrations)

question 8) b) if you do get could you please explain? Thanks

They will tell you which reaction is exo/endothermic. For question 8b you just take about how universal indicator would slowly change depending on pH instead of an instant change at the end point like litmus.

Got 69/85 on the specimen paper with a consistent 21 marks on each module. Feeling very confident of an A* now.

C4 Six Marked on the additional was on the history of periodic tables...

so you only got 6 on section D?

Why is it easier for hydrogen ions to be discharged not sodium in electrolysis of naOH. So like how will we know what the products will be?

so that CERTAINLY won't come up as one of ours right?...............................

Oopw, I meant 8c haha, I got 8b :P I just can't figure out 8c

I'll try to explain it. You want the concentration of nitric acid so you know you're going to have to use the formula concentration=number of moles/volume. You can work out the number of moles of nitric acid by calculating how many moles of potassium hydroxide you have since it is a 1:1 ratio. Use number of moles= concentration x volume to work out there are 0.0025 moles of KOH hence there must be 0.0025 moles of HNO(3). Now you have the number of moles you just need the volume, this can be worked out from the titration table on the previous page. You ignore number 1 as it is not concordant with number 2 and 3. Using them you get a mean titre of 20cm^3(0.02dm^3). You plug the volume (mean titre, 0.02dm^3) and the number of moles (0.0025) into the concentration formula to get 0.125 mol/dm^3. Sorry for the large amount of writing but that's the best help I can give.

Thanks a lot! I was just getting very confused at they whole question!

L'evil Fish- some of your comments are highly advanced...are you doing A-levels??...or just very good at chemistry and wider reading

None of the above

Okay for concentration and neutralization questions.

Y cm^3 of Substance A, with concentration of W mol/dm^3 is neutralized by X cm^3 of Substance B, with an unknown concentration (lets call it Z mol/dm^3(.

Find Z:
Substance A -
Number of Moles = (Y/1000)(W)

Substance B has an equal number of moles, worked out using balanced equation.

(Y/1000)(W) = (X/1000)(Z)

$Z = \frac{\frac{wy}{1000}}{\frac{x}{1000}}$

In a general sense ^

I'd just prefer it to do it step by step as I know I'd probably make an error if I did it that way. Have you done the specimen paper?

I'd just prefer it to do it step by step as I know I'd probably make an error if I did it that way. Have you done the specimen paper?

For those who just want to pass it and not understand

And no. I've seen it though, I felt it was harder than bio. But manageable I hope

It was a very easy paper, if the real exam is like that I will be a happy man