WJEC CH1 Chemistry exam - 21/05/10

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First question on the second page... that was the Mass Spec one, wasn't it? I probably totally messed it up, but I just wrote down the m/z value for the two peaks.

The two (or three...) 4-6 mark questions didn't go too well for me. The titration one was OK, but the Rate of Reaction one... not so much. I didn't know what it was that was making the organic solvent brake down,

Reply 41

bex_1_2_1

JosephRedfern

Can you remember what the question was about? I did CH1 today, and I can't remember, to be honest! Was it the one about the Ionization Energy of Magnesium?

I put D. I did put C to begin with though..

Reply 42

JosephRedfern

bex_1_2_1

I put D. I did put C to begin with though..

I updated my reply, because I remembered what the 1st question on page two was about :P. I also put D. w00t!

Reply 43

NcJns

What was the answer to the question; "Why are there more than one series of lines in the spectrum?"

Reply 44

JosephRedfern

NcJns

What was the answer to the question; "Why are there more than one series of lines in the spectrum?"

Hmm... for that one I put something about there being several excited states, and that the spectrum representing all possible transitions...

as in, it could have gone from n=4 to n=1 or from n=3 to n=1, or n=2 to n=1 etc etc

I messed up the 6 mark question on rate of reaction big time... I went on about the solution reaching saturation which slowed down the reaction... but that doesn't include anything to do with collision theory!

Reply 45

bex_1_2_1

JosephRedfern

Um yeah. I put 19 and 20 :s-smilie:

i put 100 (one of the lines on the graph) as the next question (the m/z 1). Doubt they are right though. Mine neither... I didn't really understand what they wanted us to say.

Reply 46

bex_1_2_1

JosephRedfern

I updated my reply, because I remembered what the 1st question on page two was about :P. I also put D. w00t!

I looked it up, it was D :awesome:

Reply 47

dabeztstuff

NcJns

What was the answer to the question; "Why are there more than one series of lines in the spectrum?"

i said that from an excited state, the e- does not have to fall just to n=1 as it can fall to n=2 (balmer) and n=3 (pashen).

What did everyone get for the explosion question?

I think i got 1.48x10^9 :s-smilie:

Reply 48

JosephRedfern

planetconwy1

I went to my teacher afterwards to ask about the atom economy question, and he worked out the mass of those two molecules to be 116, and apparently it was 50% :frown:

Im really pleased about the paper other than that, and maybe the question about explosives for which i got about 4,000,000KJ or something :s-smilie:

I worked it out to be 100%.. and I'm fairly confident about that. The MR of the reactant(s) was equal to the mr of the USEFUL products, so it must be 100%!

I also got a huge value for the energy released during the explosion. We got given the Delta H for one mole, so you had to go from the 400 tonnes to moles, and then multiply the delta H for one mole by the total moles of explosive.. I think.

I think that the delta H was -444, and the MR was 80... if that was correct, then as far as I am aware you had to do:

moles = mass/mr
moles = 400000000/80
moles = 5000000

5000000*-444 = -2220000000 kJ
=> Total Energy released = -2220000000 kJ

On second thoughts, That might be the wrong value for Delta H. But I think the principle is correct.

Edit: Dabeztstuff: That number ring's a bell!

Reply 49

NcJns

What was the initial rate on the graph question?
Also;
What was the molecular mass of reactant A?

Reply 50

JosephRedfern

I think i got 72... But that might be wrong. What did you get?

edit: It was probably 74.

Reply 51

dabeztstuff

ahh i think i got 74.
but then again im not 100%

Reply 52

JosephRedfern

Ah, you're probably right. Infact, i'm fairly sure you are. I remember it being an exact number.

Reply 53

dabeztstuff

JosephRedfern

Ah, you're probably right. Infact, i'm fairly sure you are. I remember it being an exact number.

what did you get for Nh3(SO)4 mass?

i think i got 66.09 tonnes ?

this paper had such damn big numbers !

Reply 54

JosephRedfern

Yeah, thanks rings a bell! I seem to remember doing something like:

34/100andsomething * the value for tonnes they gave you

I know that pretty vauge, but I think you got it right (Y)

Reply 55

abhijitnair

dabeztstuff

10^9 i didnt get that, i got 1.48 x 10^8 :s-smilie:

edit:
i actually might have got 1.48 x10^9

Reply 56

Awakening

abhijitnair

10^9 i didnt get that, i got 1.48 x 10^8 :s-smilie:

abhijit nair of WBGS - your a flipping genius!

Reply 57

JosephRedfern

What did you put for the SiH4 questoin? I got 48g, since the mr of one was half that of the other, and 96/2 = 48g

Reply 58

NcJns

For the question "Describe and expalain the changes in rate using collision theory"

I wote firstly a description of how the rate initially increases rapidly and then stops at 0.65. I then said that when reacting partilces collide they must have the required activation energy, and the catalyst present lowers this activation energy. This means more particles collide with the required activation energy, and therefore this causes the rapid rise of the rate of reaction. The rate of reaction begins to slow down and stop at 0.65 because all of reactant A has been converted.