C3 edexcel june 2016 unofficial mark scheme

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I can't remember exactly but it said when ammonia dissolves in water, what is the thing that causes the water to turn alkaline? And for the dissolved ions it was something like a test that doesn't involve soap to show the dissolved ions. I said to heat it and the crystalline solid that remains shows the solid that was dissolved. Also, I described the test for calcium ions using sodium hydroxide.

For that question i said it was the ammonium that was alkaline and that the formula was NH>4 is that correct or was it another ion in the soloution, the only other alkaline ion is -OH and that messed me up...

Reply 41

waudy

Original post by Ahadmerc

What did you guys get for the first calculation question? I think I remember getting 40 point something. For the second calculation question, the answer was 12.5.

Nope i got 2.4 i believe because it was 4/40*24 if im not mistaken. This gave you the gasious volume of 0.1M ammonium gas.

Reply 42

waudy

Original post by harry_16

I got 2.4 for the first calculation because it was 1 mol of the reactant with 1 mol of the product and I found 0.1 for the moles of the reactant so 0.1 x 24

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I too got that answer, i also got 1.25 for the second one i believe(1.25 or around there.)

Reply 43

VjM

Original post by waudy

I found the questions easy bar one, a question regarding equilibrium and the Haber process, it said that the production of ammonia gas increase if the temperature increase but if im not mistaken the production of ammonia in the forwards direction has a Equilibrium constant such that decreasing the temperature will favour the forwards reaction or am i misreading the question?

Yeah I was confused too but because it said the RATE and not the yield it makes sense as you would make ammonia quicker with an higher tempeeature. It does not necesarily mean the yield would increase too.

Reply 44

waudy

Original post by VjM

I gathered as much when i wrote about the fact its exothermic and that they have to compromise temperature over safety so i believe i may get one mark.

Reply 45

harry_16

Original post by waudy

The question stated that the rate of production increased, not the yield. The problem with a higher temperatures is that it favours the backwards endothermic reaction meaning that the yield is too low.

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Reply 46

waudy

Original post by harry_16

Yes but the question said the opposite about ammonia it said that by increasing the temperature the rate increases but i thought the rate of producing ammonia decreased as it is an exothermic reaction hence why i said that the production of ammonia favours the reactants being at lower temperatures.

Reply 47

Laila1999

Did people find exam easy or hard? :smile:

Reply 48

Ellie4888

For the second multiple choice on the first page you could have put b aswell as it had the same effect

Reply 49

astronomer99

what did people put for the multiple choice question where you had to do a calculation and the options where 0.6 1.0 10 or 0.1

Reply 50

Laila1999

Original post by astronomer99

what did people put for the multiple choice question where you had to do a calculation and the options where 0.6 1.0 10 or 0.1

I think I put 0.1

Reply 51

itsdatboy

I went through it with my teacher and I got about 45/60 which is a definite B, so happy :biggrin:

Reply 52

username2174765

guys when you had to calculate the volume of the gas, what was the equation? or what was the thing it gave you 4grams for? (i think it was 4)

Reply 53

rammustaunts

Original post by itsdatboy

I went through it with my teacher and I got about 45/60 which is a definite B, so happy :biggrin:

last year 46/60 was an A*...
This year i think it may go up to 49/60 but either way, you got a high A

Reply 54

rammustaunts

i think i got a calculation wrong due to a power of 10 error, all my working was right, so would i get 2 or 1 mark out of 3?

Reply 55

B1uescorpion

Was pretty happy with how it went- how many exams has everyone got left?

Reply 56

B1uescorpion

Original post by waudy

I put NH4+ and ammonium too but think the answer was OH- since that's what makes it alkali. Not sure though.

Reply 57

waudy

Original post by B1uescorpion

I put NH4+ and ammonium too but think the answer was OH- since that's what makes it alkali. Not sure though.

yes i totally get that i put NH4+ in the spur of the moment but when i look back i realise the dissociation of the OH- in the Ammonium Hydroxide and water would leave a net negative charge so i guess it was the hydroxy ion but i mean 1 mark for trying i guess Error carried forward if i get the formula correct xD