OCR Salters Chemistry of Materials 2849

Calv

Ca should be 2+...
but iv no idea how to balance the equation...

i put
2C3H7COOH + CaCO3 ---> 2C3H7COO- Ca2+ + CO2 + H2O

how do u balance the charge?

I put (no idea if it's right or not, but it balanced out):

2C3H7COOH + CaCO3 --> Ca(C3H7COOH)2 + CO2 + H2O

Seemed like a bit of an effort for 2 marks, though.

sarzbabe

I also wasn't sure about the clinical trials i think i put something stupid like 'make sure its not toxic' which surly they would check before testing on humans. nevermind eh.

Dreading 2854 though..

Ehh, I suppose it could be toxic in humans but not in animals (hopefully rarely, though). It did seem like there was a lot of possible marking points for that question though.

Reply 81

beccy.

11

Calv

how come the zwitterion q is not neutral???

not sure if this is correct, but i said alkaline on the basis that there was an extra NH2 as part of the R group. It says in the revision guide to look out for things like that, and i think i had it so stuck in my head i went with it.
unless it was a ch2 and i misread (which is unlikely as 1)i find it unlikely there was a CH2 on the end of a chain, surely it'd be CH3 and 2)i was in such a panic i read everything about 8 times)

Reply 82

madima

beccy.

not sure if this is correct, but i said alkaline on the basis that there was an extra NH2 as part of the R group. It says in the revision guide to look out for things like that, and i think i had it so stuck in my head i went with it.
unless it was a ch2 and i misread (which is unlikely as 1)i find it unlikely there was a CH2 on the end of a chain, surely it'd be CH3 and 2)i was in such a panic i read everything about 8 times)

this is scaring me. i thought i looked through it carefully and only saw one NH2 group.

Reply 83

Calv

beccy.

not sure if this is correct, but i said alkaline on the basis that there was an extra NH2 as part of the R group. It says in the revision guide to look out for things like that, and i think i had it so stuck in my head i went with it.
unless it was a ch2 and i misread (which is unlikely as 1)i find it unlikely there was a CH2 on the end of a chain, surely it'd be CH3 and 2)i was in such a panic i read everything about 8 times)

i remembered both NH3+ n COO- ions were present in that q... thats y i thought its in a neutral condition.

well, maybe i was wrong...lol

2849 is alright to me but 2854s annoying me!!!

Reply 84

Aranyani

1

there was definitely another NH2 group.. but i kind of didnt click and put neutral, goddamnit.

Reply 85

lil_dreamer90

i was even sillier- i thought that the NH3+ group was the R group and didnt realise that it was part of the zwitterion and said that the NH3+ could donate a proton to water in solution and produce H30+ ion therefore its acidic. i didnt see the NH2 group ahh. im so silly :frown:

how many marks was that question?

Reply 86

Calv

prob 2 marks...

1 mark for choosing whether its acidic, neutral or alkaline...
1 mark for ur explanation.

Reply 87

lil_dreamer90

well thats 2 marks gone as my explantion was completley wrong! i bet the examiner will laugh really.. hopefully then s/he may be generous later on..

Reply 88

Aranyani

1

ha, i NEED the examiner to be generous if i have any chance of passing..

Reply 89

lil_dreamer90

aww keep your hopes up im sure you did better than you think. im just not thinking about all the horrible mistakes i know i made, and am thinking about 2854 now.