OCR Salters Chemistry F335 12th June 2013 Exam revision thread

i got that too

nope it was just number of moles added (an excess). Some of it was unused (obviously) so here is the titration to calculate how much was unused.

I don't want to but a downer on your happiness however for that question the answer is pH 4.25. I don't want to sound arrogant but I did my coursework on buffers and got 44/45 marks and used this equation all the time. Basically initially the concentration is 1:1 salt to acid ratio so I imagine there was 10 cm3 of each if Half of the acid is gone then you have 5cm3 of acid. And importantly as it is a buffer there will be 15 cm3 of salt. This basically means that is 15/5 (x3) times the concentration of H+ or (ka value) getting a answer of 4.25

What was the name of the oil again anyone?

Indeed you're correct. I misremembered a question from a previous paper where you neutralised a third of the acid.

I think a lot of people got the wrong answer of 4.07 because of there failure to think where the acid goes when it reacts with sodium hydroxide

What was the name of the oil again anyone?

anyone know answer for the benefit for human race if more co2 dissolved in ocean?


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Yeah I got that equation, but... a) does it matter which side the dot goes? I can't remember where I put it.. And b) did you have to label them initiation and termination because if so I didn't read the question.. :/

would i get 1 out of 2 if i put 4.07

I put less co2 in the atmosphere, less co2 acting as a greenhouse gas, reduced global warming effect?

i wrote about the acidity preventing growth of certain plants

I found the paper overall pretty tough, but i'm confident i've done pretty well because I managed to finish quite fast and had plenty of time (like 40 mins) thankfully to check over everything a couple of times. While I was checking the paper I felt a lot better about my chances, because in hindsight most of the questions were relatively straightforwards. While doing the questions for the first time I felt like I was struggling a lot, but that's probably due to seeing unusual thinks like isoprenes etc.

The interesting question IMO was the one about the calcium carbonate shells. My reasoning was that, increasing acidity increases [H+], so second equation equilibrium concentration shifts to the right. This increases concentration of [HCO3-]. I figured this would increase the concentration of [CO3 2-] in the first equation, so equilibrium would shift to the left to oppose the change. As a result, calcium carbonate concentration would increase and the shell thickness would increase. However, writing that down made me feel like a mug the entire time because i'm pretty sure if you pour acid on calcium carbonate it would just dissolve...but I couldn't see the chemistry to disagree with me. Oh well, only 2 marks if i'm wrong anyways.

I don't want to but a downer on your happiness however for that question the answer is pH 4.25. I don't want to sound arrogant but I did my coursework on buffers and got 44/45 marks and used this equation all the time. Basically initially the concentration is 1:1 salt to acid ratio so I imagine there was 10 cm3 of each if Half of the acid is gone then you have 5cm3 of acid. And importantly as it is a buffer there will be 15 cm3 of salt. This basically means that is 15/5 (x3) times the concentration of H+ or (ka value) getting a answer of 4.25

I got a bit confused (probably a silly mind blank) on the question where they wanted to add the alkene to (CN)2 to make compound C. Then we had to hydrolyse compound C to make compound D, what would that molecule have been?