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OCR Salters Chemistry F335 12th June 2013 Exam revision thread Watch

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    (Original post by ActaNonVerba)
    What was the name of the oil again anyone?
    Rapeseed oil?
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    (Original post by Mattywooda)
    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
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    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?
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    anyone know answer for the benefit for human race if more co2 dissolved in ocean?


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    (Original post by potterton48)
    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
    would i get 1 out of 2 if i put 4.07
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    (Original post by ActaNonVerba)
    What was the name of the oil again anyone?
    Lineseed oil I think
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    (Original post by jsu14)
    anyone know answer for the benefit for human race if more co2 dissolved in ocean?


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    I put less co2 in the atmosphere, less co2 acting as a greenhouse gas, reduced global warming effect?
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    (Original post by Pandora's Box)
    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.. :/
    not sure it matters where the dot goes, but yeah i think you had to label them, so im guessing the two marks were for the equations, and two for naming them
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    (Original post by Sujman)
    would i get 1 out of 2 if i put 4.07
    I am not sure, if it was 3 marks then I would say you would definitely get 1 mark for converting H+ ions into pH but I am not sure as it is 2 marks. I think you would get 1 mark for the answer and 1 for the ratio of 3/1 which you wouldn't have got if you got the answer of 4.07. Sorry, it is quite a difficult question if you haven't done the buffers coursework
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    (Original post by bexisamazing)
    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
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    what was the answer to why doesn't carbon dioxide easily dissolve in water?
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    (Original post by Sujman)
    i wrote about the acidity preventing growth of certain plants
    I never even thought of that, I wasn't too sure what they were actually looking for
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    (Original post by badatgow)
    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.
    This lol I was there thinking the same thing
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    (Original post by potterton48)
    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
    This is the part I don't get - why is there 15cm3 of salt, and not still 10? When the extra added salt neutralises half of the acid, is more salt produced?

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    (Original post by thetularula)
    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?
    I ended up with butanoic acid.
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    It was quite a nice pape, i expect the wjec chem pape to be the hardest
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    I'm still baffed out here.. every source is telling me that the molecular formula for linseed oil is c57-h98-o6 (Mr = 878) .. Number moles in 0.2 g is 0.2/878=0.0002278 moles of oil, and we were shown that 1 mole of oil reacts with 6 moles of I2, so moles of I2 = 6x0.0002278=0.001367 moles of i2, so to workout mass you times by Mr of i2, 0.001367 x 253.8=0.3469 g ..but this is the mass of iodine reacting with 0.2g, so I multiplied by 500 to get mass of i2 in 100g of linseed, 500 x 0.3469= 173.5g <<<< surely this is the true iodine number of linseed oil??.. Or maybe Ocr rounded their values so a discrete iodine number could be calculated
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    (Original post by ChemWarlock)
    It was quite a nice pape, i expect the wjec chem pape to be the hardest
    No way mate, OCR harder than WJEC
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    (Original post by thetularula)
    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?
    I think it was NC-CH2-CH2-CN then HOOC-CH2-Ch2-COOH

    (Original post by jsu14)
    anyone know answer for the benefit for human race if more co2 dissolved in ocean?

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    Less global warming as less CO2 (g)

    (Original post by Sujman)
    would i get 1 out of 2 if i put 4.07
    I would think so if you showed understanding of neutralisation (a past paper was that..)

    (Original post by hardchemlife)
    what was the answer to why doesn't carbon dioxide easily dissolve in water?
    CO2 can form 2 Hydrogen bonds, H20 can form 3. More bonds broken than formed, was my thoughts.
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    Wasnt compound D butandioic acid because there were two CN groups that were hydrolysed?
 
 
 
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