OCR Salters Chemistry F335 12th June 2013 Exam revision thread

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

But the question said 93% reflectance at red and 90% green and 0% blue! So surely it shouldn't drop.

What was the answer to the conditions and reagants question to add a methyl group??

What was the answer to the conditions and reagants question to add a methyl group??

no it wasn't reflectance, that was the colour mix of a computer screen to give a certain illusion that is was the same colour.

What did your curve look like, and what labels did you put?

I can't remember to be honest but I remember taking specific note that it was talking about screen colour and that our graph was wavelength based

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that is the correct answer without rounding errors. I got the same (174 3.s.f) because I didn't round until the very end.

you won't lose marks for not including rounding errors. all past paper questions like this (where rounding errors are possible) always note the number with numerous significant in the 'additional info' part of the mark scheme.

so long as you rounded to 2.s.f or more then you should get the marks.

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

You had to give a reason aswell, and a mark could be the difference between an A and a B, university or not, career or nothing, life and death

that is the correct answer without rounding errors. I got the same (174 3.s.f) because I didn't round until the very end.

edit:

i don't think ocr rounded their values because i got 174 using only the numbers on the paper.

you won't lose marks for not including rounding errors. all past paper questions like this (where rounding errors are possible) always note the number with numerous significant in the 'additional info' part of the mark scheme.

so long as you rounded to 2.s.f or more then you should get the marks.





slippery

I totally agree! Why is that we are wrong if we did work backwards on that seashell Q?

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.

fair do's.. well what do you think about mine; x axis was wavelength(might have put frequency or both), y axis was reflectance, I drew a sort of deformed curve that rose and then fell again, at the lamda max (peak of curve) I drew a line down to the wavelength and labelled yellow.. didn't know what they wanted me to do with the percentages tbh

What did your reflectance diagram look like?

Amino acids make proteins, which are the building blocks of life, and thus it would prove that human life could exist?

I was sorely tempted to write that it would prove aliens exist

What did people put for the question that asked suggest something about amino-acids in the comet?

Something to do with suggestion that life exists/existed because organisms create amino-acids? xD

I wrote to check for biological activities

I wrote amino acids make proteins which are essential for life to exist, but don't know if that applies to comet life too!

What was the formula for the antimony question ?


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What was the answer to the conditions and reagants question to add a methyl group??