uer23
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Need help with this question from OCR Biology F212 June 2009 paper (New spec)

Describe how the concentration of a reducing sugar can be measured using a colorimeter ?

It is a 6 mark question.

Would this answer be sufficient to gain full 6 marks. People who sat/done this paper, what did you write ?

- Boil glucose solution with Benedict's solution until there is no further colour change.
- Cool and filter solution.
- Take filtrate and test using a colorimeter.
- Low reading for absorbance means higher conc. of reducing sugar.
- High reading for absorbance means lower conc. of reducing sugar.

Thanks.
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logic123
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talk about calibration of the colorimeter with distilled water this helps give you a set point.
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uer23
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would this be correct...

high reading for absorbance = more light transmitted = low conc. of reducing sugar.

low reading for absorbance = less light transmitted = high conc. of reducing sugar.
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logic123
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yh
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najeezy
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I sat this paper, but i wasnt happy with the result so i ordered it back and ordered a remark.

Anyways...

heres what i wrote for this question, i was 1 short off full marks for this question.

:

The reducing sugar is first verified that it is a reducing sugar, it is placed in a beaker where benedicts solution is added and it is heated to 80(degrees/celsius) in a water bath. If a reducing sugar is present the solution will change colour from blue to orange-red, this solution is then placed in a curvette/ between a colorimeter and a photoelectric cell, the colorimeter shines a beam of light and the cell picks up the percentage transmission, this is then measure on a calibration cruve with a set of known concentrations, the value can then be read off the curve for its percentage transmission.

Exactly what i wrote, cant beleive that didnt score 6 tbh, but gl with it anyway.
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uer23
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(Original post by najeezy)
I sat this paper, but i wasnt happy with the result so i ordered it back and ordered a remark.

Anyways...

heres what i wrote for this question, i was 1 short off full marks for this question.

:

The reducing sugar is first verified that it is a reducing sugar, it is placed in a beaker where benedicts solution is added and it is heated to 80(degrees/celsius) in a water bath. If a reducing sugar is present the solution will change colour from blue to orange-red, this solution is then placed in a curvette/ between a colorimeter and a photoelectric cell, the colorimeter shines a beam of light and the cell picks up the percentage transmission, this is then measure on a calibration cruve with a set of known concentrations, the value can then be read off the curve for its percentage transmission.

Exactly what i wrote, cant beleive that didnt score 6 tbh, but gl with it anyway.
Thanks.

I'm actually retaking this unit, I done it june too. I was going to get my paper but its too late now, my college has a deadline for all this stuff. What mark did you get for this paper ?

Didn't it say on the paper what was needed for the full mark ?

Maybe you need to explain what the reading shows for that final mark ? For e.g. low reading = high reducing sugar conc.
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najeezy
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i got a crappy 102/150, to get an A you needed 66/100 raw marks, full marks would of been easy if i just was a bit more specific.
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aimz08
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(Original post by najeezy)
I sat this paper, but i wasnt happy with the result so i ordered it back and ordered a remark.

Anyways...

heres what i wrote for this question, i was 1 short off full marks for this question.

:

The reducing sugar is first verified that it is a reducing sugar, it is placed in a beaker where benedicts solution is added and it is heated to 80(degrees/celsius) in a water bath. If a reducing sugar is present the solution will change colour from blue to orange-red, this solution is then placed in a curvette/ between a colorimeter and a photoelectric cell, the colorimeter shines a beam of light and the cell picks up the percentage transmission, this is then measure on a calibration cruve with a set of known concentrations, the value can then be read off the curve for its percentage transmission.

Exactly what i wrote, cant beleive that didnt score 6 tbh, but gl with it anyway.
Thats quite useful - can I just ask what a photoelectric cell is? :o:
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najeezy
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(Original post by aimz08)
Thats quite useful - can I just ask what a photoelectric cell is? :o:
the photoelectric cell is just a cell which picks up how much light has gotten through to it % transmission.
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aimz08
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(Original post by najeezy)
the photoelectric cell is just a cell which picks up how much light has gotten through to it % transmission.
Thanks which past papers are for this module? (I know its a new syllabus I mean from the old one...)
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najeezy
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(Original post by aimz08)
Thanks which past papers are for this module? (I know its a new syllabus I mean from the old one...)
there are many from the old syllabus, the ocr website has them all.
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India27
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hey does anyone have the f212 paper from june 09?
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nima74
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i have it with me
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jords998
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For a practical endorsement (new thing in A-Level this year) we had to preform an experiment similar, we were given a unknown sample and had to determine the concentration, but we had to create our own calibration curve by testing and diluting a 1% concentration to 0.50% 0.25% 0.13% and 0.06% to create a base.
First we boiled the the glucose sample with the Benedict's solution in a water bath. We then had to centrifuge the samples to allow the precipitate to settle. Once it had settled we transferred the liquid onto into a curvette. Using a red lens we read the transmission percentage and plotted a calibration curve and read an estimate of the unknown concentration.

I can not think as to why you didn't get full marks but hopefully comparing the question to my experiment may help you figure out why. The only thing I can think about is taking negative results for non-reducing sugars and using HCL to break the bonds and turn it into a reducing sugar as there is no test for non-reducing sugars but I doubt that would be worth a mark on that question.
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sw109357
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(Original post by jords998)
For a practical endorsement (new thing in A-Level this year) we had to preform an experiment similar, we were given a unknown sample and had to determine the concentration, but we had to create our own calibration curve by testing and diluting a 1% concentration to 0.50% 0.25% 0.13% and 0.06% to create a base.
First we boiled the the glucose sample with the Benedict's solution in a water bath. We then had to centrifuge the samples to allow the precipitate to settle. Once it had settled we transferred the liquid onto into a curvette. Using a red lens we read the transmission percentage and plotted a calibration curve and read an estimate of the unknown concentration.

I can not think as to why you didn't get full marks but hopefully comparing the question to my experiment may help you figure out why. The only thing I can think about is taking negative results for non-reducing sugars and using HCL to break the bonds and turn it into a reducing sugar as there is no test for non-reducing sugars but I doubt that would be worth a mark on that question.
Hi jords998... can you explain in a bit more detail how you got and plotted the calibration curve from which you can find the concentration of an unknown concentration. Doing the same thing at the moment for a level and am a big confused. Thanks
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chibibotto
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Describe how the concentration of a reducing sugar can be estimated without using a colorimeter ?

What about this question? ^

5 marks, OCR
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Lilybyrne
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I could be wrong but I think the only reason you didn’t get the last mark was because you didn’t mention using a centrifuge to collect the supernatant. But overall a brilliant answer!
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15mohsinfa
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(Original post by najeezy)
I sat this paper, but i wasnt happy with the result so i ordered it back and ordered a remark.

Anyways...

heres what i wrote for this question, i was 1 short off full marks for this question.

:

The reducing sugar is first verified that it is a reducing sugar, it is placed in a beaker where benedicts solution is added and it is heated to 80(degrees/celsius) in a water bath. If a reducing sugar is present the solution will change colour from blue to orange-red, this solution is then placed in a curvette/ between a colorimeter and a photoelectric cell, the colorimeter shines a beam of light and the cell picks up the percentage transmission, this is then measure on a calibration cruve with a set of known concentrations, the value can then be read off the curve for its percentage transmission.

Exactly what i wrote, cant beleive that didnt score 6 tbh, but gl with it anyway.
you could have said wear gloves or handle with care as you don't want grease or anything to get on the cuvette as it could affect the results and give you less percentage transmission. Also, I think what you didn't mention is using a red colour light so only that light can go through as red goes through red only and giving you the most accurate result. But otherwise, you should have gotten 6 have you seen the mark scheme or what it said there?
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miin_yoonkii
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I don't think you mentioned how the precipitate needs to be filtered out first
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