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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