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AS OCR Biology Planning Exercise 2008

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AS OCR Biology Planning Exercise 2008

Postby mariam123 on Tue Apr 15, 2008 4:38 pm

hey! :D
does anyone have this years planning exercise?
thankyou x
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Re: AS OCR Biology Planning Exercise 2008

Postby mariam123 on Fri Apr 18, 2008 3:08 pm

'you are required to plan an investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk'
your planning must be based on the assumption that you are provided with the following:
- rennin solution
- milk
- a solution of sodium citrate
- 1.0 mol dm-3 calcium chloride solution
- school or college laboratory resources

what is the sodium citrate for???
x
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Postby MrMistery on Sat Apr 19, 2008 9:31 am

citrate binds calcium ;)
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Re:

Postby mariam123 on Sat Apr 19, 2008 2:26 pm

MrMistery wrote:citrate binds calcium ;)

thankyou but why are we give this if milk already contains calcium?
x
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Postby MrMistery on Sat Apr 19, 2008 7:57 pm

well, coagulation requires free calcium ions. Calcium ions can't do their job if they're stuck to citrate. By adding more and more citrate you will actually decrease the calcium concentration.
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Re: AS OCR Biology Planning Exercise 2008

Postby mariam123 on Sun Apr 20, 2008 11:53 am

oh yeahhhh lol
cheers=]
xx
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