Biochemistry Part I – pH change of an unbuffered solution

Biochemistry

Part I: pH change of an unbuffered solution

1.Load http://chemcollective.org/vlab/102

2.Add a 250 mL beaker to your workspacefrom the stockroom.

 3.Add 10 mL of the protein solution.  (To add something to a beaker drag the solution on top of it until the prompt appears.)Then add 90 ml of water to the solution.Record the pH:_____________________(you find the pH by clicking on the beaker)

4.To the same beaker under strong acids add 10 mL  0.10 M HClfrom the stockroom strong acid solutions. 

Record the pH: _____________________ (you find the pH by clicking on the beaker)

5.What is the change in pH?_______________________________

Part II: pH change of a buffered solution

1.You have available the following:

100.0mL of 1.0 MH2CO3 (weak acid; pKa= 6.4)

100.0mL of 1.0 MNaHCO3(conjugatebase of H2CO3; but also a weak acidpKa=10.3)

100.0 mL of Grey Goose Vodka

100.0mL of 1.0 MNa2CO3(conjugate base of HCO3-)

First, explain whichof the solutions aboveyou would useto make a 1 M Carbonate buffer at pH=6.0Next describe how much of each solution you would useto make a 1 M Carbonate buffer at pH=6.0and indicate the total volume.  Show any calculations

2.Reload the Virtual lab page and create your buffer solution above.  Was your math correct? 

Record the pH:______________________ Acceptable ranges are +/-0.05 pH units

3.Add another beaker to your workspace and add 10 mL of the protein solution. Then add 90 ml of buffer to the solution.

Record the pH___________________

4.To the same beaker add 10 mL  0.10 M HClfrom the stockroom strong acid solutions. 

Record the pH: _____________________ (you find the pH by clicking on the beaker)

5.What is the change in pH?_______________________________

Post lab questions

1.In Part II, if instead of making a 1.00M carbonate solution, you made 0.100 M carbonate solution, how would this effect the change in pHwhen you added 0.1 M HCl to the protein buffer solution? What would be the new pH?  Show your calculations and also use the program. Compare the two results.

2.If you wanted to make a buffer at pH=8.  Would carbonate be a suitable buffer?  Please explain why or why not?

3.Why is it important thatbiochemistry solutions are in buffered solutions?

Explanation & Answer

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