CH 339K Problem Set 1

 

1)      Dihydroxyacetone phosphate (DHAP)and  Glyceraldehyde-3-Phosphate (G3P) are both intermediates in the metabolic breakdown of glucose.  They can be interconverted by the enzyme Triose Phosphate Isomerase.

 

Glycerone-phosphate_wpmp

Biochem_reaction_arrow_reversible_NNNN_horiz_med

D-glyceraldehyde-3-phosphate_wpmp

DHAP

 

G3P

 

For the conversion of DHAP to G3P, DGo = 7.5 kJ/mol

 

a.      Calculate Keq and the equilibrium fraction of G3P at 37o C.

 

b.      What is DG if [G3P] = 1/100 [DHAP]?

           

2)      A Cl- ion is separated from a Na+ ion by a distance of 0.5 nm.  What is the interaction energy (in Joules/mole) in

a.      Water (ε = 78.54)

 

b.      n-Pentane (ε = 1.84)

 

3)      What is the pH of each of the following unbuffered solutions?

a.      0.35 M HCl

 

b.      0.35 M Acetic Acid

 

c.       0.035 M Acetic Acid

 

4)      What is the pH of the following buffer mixtures?

a.      1 M Acetic Acid and 0.5 M Sodium Acetate?

 

b.      0.3 M H3PO4 and 0.8 M KH2PO4?

 

5)      You want a buffer of pH 7, made using KH2PO4 and Na2HPO4:

a.      What is the conjugate acid in this system?  What is theconjugate base?

 

b.      If the buffer is 0.1 M KH2PO4, what must the concentration of Na2HPO4 be?

 

 

c.       You want the same buffer, but with a total phosphate concentration of 0.3 M.  What concentrations of each species do you need?

 

 

 

6)      You have a beaker containing 500 ml of 0.10 M potassium formate buffer pH 3.75.  What is the pH if you add 5 ml of 1.0 M KOH?  (Hint – the change in volume can be ignored)

 

 

 

7)      On my benchtop, I have a jar of the amino acid glycine, a solid powder with MW = 75.07 g/mol.  I also have a bottle of 1 M NaOH, all the distilled, deionized water I can use, and a 2 liter graduated cylinder.  Tell me how to make 2.0 liters of 0.1 M glycine buffer, pH 9.

 

 

 

Useful Physical Constants

 

Constant

Value

Avagadro’s Number

6.02 * 1023

Boltzmann’s Constant

1.3807 * 10-23 JK-1

Charge on electron

-1.602 x 10-19 coulomb

Gas Constant (R)

8.314 JK-1mol-1

Faraday’s Constant

96,485 JV-1mol-1

k = 1/(4pe)

8.99 x 109 Nm2coulomb-2

ln(x)

2.303 log (x)

Dielectric constant of water

78.54