This assignment focuses on Pore size of membranes measurement. There is also a description of Calculating the activity coefficient of the water.

Pore size of membranes measurement : Calculating the activity coefficient of the water

Chemistry questions

Answer all questions please A(i) (3 marks) The pore size of membranes can be measured by using the decrease in vapour pressure of liquid nitrogen condensed in the pores (i.e. cavities) at low temperatures. Calculate the diameter of the pores in a membrane if at 80.0 K the pressure of N2 gas above the membrane is measured to be 1.310 bar. At 80.0 K liquid nitrogen has the following properties:  = 8.27 mN m-1 Vm = 3.528 x10-5 m3 mol-1 p*vap = 1.369 bar (ii) (2 marks) Water droplets adhere weakly to lotus leaves and but strongly to rose petals, but in both cases the contact angle is ~150o.  Explain, with the aid of diagrams Bi) The partial pressure at 25 °C of the water vapour above a water-ethanol solution for which x(H2O) = 0.5 is 3.7 kPa. The total vapour pressure is 8.7 kPa.

Pore size of membranes measurement : Calculating the activity coefficient of the water

For pure water at 25°C, p*(H2O) = 3.4 kPa; for pure ethanol p*(ethanol) = 4.3 kPa. (i) (1 mark) Calculate the activity and activity coefficient of the water. (ii) (1 mark) Calculate the activity and activity coefficient of the ethanol. (iii) (2 marks) Calculate the molar excess Gibbs free energy when this water-ethanol mixture is made. (d) [4 marks] With the aid perhaps of a diagram, briefly describe osmosis and osmotic pressure. Briefly describe the role of osmosis in preservation of foods such as jams or salted meats. Describe the structure, specificity, reaction mechanism and regulation of one (1) only of the following: (i) A gastric enzyme that works well at pH 2-3. (ii) A gastric enzyme that works well at pH 7.6-8. (iii) A series of enzymes that result in blood clotting.

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