Worked solutions PK.pdf

# Worked solutions PK.pdf - Worked solutions for Applied...

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Worked solutions for: ‘Applied Colloid & Surface Chemistry’ by R.M. Pashley and M.E. Karaman (J.Wiley, 2004) Chapter 2 1. Answer: Use Laplace equation in the form (eqn 2.8): r P θ γ cos 2 = . Gives pressure of 2 bars. Addition of surfactants will reduce the interfacial tension and hence the pressure. The use of hydrophobic porous materials to prevent water flow is used in clothing and in concentrating orange juice. 2. Answer: the Laplace equation for spherical soap films is r P γ 4 = . Hence we can calculate the pressure difference between each bubble and the atmosphere and therefore between the bubbles. The pressure difference between the two bubbles can then be used in the Laplace equation to obtain the radius (1.5cm) of the (spherical) soap film formed between the bubbles. 3. Answer: Use the capillary rise equation (2.9). Make sure that you convert the parameters to SI units. The calculated surface tension value is: 0.62Nm -1 . 4. Answer: Apply the full Laplace equation to calculate the pressure difference across the water interface, relative to atmospheric pressure. The difference in these two pressures must equal the hydrostatic pressure difference in the water (ie h ρ g). This gives a height difference of 4.1mm. 1

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