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Question 2 30 marks (a) i) The generation of foam by many cosmetic formulations containing surfactants provide both aesthetic and functional benefits. Describe the conditions that must be met in order for the formation of a foam to take place. 5 marks ii) Describe with the aid of a diagram how the foam structure changes over time after formation. 5 marks iii) Why is any foam thermodynamically unstable? 4 marks iv) Suggest three ways that will prolong the lifetime of a foam 6 marks b) An electrostatic barrier with its characteristic double layer can prevent coagulation of an aqueous dispersion of colloidal particles. i) Sketch a typical electrostatic potential versus distance plot for a flat object with protonated tertiary amine surface groups, when placed in tap water. 4 marks ii) Give TWO different ways to lower the zeta potential of this surface, and sketch on the plot from (question bi above) the effect of each of these on the electrostatic potential as a function of distance. 6 marks