a) A circular ring (2.9 cm OD) is used to determine the surface tension of a liq
ID: 527196 • Letter: A
Question
a) A circular ring (2.9 cm OD) is used to determine the surface tension of a liquid. The plane of the ring is positioned so that it is parallel to the surface of the liquid. The ring is immersed in the liquid and then pulled upward, so a film is formed between the ring and the liquid. A total upward force of 1.85 times 10^-2 N is required to lift the ring to the point where it just breaks free of the surface. Given that the mass of the ring is 0.79 g and acceleration due to gravity is 9.81 m s^-2, determine: i) the force due to lifting the ring ii) the surface tension of the liquid iii) the liquid used, using the data provided in Table 1 b) Define the term 'micelle'; explain how such structures form in appropriate systems.Explanation / Answer
a) First finding force then by Du Nouy ring method F= 2 * pi * ( ri + ro ) * Y
where, ri = radius of inner ring of liquid pulled
ro = radius of outer ring of liquid film
Y = surface tension of liquid
Similarly Y can be found by using equation Y = F / (4*pi*r)
Y= 1.85*10-2/(4*3.14*0.0145)
r = 2.9/2 = 0.0145cm
Y = 1.85*10-2/0.182
Y = 0.1016 N/m
b) Micelles are an aggregate of molecules. these molecules are made of hydrophillic part (water loving one) and an hydrophobic part which is hydrocarbobon chain and repell water (water hating part). When these molecules increase in concentration at a particular concentration they form a cluster called micelle. In the cluster which micelle is formed of hydrophillic part called shell outside and hydrophobic part forming a core inside away from water molecules.
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