December 3, 2014

Senior Intermediate - Surface Chemistry Important Questions

Q: Explain the terms i) Tyndall effect ii) Brownian movement iii)
Coagulation iv) Electrophoresis.

A: i) Tyndall effect: The phenomenon of scattering of light by
colloidal particles in all directions and formation of bright glowing
cones is called tyndall effect.
ii) Brownian movement: The continuous rapid Zig-Zag movement by
colloidal particles in the dispersion medium.
iii) Coagulation: The phenomenon of lose of charge by a colloidal
solution and coming down as precipitate on addition of electrolyte.
iv) Electrophoresis: The phenomenon of migration of colloidal
particles (+vely charged particles towards Cathode & -vely charged
particles towards Anode) under an applied emf to form precipitate due
to lose of charge.

Q: Explain the terms i) Autocatalysis ii) Gold number iii) Hardy -
Schulze rule iv) Kraft temperature.

A: i) Auto Catalysis: The catalysis in which one of products formed
acts as catalyst.
ii) Gold number: The mass in milligrams (of lyophilic colloid) which
prevents coagulation of 10 ml of gold sol on adding 1 ml of 10% NaCl
iii) Hardy - Schulze rule: The coagulating ability of oppositely
charged ions is directly proportional to the charge of coagulating
iv) Kraft temperature: The temperature above which a micelle is formed.

Q: What is micelle? Explain cleaning action of Soap.
A: Colloidal sized associated particle having hydrophobic end (tail)
and hydrophilic end (head) is called micelle. At critical micelle
concentration, 'ionic micelles' are formed. In Sodium sterate (soap),
sterate ion has C17H35 non polar (tail) part, which dissolves grease
and polar part COO− (head) attracts water to form emulsion. By
washing, spinning, soaking grease containing emulsion washes away with

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