This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Surface Chemistry – Emulsions”.
1. An emulsion is a type of colloid.
Explanation: An emulsion is a colloidal dispersion in which both the dispersed phase and the dispersion medium are liquids. It is a suspension of two liquids that usually do not mix. These liquids that do not mix are said to be immiscible.
2. Which of the following is an example of an emulsifier?
Explanation: To obtain a stable emulsion, sometimes, small quantities of certain other substances are added during its preparation. The substances thus added to stabilize the emulsions are called emulsifiers or emulsifying agents.
3. Which of the following is not an example of a water-in-oil emulsion?
a) Cod liver oil
c) Cold cream
Explanation: In an emulsion of water-in-oil (w/o), water is the dispersed phase and oil is the dispersion medium. Cod liver oil, butter and cold cream are all examples of the water-in-oil type of emulsions.
4. Soaps are emulsifying agents.
Explanation: Soaps are sodium or potassium salts of higher fatty acids, for example, sodium palmitate (C15H31COONa), sodium stearate (C17H35COONa), etc. A molecule of soap consists of two parts, the hydrophobic part (soluble in oil) and the hydrophilic part (soluble in water).
5. What is the difference between vanishing cream and cold cream?
a) Both are examples of oil-in-water emulsions
b) Vanishing cream is an oil-in-water emulsion whereas cold cream is a water-in-oil emulsion
c) Vanishing cream is a water-in-oil emulsion whereas cold cream is anoil-in-water emulsion
d) Both are examples of water-in-oil emulsions
Explanation: Vanishing cream is an oil-in-water emulsion, that is, oil is the dispersed phase and water is the dispersion medium. Cold cream is a water-in-oil emulsion, that is, water is the dispersed phase and oil is the dispersion medium.
6. Which of the following is not a method to test the type of emulsion?
a) Microscopic method
b) Conductance method
c) Coagulation method
d) Dye method
Explanation: Coagulation or precipitation is a process of aggregating together the colloidal particles to change them into large-sized particles which ultimately settle as a precipitate. The different methods to test the type of emulsion are-microscopic, conductance and dye method.
7. Which of the following statements regarding emulsions is false?
a) Emulsions cannot be separated into their constituent liquids
b) Emulsions show Brownian motion
c) Emulsions show Tyndall effect
d) Emulsions exhibit properties like Electrophoresis and Coagulation
Explanation: Emulsions can be separated into their constituent liquids by boiling, freezing, centrifuging, electrostatic precipitation by adding large amounts of the electrolyte to precipitate out the dispersed phase or by chemical destruction of the emulsifying agent.
8. Which of the following statement about emulsions is true?
a) Oily drugs cannot be prepared in the form of emulsions
b) Digestion does not involve the process of emulsification
c) Disinfectants like Dettol and Lysol give emulsions of water-in-oil type on mixing with water
d) The cleansing action of soap is based upon the formation of water-in-oil emulsion
Explanation: The digestion of fats in the intestines takes place by the process of emulsification. A small amount of the fat reacts with the alkaline solution present in the intestines to form a sodium soap.
9. What is the emulsifier present in milk that makes it stable?
c) Lactic acid bacillus
Explanation: The emulsifier or emulsifying agent present in dairy emulsions is Casein. Casein is a slow-digesting dairy protein that people often take as a supplement.The most common form of casein is sodium caseinate.
10. What is the dispersion of a liquid in another liquid called?
Explanation: The dispersion of a liquid in a solid is called gel. The dispersion of a gas in a liquid medium is called foam. The dispersion of a liquid in another liquid is called emulsion. The dispersion of a solid or liquid in a gaseous medium is called aerosol.
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