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Surface Chemistry Test - 31

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Surface Chemistry Test - 31
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Weekly Quiz Competition
  • Question 1
    1 / -0
    Which of the following types of metals form the most efficient catalysts?
    Solution
    Transition metals can form unstable intermediate products with suitable reactants. These intermediate products lower the activation energy of the reaction which makes the reaction faster. So, transition elements are the most efficient catalysts.
  • Question 2
    1 / -0
    Evaporation is the process which occurs:
    Solution
    In the process of evaporation, molecules present on the surface of the liquid gets converted in its gaseous state hence it is a surface phenomenon.
  • Question 3
    1 / -0
    A emulsifier is a substance which:
    Solution

    Correct Answer: Option A

    Explanation: 

    An emulsifier is a substance that stabilizes the emulsion by increasing its kinetic stability. Examples are egg yolk in which emulsifying agent is lecithin and sodium phosphate.

    Final Answer: An emulsifier is a substance that stabilizes the emulsion. Hence the correct answer is option $$A$$.

  • Question 4
    1 / -0
    Which of the following is an emulsifying agent?
    Solution
    Gum  is an emulsifying agent. Other examples of emulsifying agents include agar, albumin, and casein etc.
    Milk and Butter are examples of emulsion and gel respectively.
    Hence, option (C) is correct answer.
  • Question 5
    1 / -0
    The process of separation of cream from milk is called:
    Solution
    The process of separation of cream from milk is known as demulsification which involves the breaking of an emulsion into two separate liquid layers and can be achieved by centrifugation.
  • Question 6
    1 / -0
    Which of the following is an emulsifier?
    Solution
    An emulsifier consists of a water-loving hydrophilic head and an oil-loving hydrophobic tail. The hydrophilic head is directed to the aqueous phase and the hydrophobic tail to the oil phase. The emulsifier positions itself at the oil/water or air/water interface and, by reducing the surface tension, has a stabilising effect on the emulsion.
    Soap (once dissociated in water) consists of a non-polar hydrocarbon tail and a polar head. The non-polar hydrocarbon tail interacts with non-polar substances through dispersion forces, whilst the polar head interacts with polar substances (normally water) which forms dipole-dipole interactions and hydrogen bonds with water.
    The presence of soap in a mixture of oil/grease and water will create an emulsion upon agitation. The hydrocarbon tails of soap dissolves in the oil and promotes droplet formation. These droplets repel each other, as they have the same net negative charge. These individual droplets can be dissolved in water as they form ion-dipole interactions. Therefore, Soap is an emulsifier.
  • Question 7
    1 / -0
    A negatively charged suspension of clay in water will need for precipitation the minimum amount of:
    Solution
    As the coagulating power of $$Al^{3+}$$ is highest due to high charge and small size, therefore, aluminium chloride will be required in minimum amount to coagulate negatively charged suspension of clay in water. 
  • Question 8
    1 / -0
    When freshly precipitated $$Fe{ \left( OH \right)  }_{ 3 }$$ is boiled with water in the presence of few drops of dil. $$HCl$$, a hydrated ferric oxide sol is obtained. This method is termed:
    Solution
    Freshly prepared ferric hydroxide on treatment with a small amount of ferric chloride in presence of dil hydrochloric acid solution forms a dark reddish brown solution where Ferric chloride acts as a peptizing agent and the process is known as peptization.
  • Question 9
    1 / -0
    The emulsifying agent in milk is:
    Solution
    Casein is the emulsifying agent in milk which keeps two immiscible layers of fat and water together.
  • Question 10
    1 / -0
    Which of the following is not an example of a water-in-oil emulsion?
    Solution
    An emulsifier is a substance that stabilizes an emulsion by increasing its kinetic stability. It stabilize emulsion by reducing the interfacial tension between two liquids to form the emulsion. They are long chain molecules with polar groups.
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