Free Solutions and Colloids MCQs with Answers

71. Which of these is incorrect:

• A. Some times physical adsorption pass over to chemisorption on increasing the temperature of the system.
• B. Oxygen is adsorbed on charcoal but on desorption it also releases CO and CO2
• C. Only lighter gases show physical adsorption at low temp.
• D. Activation energy of chemisorption > activation energy of physical adsorption

Explanation: All gases show the physical adsorption at low temperature.

72. The colloidal solutions of gold prepared by different methods have different colours due to the:

• A. presence of different types of foreign particles depending upon the method of preparation of the colloid
• B. different concentrations of gold
• C. various forms of gold
• D. presence of different size of the colloidal particles obtained in different methods.

Explanation: Colloidal solutions of gold prepared by different methods have different colors due to the presence of different size of the colloidal particles obtained in different methods.

73. Cloud bursts occur due to one of the following reasons:

• A. the clouds are attracted towards the electrical charge on the earth.
• B. large amount of water is present in the cloud
• C. dense clouds are present in the upper atmosphere
• D. mutual discharge of oppositely charged clouds resulting in the coagulation of water droplets

Explanation: This is due to mutual discharge oppositely charge clouds resulting in the coagulation of water droplets.

74. When a river meets the ocean they generally form delta due to :

• A. Coagulation of sand
• B. sedimentation of common salt
• C. deposition of MgCl2
• D. mutual coagulation

Explanation: Sand is a negatively charged colloidal particles, which is carried by river to the ocean which is a vast reservoir of Na+, Mg+,K+, ion. These cations coagulate sand particles at the meeting point of river and ocean. In this way delta is formed.

75. FeCl3 stops bleeding because:

• A. It seals the blood cell
• B. Blood starts flowing in reverse direction
• C. The blood is coagulated and the blood cell is sealed
• D. None

Explanation: Blood is a colloidal solution of albuminoid substance in water and alubminoid is negatively charged. So opposite charged Fe3+ ion proves a good coagulating reagent for blood.

76. The sky or water in the sea looks blue due to:

• A. disperson effect
• B. scattering
• C. reflection
• D. transmission

Explanation: The sky or water in the sea looks blue because the light of long wavelength gets absorbed, and light of short wavelength (blue light) gets scattered by water and falls on cornea of our eyes.

77. The most commonly used adsorbent for chromatographic separation of organic compounds is :

• A. Silica gel
• B. Alumina
• C. Fuller's earth
• D. Activated charcol

Explanation: The adsorbents commonly employed for chromatography are alumina (specially prepared for this purpose), magnesium oxide, and sucrose. The solvents used are usually organic-acetone, bezene and petroleum ether etc.

78. A freshly prepared Fe(OH)3 precipitate is peptised by adding FeCl3 solution. The charge on the colloidal particles is due to the preferential adsorption of:

• A. Cl− ions
• B. Fe3+ ions
• C. OH− ions
• D. Fe+2 ions

Explanation: Fe(OH)3 is a positive sol. The positive charge is due to the preferential adsorption of Fe3+ ions.

79. Substances whose solutions can readily diffuse through parchment membrane are:

• A. Colloids
• B. Crystalloids
• C. Electrolytes
• D. Non electrolytes

Explanation: Solutions which can diffuse readily through parchment membrane are crystalloids.

80. AgI is used for producing artificial rain because Agl:

• A. Is easy to spray at high altitude
• B. Is easy to synthesizes
• C. Has crystal structure similar to ice
• D. Is insoluble in water

Explanation: AgI has the crystal structure similar to ice. Hence it can act as a nucleus for the precipitation of the water molecules and causes rain.