This set of Chemistry Online Test for Schools focuses on “Surface Chemistry – Colloids Around Us”.
1. Colloids are responsible for the blue colour of the sky and sea water.
Explanation: There are a lot of suspended impurities in the atmosphere and sea water that act as colloids. Due to Tyndall effect and Rayleigh scattering, these colloidal particles scatter blue light and hence, make them appear blue in colour.
2. Which of the following statements is incorrect?
a) Clouds are colloidal systems
b) Fog is a colloidal system
c) Mist is a colloidal system
d) Clouds are not a colloidal system
Explanation: When it is cold, the moisture in the air condenses on the surface of dust particles, forming tiny droplets. These droplets are colloidal in nature and form a blanket of fog or mist in the atmosphere. Clouds are colloidal systems as they are aerosols consisting of water droplets suspended in air.
3. Which of the following can be used to cause artificial rain?
a) Silver nitrate
b) Silver iodide
c) Silver chloride
d) Silver sulphate
Explanation: Clouds can be made to cause rain by spraying oppositely charged colloidal dust, sand particles or precipitates of silver iodide over them. This causes a neutralisation reaction between the two colloids and result in the coagulation of water droplets which come down as rain.
4. Presence of colloids helps in sewage disposal.
Explanation: Colloidal particles present in sewage such as dirt, mud have an electrical charge. When sewage is through plates at a high potential, the colloidal particles coagulate due to electrophoresis and gets removed.
5. What is the role of Argyrol?
a) It is used to cause artificial rain
b) It is used as a lubricant
c) It is used as an eye lotion
d) It is used as an antacid
Explanation: Argyrol is an antiseptic containing solutions of mild silver proteins. It is made up of a silver sol and is used as an eye lotion majorly to treat gonorrhoeal blindness and other pathogenic infections in the eyes of new-born infants.
6. Which of the following diseases is cured using colloidal antimony?
Explanation: Most of the medicines used today are of colloidal forms as they are easy to assimilate in the body. Colloidal antimony is usually used to cure eye diseases and also Kalaazar(also called visceral leishmaniasis).
7. What is “aquadag”?
a) Colloidal solution of graphite in water
b) Colloidal solution of oil in water
c) Colloidal solution of silver in water
d) Colloidal solution of gold in water
Explanation: Aquadag is the trade name of a colloidal solution of graphite in water. It is mainly used as a conductor and a lubricant. On the other hand, a colloidal solution of oil in water is called as “oildag” and a colloidal solution of gold in water is called “Purple of Cassius”.
8. What is the application of a colloidal solution of silver bromide in gelatine?
b) Rubber industry
c) Leather industry
Explanation: A colloidal solution of silver bromide in gelatine is used in photographical devices. The colloidal solution is applied on glass plates, celluloid films or paper to form sensitive plates in photography.
9. Which of the following can be used in place of tannin for the process of tanning?
a) Zinc salts
b) Copper salts
c) Chromium salts
d) Cobalt salts
Explanation: Tannin, obtained from plants, is a mixture of polyhydroxy benzoic acids. It contains negatively charged colloidal particles which make it useful for tanning as animal hides contain positively charged colloidal particles. Chromium salts can be used in place of tannin.
10. Which of the following is used to cure arsenic poisoning?
a) Colloidal solution of zinc hydroxide
b) Colloidal solution of ferric hydroxide
c) Colloidal solution of chromium hydroxide
d) Colloidal solution of calcium hydroxide
Explanation: Colloidal solution of ferric hydroxide (Fe(OH)3) is given to a person suffering from arsenic poisoning. It is used as ferric hydroxide adsorbs arsenic and this can be vomited out later.
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