March 16, 2015

10th Physical Science Important Questions and Answers for Public Exams

Q: What is the action of soap particles on greasy cloth? (4 Marks)

A: Soaps and detergents make oil and dirt present on the cloth come out into water, there by making the cloth clean. Soap has one polar end and one nonpolar end. The polar end is hydrophilic in nature and this end is attracted towards water.

The non-polar end is hydrophobic, in nature and it is attracted towards grease or oil on the cloth, but not attracted towards water. When soap is dissolved in water, its hydrophobic ends attach themselves to dirt and remove it from the cloth. The hydrophobic end of the soap molecules move towards the dirt or grease particles.

The hydrophobic ends attached to the dirt particle and try to pull out. The molecules of soap surround the dirt particle at the centre of the cluster and form a spherical structure called micelle. These micelles remain suspended in water like particles in a collidal solution. The various micelles present in water do not come together to form a precipitate as each micelle repells the other because of the ionion repulsion. Thus, the dust particles remain trapped in micelles and are easily rinsed away with water. Hence, soap micelles remove dirt by dissolving in water.

Q: We know metals are arranged basing on their reactivity. What is the name given to that arrangement? How it helps in extraction of metals? (4 Marks)

A: Activity Series: Extraction of the metal from its ore depends on the reactivity of the metal. To understand the order of reactivity of metals
that are very familiar, we study their chemical reactions with cold water, steam, dilute, strong acids and Cl2 and based on their vigorous activity order in these reactions, we frame out activity series.

Arrangement of the metals in decreasing order of their reactivity is known as activity series. Usefulness of activity series in extraction of metals: Simple chemical reduction methods like heating with C, Co etc to reduce the ores of these metals depends mainly on the position of the metal in the activity series. Extration of metals at the top of the activity series can be done by electrolysis. Extraction of metals in the middle of the activity series can be extracted by 

a) Sulphide ores are converted into oxides by roasting.

b) The metal oxides are then reduced to the corresponding metal by using suitable reducing agents like carbon. Extraction of metals at the bottom of the acitivity series by heating alone as they are often found in free state.
Extraction of these metals can also be done by displacement from aqueous solutions.

Q: How do you appreciate the role of Buckminister fullerence in medicine. (2 Marks)

A: Fullerences are under study for potential medicinal use such as specific antibiotics to target resistant bacteria and even target certain cancer cells such as melonoma. This is still under research studies.

I appreciate its usefulness in medicine which may become a good medicine for curing certain cancer in the time to come.

Q: What is the role of esters in everyday life? (2 Marks)
A: Esters are generally volatile liquids with sweet or pleasent smell or fruity smell. Artificial perfumes are made with esters. Esters are used as flavouring agents. Esters are used in making artificial flavours and essences used in ice-creams, sweets, cool drinks... etc. Saponification (soap making) is the alkaline hydrolysis of esters.

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