Question

Give scientific explanation

a. Bleaching powder has the odour of chlorine.

b. The hard water of a well becomes soft on adding washing soda to it.

c. Soap forms a precipitate in hard water.

d. The particles of powder are given an electric charge while spraying them to form the powder coating.

e. The aluminium article is used as an anode in the anodising process.

f. When the radiation coming out from certain radioactive substance is passed through an electric field, marks are found at three places on the photographic plate placed in its path.

g A certain type of ceramic tiles are fixed on the outer layer of a space shuttle.

Answer 1

a. When exposed to air, bleaching powder reacts with carbon dioxide in air to produce calcium carbonate and chlorine. Thus, it smells of chlorine.

b. The hardness of hard water is due to the presence of chlorides and sulphates of calcium and magnesium. When washing soda (Na₂CO₃. 10H₂O) is added to the hard water, Na₂CO₃ reacts with the chlorides and sulphates of calcium and magnesium and converts them to insoluble carbonate salts. This changes the hard water into soft water and thus makes it suitable for use.

${{\mathrm{MgCl}}_2}_{\left(\mathrm{aq}\right)}+{\mathrm{Na}}_2{\mathrm{CO}}_{3\left(\mathrm{s}\right)}\to {\mathrm{MgCO}}_{3\left(\mathrm{s}\right)}+2{\mathrm{NaCl}}_{\left(\mathrm{s}\right)}$

c. Soap does not work properly in hard water. This is primarily because hard water contains salts of calcium and magnesium. When soap is added to hard water, it reacts with these salts to form an insoluble precipitate called scum. This scum sticks to the cloth and decreases the cleansing ability of the soap. In addition, soaps do not give lather with hard water.

d. The particles of powder are given an electric charge while spraying them to form the powder coating so that a uniform layer of the powder sticks to the metal surface.

e. The aluminium article is used as an anode in the anodising process to deposit a thick layer of aluminiun oxide,on the article so as to protect the article from further rusting.

f. When the radiation coming out from certain radioactive substance is passed through an electric field, marks are found at three places on the photographic plate placed in its path. These three marks represent the three kind of rays which are emitted by the radioactive substances. One type of radiation deviated slightly towards the negatively charged plate and were called alpha rays. The second type of radiation deviated substantially towards the positively charged plate and was called the beta rays. The third type of radiation did not deviate at all and was called the gamma rays.

g. Certain types of ceramic tiles are fixed on the outer layer of a shuttle because they posess properties like they can withstand high temperatures without decomposing. They are water resistant and electric insulators.