26 VETERINARY STATE BOARD 



Test: Add a solution of starch paste, when an intensely blue 

 color is produced. 



Give the source and the preparation of iodine. 



Iodine was previously obtained from the ashes of sea-weeds which 

 are treated with water and the solution thus obtained is heated with 

 manganese dioxide and sulphuric acid. Iodine is set free by dis- 

 tillation. 



At present, it is obtained from NalOg, a by-product in the manu- 

 facture of Chili saltpetre. 



Mention the important uses of iodine. 



Used in medicine, photography and in the preparation of aniline 

 dyes. 

 Give the method of making potassiixm iodide. Write the equation 

 involved. 

 Add iodine crystals to an aqueous solution of caustic potash 

 until saturated, then evaporate to dryness; the residue, which con- 

 sists of potassium iodide and iodate, is then strongly heated to 

 decompose the iodate, thus forming iodide with the liberation of 

 oxygen. Dissolve the mass in water and evaporate, when crystals 

 of potassium iodide will be left. 



6K0H -f 31^ = SKI + KIO3 + 3H,0. 

 2KIO3 + heat = 2KI -f SO^. 



What are the phyical and chemical properties of chlorine. Mention the 

 uses and important compounds of chlorine. 



Chlorine is a greenish-yellow gas, two and one-half times heavier 

 than air, and having a highly irritating odor ; soluble in water and 

 convertible into a liquid by cold and pressure. It has a strong 

 affinity for other elements and forms a number of important com- 

 pounds. Its atomic weight is 35.18. 



Uses : Strong disinfecting, deodorizing and bleaching agent and 

 its compounds are valuable medicinal agents. 



Among its important compounds are: sodium chloride, hydro- 

 chloric acid, chloral hydrate, calcium chloride, etc. 

 Describe a method of preparing chlorine and write the reaction. 



Mix manganese dioxide with hydrochloric acid in a large flask 

 provided with a delivery tube and heat gently; chlorine gas wiU be 

 evolved. 



MnO, + 4HC1 = MnCl, + CI, + 2H,0. 

 Describe the preparation of hydrochloric acid. 



It is prepared by the action of sulphuric acid on sodium chloride 

 in the presence of heat. 



2NaCl -f H,SO, = Na,SO, + 2HC1. 



