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108. What is the weight of one litre of iodine vapour at N.T.P.? Give the volume of hydrogen and of air which would weigh the same as the iodine.

109. How much sulphuric acid and manganese dioxide would be needed to liberate all the iodine from 379 grammes of potassium iodide?

110. Four thousand three hundred and twenty-one c.c. of chlorine at N.T.P. were required to liberate all the iodine from a solution of potassium iodide. How much of this salt was present?

111. How is iodine tested for when in the free state? How is it detected when in combination ?

112. Name the impurities usually present in commercial iodine and state how it may be obtained chemically pure.

113. To an aqueous solution of potassium iodide and starch, chlorine water is added drop by drop. What occurs ? On adding excess of chlorine water what takes place ? Explain both reactions.

114. Chlorine, bromine, and iodine are separately added to solutions of (a) potassium iodide, (6) potassium bromide (c) potassium chloride. What occurs in each case ?

115. 0-5205 gramme of an oxide of manganese was treated with hydrochloric acid and the evolved chlorine was led into solution of potassium iodide. The liberated iodine required 165-4 c.c. of a standard solution of sodium thiosulphate, of which i c.c. was equal to o‘005 gramme iodine. Find percentage of manganese dioxide in the oxide.

116. One hundred and nineteen grammes of iodine are suspended in water. What volume of chlorine at N.T.P. will be required to convert all the iodine into iodic acid ?

117. Seventy-three c.c. of a solution of iodine (containing 1247 grammes per litre) were added to a mixture of sulphuretted hydrogen and starch before a permanent blue coloration was obtained. Find the amount of sulphuretted hydrogen present.


118. Give the names and formulæ of the chief minerals containing fluorine, and name substances in which it is always found in minute quantity.

119. Describe the various attempts which have been made to isolate fluorine.

120. What is the action of flucrine on (a) hydrogen, (6) water, (c) platinum, (d) silica ?

121. Find the percentage of fluorine in fluor spar and cryolite.

122. How may the presence of fluorine in a compound be ascertained ?

123. Give the formulæ of the fluorides of (a) hydrogen, (6) silver, (c) silicon, (d) boron, (e) calcium, (f) potassium.

124. Berzelius found that when 100 parts of calcium fluoride were heated with sulphuric acid till completely decomposed, 175 parts calcium sulphate were obtained. Calculate the atomic weight of fluorine from these data. Later experiments gave 174'5 parts calcium sulphate. Calculate the atomic weight from this result.

125. 362617 grammes of calcium fluoride when treated with strong sulphuric acid, yielded 56867 grammes of calcium sulphate. From these data calculate the atornic weight of fluorine.



126. How does oxygen occur in the free state and in the combined state in nature ?

127. What proportion of (a) air, (6) water, (c) the earth's crust, consists of oxygen ?

128. By whom was oxygen discovered, and in what year? Who discovered it independently, and when ?

129. What name was given to oxygen by its discoverer ? Who proposed the name oxygen, and for what reasons ?

130. From what substance was oxygen first prepared ? Describe the form of apparatus originally used, and state how the experiment would be made now.

131. Express by equations the reactions which occur when (a) potassium chlorate, (6) mercuric oxide, (c) manganese dioxide, are strongly heated.

132. Why is manganese dioxide generally mixed with potassium chlorate for the preparation of oxygen ?

133. What impurity is always present in oxygen prepared by heating a mixture of potassium chlorate and manganese dioxide ? How may this impurity be removed ?

134. Name six oxides which when simply heated lose oxygen. Express each reaction by an equation.

135. How may oxygen be obtained from each of the following bodies ?-(a) water, (6) sulphuric acid, (c) potassium bichromate, (d) bleaching powder.

136. How may oxygen be obtained from potassium manganate and from potassium permanganate ?

137. Describe fully any process for obtaining oxygen from the air,

138. What processes have been proposed for obtaining continuous supplies of

oxygen from the air ?

139. How may oxygen be obtained from (a) lime, (6) ferric oxide, (c) silica, (d) nitric acid ?

140. Give two distinct methods for the preparation of oxygen from water, and sketch the apparatus necessary for each.

141. Find the percentage of oxygen contained in each of the following substances :-(a) water, (6) potassium

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