QUESTIONS. Calculate the percentage composition of the following compounds : 119. Water 120. Potassium chlorate 121. Mercury monoxide 122. Potassium nitrate 123. Sodium nitrate... 124. Barium sulphate. 125. Calcium carbonate 126. Silver chloride . 127. Magnesium pyrophosphate. 128. Potassium platinum chloride 129. Sodium thiosulphate. 130. Magnetic oxide of iron 131. Hausmannite . 132. Copper pyrites 133. Stromeyerite 134. Stilbite 135. Idocrase. 136. Spodumene 137. Sphene 138. Pyromorphite 139. Ethyl alcohol 140. Cane sugar 141. Xylene H2 O. K CI 03. Hg O. KNO3. Na N Ŏ3. Ba S O4. Ca C O 3. Ag Cl. Cu, S+Fe2 S3. Ca O Al, O. 6 Si O +5 H2O. 9 (2 Ca O. Si O1) . 2 (2 Al2O3. 3 Si O2). 3 (Li2 O. Si O2). 4 (Al2O3. 3 Si O2). Ca Si O3. Ca Ti O3. 3 Pby P2 Og. Pb Cl2. C2 H2 Ó. H6 C12 H22 O11. 8 C1 H10 142. Cymene. C10 H14 C2 H5. C2 H5. C2 H5. C2 H5 C2 H2 K O S. K1 Fe Co No. CHEMICAL EQUATIONS; TO CALCULATE THE AMOUNT OF MATERIAL REQUIRED TO PRODUCE A GIVEN WEIGHT OF ANY SUBSTANCE OR THE QUANTITY OF THE SUBSTANCE PRODUCED BY THE DECOMPOSITION OF A KNOWN WEIGHT OF THE MATERIAL. Chemical equations :--The results of any chemical actions are represented by equations in which the signs + and = are used in the same sense as in algebra, so far as regards the weights of matter represented by the symbols. The meaning of such an equation will be best shown by examples. 1. H2SO4 + BaCl2 = BaSO4 + 2 HCI. This equation indicates not only that sulphuric acid and barium chloride react to produce barium sulphate and hydrochloric acid, but, further, that the molecular weight of sulphuric acid reacts with the molecular weight of barium chloride to produce the molecular weight of barium sulphate and twice the molecular weight of hydrochloric acid; hence 98 parts by weight of sulphuric acid react with 208 parts by weight of barium chloride to form 233 parts by weight of barium sulphate and 73 parts by weight of hydrochloric acid gas. The number of atoms of each element must be the same on either side of the equation, consequently the total number of atoms must be the same on either side. The numbers of molecules before and after a reaction are not necessarily the same. 2. H2+ Cl2 = 2 HCl. Here, as in (1), it is indicated that 2 parts by weight of hydrogen combine with 71 parts by weight of chlorine to produce 73 parts by weight of hydrochloric acid. But the equation signifies more: as we know the molecular weights of all the reacting bodies and products it shows that a molecule of hydrogen combines with a molecule of chlorine to form two molecules of hydrochloric acid gas. If we state the molecular weights in grams we know from the equation that 224 litres of hydrogen combine with 22.4 litres of chlorine to yield 448 litres of hydrochloric acid, for two grams of hydrogen measure 224 litres approximately at the standard conditions and, by Avogadro's hypothesis, equal numbers of molecules under the same conditions occupy equal volumes. EXAMPLES. 1. How much oxygen can be obtained by the decomposition of 100 grams of mercury monoxide? The symbol for mercury monoxide is HgO: hence its molecular weight is 216. Hg When mercury monoxide is heated, it is completely resolved into oxygen and metallic mercury, 2Hg O= 2Hg + O2 432 parts of mercury monoxide giving 400 of mercury and 32 of oxygen. If, therefore, 32 grams of oxygen are evolved by the decomposition of 432 grams of mercury monoxide, how many grams of oxygen will be evolved by the decomposition of 100 grams of mercury monoxide? 432 100 :: 32 : x. x = 7.407. 7'407 grams of oxygen will therefore be evolved on heating 100 grams of mercury monoxide. 2. I want 100 lbs. of oxygen: how many lbs. of potassium chlorate must I take? The formula of potassium chlorate is KCIO3. Its molecular weight is therefore This substance on being heated eventually decomposes into potassium chloride and oxygen. That is, 96 lbs. of oxygen are evolved on heating 245.2 lbs. of potassium chlorate. Then how many lbs. of potassium chlorate are required to yield 100 lbs. of oxygen? 96 100 245°2 : x. x = 255'4 lbs. Hence it would require 255°4 lbs. of potassium chlorate to yield 100 lbs. of oxygen. 3. How many cubic centimetres of oxygen and hydrogen, measured at 10 ̊C. and 770 mm. pressure, can be obtained by the decomposition of 1 gram of water? The symbol for water is H2O, its molecular weight is 18. The weight of hydrogen yielded by a gram of water is 1000 cubic centimetres of hydrogen at o° C. and 760 mm. weigh o'08936 grams. Then what volume would o'IIII gram of hydrogen occupy? 0*08936 01III :: 1000: x. x = 1243 28 c.c. of hydrogen. This at 10 and 770 mm. would measure 273 273 +10 :: 1243'28 : a: 770: 760 x. x = 1272'09 c.c. 1000 cubic centimetres of oxygen at o° C. and 760 mm. weigh (16 x 0.08936 gram) = 1'42976 grams. volume would o8889 grams occupy? 142976 08889 :: 1000 x. Then what x = 621713 c.c. of oxygen. This at 10° C. and 770 mm. would measure Therefore, a gram of water on being decomposed would yield at 10° C. and 770 mm. pressure, 1908 206 c.c. of mixed gases consisting of 149. How much potassium chlorate is needed to furnish I lb. of oxygen? 150. I require 2 kilograms of oxygen: how much (a) mercury monoxide, (b) potassium chlorate, (c) manganese dioxide, (d) sulphuric acid, shall I need? 151. On completely decomposing by heat a certain weight of potassium chlorate, I obtain 20°246 grams of potassium chloride. What weight of potassium chlorate did I take, and how much oxygen was evolved? 152. A gas bag has a capacity of 45 litres: how much manganese dioxide containing 70 per cent. of Mn O2 is required to fill it with oxygen at 15° C. and 760 mm. barometric pressure? 153. 132 74 kilograms of hydrogen are needed to inflate a balloon. What weight of zinc and sulphuric acid will be required to produce this quantity of gas? |