Hydrogen total evolved

A 0.500-g sample of zinc-copper alloy was treated with dilute hydrochloric acid. The hydrogen gas evolved was collected by water displacement at 27°C and a total pressure of 755 mm Hg. The volume of the water displaced by the gas is 105.7 mL. What is the percent composition, by mass, erf the alloy (Vapor pressure of H20 at 27°C is 26.74 mm Hg.) Assume only the zinc reacts. 

The decomposition of powder at an elevated temperature does not differ greatly from that of the nitric esters themselves, i.e. nitrocellulose and nitroglycerine (the decomposition of nitrocellulose at various temperatures was discussed earlier in Vol. II, p. 310). The higher the temperature, the more actively the decomposition of the powder proceeds, with total loss of nitrogen, as NO and N02, and carbon as CO and C02. Hydrogen is evolved chiefly as water, the amount of water decreasing with increase in the temperature of decomposition of the powder (Sapozhnikov s investigations). 

Xylene (100 g., 0.94 mole) is placed in a flask equipped with an efficient reflux condenser and strongly illuminated. To the o-xylene is added slowly 624 g. (200 ml., 3.9 moles) of dry bromine. (Hood.) The temperature of the reaction mixture is increased to about 120° by the time half the bromine is added and then raised gradually to 160° and maintained at this temperature for 2 hours. Loss of xylene by entrainment with the hydrogen bromide evolved may be minimized by packing the reflux condenser with glass beads. With good illumination a total reaction time of 3 hours is sufficient. Any excess bromine is distilled off, and the product is allowed to cool. It is washed with a small amount of chloroform and then recrystallized from chloroform. There is obtained 250-260 g. (74-77%) of tetra-bromo compound, m.p. 116°. 

Chemical analysis shows that for every kmol of A reacted Ikmol of hydrogen is evolved, and that the mol ratio of C to D is 3 to 1. It follows from Eq. (1.31) that to produce 3 kmol of C will require 12g. To this we have to add 6g due to the kmol of by-product D. Finally the 4 kmol of hydrogen will according to Eq. (1.32) account for another 8g, making a total of 26g. Thus one requires 26/3 = 8.7g per kmol of C. Therefore ... 

Kupec et al. [180] determined total sulphur in sludge by a method involving magnesium reduction in which the sample is heated with magnesium powder to convert all sulphur compounds into magnesium sulphide. The magnesium sulphide is treated with sulphuric acid and the evolved hydrogen sulphide determined by iodometric titration. 

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