Chapter 4, Problem 157
(d) Balance all equations.
Video transcript
Brass is an approximately 4:1 alloy of copper and zinc, along with small amounts of tin, lead, and iron. The mass per-cents of copper and zinc can be determined by a procedure that begins with dissolving the brass in hot nitric acid. The resulting solution of Cu2+ and Zn2+ ions is then treated with aqueous ammonia to lower its acidity, followed by addi-tion of sodium thiocyanate (NaSCN) and sulfurous acid (H2SO3) to precipitate copper(I) thiocyanate (CuSCN). The solid CuSCN is collected, dissolved in aqueous acid, and treated with potassium iodate (KIO3) to give iodine, which is then titrated with aqueous sodium thiosulfate (Na2S2O3). The filtrate remaining after CuSCN has been removed is neutralized by addition of aqueous ammonia, and a solu-tion of diammonium hydrogen phosphate ((NH4)2HPO4) is added to yield a precipitate of zinc ammonium phosphate (ZnNH4PO4). Heating the precipitate to 900 °C converts it to zinc pyrophosphate (Zn2P2O7), which is weighed. The equations are (1) (2) (3) (4) (5) (a) Balance all equations.
(b) When a brass sample with a mass of 0.544 g was sub-jected to the preceding analysis, 10.82 mL of 0.1220 M sodium thiosulfate was required for the reaction with iodine. What is the mass percent copper in the brass?
(c) The brass sample in part (b) yielded 0.246 g of Zn2P2O7. What is the mass percent zinc in the brass?
On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac-tion. The unbalanced equation is (a) Balance the equation.
On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac- tion. The unbalanced equation is X (b) How many moles of oxide were formed, and how many moles of semimetal were in the initial 0.200 g sample?
(c) What is the identity of the semimetal M?