Sodium nitrite, NaNO2, is frequently added to processed meats as a preservative. The amount of nitrite ion in a sample can be determined by acidifying to form nitrous acid (HNO2), letting the nitrous acid react with an excess of iodide ion, and then titrating the I3 - ion that results with thiosulfate solution in the presence of a starch indicator. The unbalanced equations are (1) (2) (a) Balance the two redox equations.

To 100.0 mL of a solution that contains 0.120 M Cr(NO3)2 and 0.500 M HNO3 is added to 20.0 mL of 0.250 M K2Cr2O7. The dichromate and chromium(II) ions react to give chromium(III) ions. (a) Write a balanced net ionic equation for the reaction.

(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?

Sodium nitrite, NaNO2, is frequently added to processed meats as a preservative. The amount of nitrite ion in a sample can be determined by acidifying to form nitrous acid (HNO2), letting the nitrous acid react with an excess of iodide ion, and then titrating the I3 - ion that results with thiosulfate solution in the presence of a starch indicator. The unbalanced equations are (1) (2) (b) When a nitrite-containing sample with a mass of 2.935 g was analyzed, 18.77 mL of 0.1500 M Na2S2O3 solution was needed for the reaction. What is the mass percent of NO2- ion in the sample?

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) Calculate the concentrations of all ions in the solution after reaction. Check your concentrations to make sure that the solution is electrically neutral.