A sample contains palladium, cadmium, and other impurities. The mass percent of palladium and cadmium can be determined using a process that starts with the sample being dissolved in hot nitric acid. Aqueous ammonia is used to lessen the acidity of the resulting solution of Cu2+ and Pd2+ ions, and then sodium thiocyanate (NaSCN) and sulfuric acid (H2SO4) are added to precipitate palladium thiocyanate (PdSCN). The collected solid PdSCN is dissolved in water, treated with potassium iodate (KIO3) to produce iodine, and then titrated with aqueous sodium thiosulfate (Na2S2O3). After PdSCN is removed, the filtrate is neutralized by adding aqueous ammonia. Then, a solution of diammonium hydrogen phosphate ((NH4)2HPO4) is added, resulting in a precipitate of cadmium ammonium phosphate (CdNH4PO4). The precipitate is transformed into cadmium pyrophosphate (Cd2P2O7) by heating it to 900 °C, which is then weighed. The equations involved in the process are:
(1) Pd(s) + NO3—(aq) → Pd4+(aq) + NO(g) (in acid)
(2) Pd4+(aq) + SCN—(aq) + HSO3—(aq) → Pd(SCN)2(s) + HSO4—(aq) (in acid)
(3) Pd2+(aq) + IO3—(aq) → Pd4+(aq) + I2(aq) (in acid)
(4) I2(aq) + S2O32—(aq) → I—(aq) + S4O62—(aq) (in acid)
(5) CdNH4PO4(s) → Cd2P2O7(s) + H2O(g) + NH3(g)
Give the balance equation for each reaction.
