Chemistry 230 lab exam 2 questions with complete solutions.

Anion 1st step separating SO4(^2-) from Cl- and NO3- correct answer: *add ammonia and Ba(OH)2 *foms a white precipitate Ba(^2+) + SO4(^2-)-->BaSO4 (s) Anion 2nd step confirming SO4(^2-) correct answer: *make solution acidic with HNO3 *precipitate stays to confirm SO4(^2-) BaSO4 (s) + H(^+) --> no reaction anion 3rd step confirming Cl- correct answer: *acidify with HNO3 *add AgNO3 to make precipitate *dissolve with ammonia AgNO3 + Cl- --> AgCl(s) + NO3(^-) (aq) (forms precipitate) AgCl(s) + 2NH3 --> Ag(NH3)2(^+) + Cl- (dissolves precipitate) Anion 4th step Confirming NO3(^-) correct answer: *acidify *add FeSO4 mix and H2SO4 *forms dark brown ring in middle cation flame test correct answer: K+ --> lavender flame Ca(^2+) possible --> red flame C step 1 confirming NH4(^+) correct answer: *add NaOH *forms a gas and seen on litmus paper turning blue NH4(^+) +OH(^-) --> NH3(g) + H2O C step 2 separating Pb(^2+) correct answer: *add HCl *ice bath to accelerate the precipitation of PbCl2 by decreasing the solubility of PbCl2(^-) *adding too much HCl will cause PbCl4(^2-) to form and PbCl2(^-) will not precipitate Pb(^2+) + 2Cl(^-) --> PbCl2 (s) C 3rd step Confirming Pb(^2+) correct answer: *heat solution *add Na2S creating a heavy black precipitate