Analytical Chem istry - DePauw University

536 Analytical Chemistry 2.0Practice Exercise 9.14In an analysis for hardness we treat the sample as if Ca 2+ is the only metalion reacting with EDTA. The grams of Ca 2+ in the sample, therefore, is0.0109molEDTAL2+1 molCa× 0.02363 L×molEDTA= 258 . × 10 −441258 . × 10−2+molCaCO3molCa × ×2+molCa100.09 gCaCO3= 0.0258 gCaCOmolCaCOand the sample’s hardness is0.0258 gCaCO 31000 mg× = 258 mg CaCO3 0.1000 L g/L33molCa 2+Click here to return to the chapter.Practice Exercise 9.15The titration of CN – with Ag + produces a metal-ligand complex ofAg(CN) 2 2– ; thus, each mole of AgNO 3 reacts with two moles of NaCN.The grams of NaCN in the sample is0.1018 molAgNO 32 molNaCN× 0.03968 L×LmolAgNO49.01 gNaCN× = 0.3959 gNaCNmolNaCNand the purity of the sample is0.3959 gNaCN× 100 = 88. 33%w/w NaCN0.4482 gsampleClick here to return to the chapter.Practice Exercise 9.16The total moles of EDTA used in this analysis is0.02011 molEDTALOf this,× 0. 02500 L= 5. 028× 10 −4mol EDTA2+0.01113 molMg× 0.00423 L×L1 molEDTA= 4.708× 10 −5molEDTA2+molMg3