Analytical Chem istry - DePauw University

408 Analytical Chemistry 2.0Of the three choices, the greatest sensitivity is obtained with Fe 2 O 3 becauseit provides the largest value for k.Click here to return to the chapter.Practice Exercise 8.6From 100–250 o C the sample loses 13.8% of its mass, or a loss of0. 138× 130. 35 g/mol=18.0 g/molconsistent with the loss of H 2 O(g), leaving a residue of MgC 2 O 4 . From350–550 o C the sample loses 55.23% of its original mass, or a loss of0. 5523× 130. 35 g/mol=71.99 g/molThis weight loss is consistent with the simultaneous loss of CO(g) andCO 2 (g), leaving a residue of MgO.We can analyze the mixture by heating a portion of the sample to 300 o C,600 o C, and 1000 o C, recording the mass at each temperature. The loss ofmass between 600 o C and 1000 o C, Dm 2 , is due to the loss of CO 2 (g) fromthe decomposition of CaCO 3 to CaO, and is proportional to the mass ofCaC 2 O 4 •H 2 O in the sample.1 molCO 146.11gCaC OiHO22 4 2gCaC O i H O = ∆m × ×2 4 2244.01 gCO molCOThe change in mass between 300 o C and 600 o C, Dm 1 , is due to the lossof CO(g) from CaC 2 O 4 •H 2 O and the loss of CO(g) and CO 2 (g) fromMgC 2 O 4 •H 2 O. Because we already know the amount of CaC 2 O 4 •H 2 Oin the sample, we can calculate its contribution to Dm 1 .1 molCO( ∆m 1) = gCaC O iH O××Ca 2 4 2146.11gCaC O iH O22 42228 . 01gCOmolCOThe change in mass due to the decomposition of MgC 2 O 4 •H 2 O( ∆m ) = ( ∆m ) −( ∆m)1 Mg1 1 Caprovides the mass of MgC 2 O 4 •H 2 O in the sample.gMgC O i H O = ( ∆m ) ×2 4 2 1 Mg1 mol(CO + CO ) 78. 02 g(CO + CO )22×130.35gMgC OiHO1mol (CO+CO )2 4 2Click here to return to the chapter.2