1.7 Chemical Assay Calculations 04. 0.300 g of a chromium compound was oxidized to convert chromium to dichromate (Cr20,2). An excess of iodide was added to the acidified solution and the liberated iodine was titrated with sodium thiosulfate (0.1000 mol dm'); 27.00 cm being required. Calculate the % Cr in the compound. Cr20? +61 + 14 H-- 2 Cr* + 7 H:0+3 13 12+2 5,0, 21+25,002- Q5. A sample of calcium chloride was dissolved in water and excess oxalic acid added. The precipitated calcium oxalate was filtered off and re-dissolved in sulfuric acid. The resulting solution was titrated with potassium permanganate, 0.002 mol being required. Estimate the number of moles of calcium chloride present in the original sample. CaCl2 + (COOH)2 Ca(COO)2 + 2 H+ + 2 C Ca(COO) + H2SO4 = Ca?+ + O2 + (COOH)2 5 (COOH)2 + 2 Mno. +6 H = 2 Mn +10 CO2 + 8 H,0 Hint: First decide which are the intermediates. 06. The chromium in a 1.200 g sample of a compound was converted into dichromate and the solution made up to 250.0 cm'. 25.00 cm of 0.1000 mol dm Fe required 27.40 cm the dichromate solution for complete oxidation to Feat. Write down two half- equations for this redox titration and hence calculate % Cr in the compound