QUALITY CONTR CONTROL OL I SAMPLE PROBLEMS IN TITRIMETRY AND GRAVIMETRY
PROBLEM 1 How many millimoles of solute are contained in 2.00 L of 2.76 x 10-3 M KMnO4?
5.52 mmol
PROBLEM 2 How many millimoles of solute are contained in 250mL of a solution that contains 4.20ppm of CuSO4?
6.58 x 10-3 mmol
PROBLEM 3 How many milligrams of solute are contained in 26.0 mL of 0.150M sucrose (FW = 342 g/mole)?
1.33 x 103 mg
PROBLEM 4 Calculate the molar concentration of a solution that is 50.0% (w/w) in NaOH and has a specific gravity of 1.52.
19.0 M
PROBLEM 5 Calculate the molar concentration of a dilute HCl solution if titration of 0.2694 g of primary standard Na2CO3 required 38.77 mL of the acid.
0.1311 M
PROBLEM 6 The benzoic acid extracted from 106.3 g of catsup required a 14.76 mL titration with 0.0514M NaOH. Express the results of this analysis in terms of % Na benzoate (144.10 g/mol). 0.1028%
PROBLEM 7 A 25.0 mL aliquot of vinegar was diluted to 250 mL in a volumetric flask. Titration of 50.0 mL aliquots of the diluted solution required an average of 34.88 mL of 0.09600M NaOH. Express the acidity of the vinegar in terms of % (w/v) of CH3COOH. 4.02%
PROBLEM 8 A 0.5843g sample of a plant food preparation was analyzed for its N content by the Kjeldahl method, the liberated NH3 being collected in 50.00 mL of 0.1062M HCl. The excess acid required an 11.89 mL back-titration with 0.0925M NaOH. Determine % N.
10.09% N
PROBLEM 9 Titration of a 0.485g sample by the Mohr method required 36.8 mL of standard 0.1060M AgNO3 solution. Calculate the % Cl- in the sample.
28.5% Cl-
PROBLEM 10 The theobromine (C7H8N4O2) in a 2.95g sample of ground cocoa beans was converted to the sparingly soluble silver salt, C7H7N4O2Ag by warming in an ammoniacal solution containing 25.0mL of 0.0100M AgNO3. After reaction was complete, all solids were removed by filtration. Calculate the % theobromine (180.1 g/mole) in the sample if combined filtrate and washings required a back-titration of 7.69mL of 0.0108M KSCN.
1.02%
PROBLEM 11 Calculate the volume of 0.0500M EDTA needed to titrate 26.37mL of 0.0741M Mg(NO3)2.
39.1 mL EDTA
PROBLEM 12 A 1.509 g sample of a Pb/Cd alloy was dissolved in acid and diluted to exactly 250.0mL in a volumetric flask. A 50.00mL aliquot of the diluted solution was brought to a pH of 10.0 with an NH 4+/NH3 buffer. The subsequent titration involved both cations and required 28.89mL of 0.06950M EDTA. A 2nd 50.00mL aliquot was brought to a pH of 10.0 with an HCN/NaCN buffer, which also served to mask the Cd+2; 11.56mL of the EDTA solution were needed to titrate the Pb +2. Calculate the % Pb and Cd in the sample.
55.16% Pb and 44.86% Cd
PROBLEM 13 The iodine produced when an excess of KI was added to a solution containing 0.1518g of K2Cr2O7 required 46.13mL titration with Na2S2O3. Calculate the molar concentration of the thiosulfate solution.
0.06711 M
PROBLEM 14 Titration of 0.1467g of primary standard Na2C2O4 required 28.85mL of KMnO4 solution. Calculate the normal concentration of KMnO4 in the solution.
0.07590 N
PROBLEM 15 Treatment of a 0.4000g sample of impure KCl with an excess of AgNO3 resulted in the formation of 0.7332g of AgCl. Calculate the % KCl in the sample.
95.35% KCl
PROBLEM 16 A 0.1799g sample of an organic compound was burned in a stream of O2, and the CO2 produced was collected in a solution of Ba(OH)2. Calculate the % of C in the sample if 0.5613g of BaCO3 was found.
