REPLACEMENT OF NITROBENZENE BY SOYBEAN OIL AS A PROPOSAL FOR THE TEACHING OF THE VOLHARD METHOD IN QUANTITATIVE ANALYSIS
Volhard method is extensively employed in the teaching laboratories of classical quantitative analysis to chloride determination and is based on the reaction of Ag+ with Cl- and Ag+ residual titration with SCN-. Its drawback is that SCN- reacts with the AgCl(s) initially formed. Nitrobenzene is used to avoid this stripping, but it is toxic to the environment and causes problems in final disposal. This work proposed the use of soybean oil as an alternative to nitrobenzene. The traditional and modified methods were applied in the standardization of 0.05 mol L-1 KSCN solution employing 0.05000 mol L-1 NaCl standard and the proposed modification did not affect the results obtained (α = 0.05). No significant differences were observed in the variances and NaCl recovery percentage in the titration of aliquots of 5.00 to 15.00 mL of solution of this salt. The recovery percentages obtained with soybean oil on the titration of synthetic 0.07000 mol L-1 NaCl samples diluted 1:1 to 1:100 were equivalent and even better than with nitrobenzene. The chloride determination in samples of saline, whey cheese, sea water and olive brine obtained by the modified method was satisfactory when compared to the official method with relative errors below 3%.