This document explores the preliminary calculations of concentration and concentration units, highlighting the discrepancies between calculated and titrated values. It delves into the factors contributing to these discrepancies, including imprecision due to glassware, environmental conditions, and the titration method. A must-read for students and professionals in chemistry and related fields.
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[...] Concentration and Concentration Units PRELIMINARY CALCULATIONS Solution A : Solution B : Solution C : TABLEAU I Calculs and measures Solution A Solution B Solution C pesée calculated (mol ? ?mol) calculated (mL ? Weight for solutions B and C calculated (mL ? ?mL ( measured for solution calculated for solutions B and (mL ? Examples of calculations: calculated from solution . calculated for solution calculated for solution calculated for solution TABLEAU II Solution Volume of titrant (HCl) added (mL ? 1er titrage 2e titrage 3e titrage Average calculated A B C Concentration of the titrant (without uncertainties) Concentration of HCl indicated on the bottle of mother solution (in Concentration of HCl of the mother solution converted in mol/L. [...]
[...] The observed discrepancy may be due to several factors: - The imprecision due to the use of glassware: in addition to the uncertainty related to the graduation, it is possible that small quantities of liquid remain trapped in the glassware during transfers (from a pipette to an Erlenmeyer flask for example). - The imprecision due to environmental conditions: ambient pressure and temperature can affect the properties of the elements involved in the reactions (e.g. density), but also some elements can react when passing through the air. - Finally, there is the imprecision related to the titration method in determining the moment of the 'turning point' and which allows to determine the volume of titrant at equivalence. [...]
