Spa Exam Notes

Practical Ex. 2

Consistent Titration Results:

SPA1/T2

♥ Rinse pipette & burette with relevant solutions ♥ Remove air bubbles in rubber tube of burette ♥ Ensure that the end point is the result of one extra drop of titre ♥ Titrate with constant swirling How to ensure no dilution of solutions to be titrated? Rinse important apparatus (burette, pipette) with the specified chemical. Explain why a conical flask was used and not a beaker.

SPA2/T2

The design of the conical flask has the sloping surface which prevents spilling when swirling. Expt: Crystallization

SPA3/T2

Source of Error: water of crystallization not totally driven off from solid …. Improvement: Make sure even heating by rotating the boiling tube as the heating is being carried out Expt: collecting Co2 liberated Sources of Error: ♥ Gas is lost to the environment b4 the stopper could be placed over the conical flask causing vol of gas collected to be less than expected ♥ Gas evolved is used to displace water in the rubber bung causing the vol of gas collected to be less than expected ♥ Vol of gas may not be measured at 25deg and 1 atm. Hence affecting calculations Improvements:

SPA7/T2

♥ Use dropping funnel to introduce HCL into the flask and subtract the air displaced by the intro of HCL from the experimental vol of gas collected to reflect the actual vol of gas collected ♥ Use a gas syringe (frictionless) to collect the gas instead of using the displacement of water Sources of Error: ♥ Inaccurate measure of limiting reagent using measuring cylinder ♥ Thermometer, with bad precision of 0.5deg

♥ Calorimeter is not insulated Improvements:

SPA1/T3

♥ Introduce with pipette or burette as they have higher precision ♥ Thermometer with 0.1deg precision ♥ Calorimeter with cover and proper insulated Consistent Readings: ♥ Adding Titrant drop-wise near the end point ♥ Constant swirling of solution as Titrant is added Anomalous Readings: ♥ Air bubbles trapped in the burette tip or tubing ♥ Failure to wash down Titrant adhering to the sides of the conical flask which is not mixed with the aliquot Percentage Error of Burette:

SPA3/T3

% Error for Titration= 0.05(2)Titration Reading×100% Anomalous Readings: ♥ Air Spaces in Burette Jet ♥ Solution stuck to the sides of the conical flask Alternative Method to determine End point: The ambiguity in detecting the colour change ( from ____ to______) can be removed by using a pH meter in a datalogger. The pH curve of this titration is plotted for the end point to be determined. This pH meter is calibrated at the pH of the equivalence pH=____