Extended Essays 2021

Evaluation

Random Errors

Limitation: During the refinement process the synthesised solution was ‘dried’ of water

molecules by adding 5g of anhydrous magnesium sulphate ( 4 ) . In the original method, the solution was to be shaken for 5 minutes then left to stand for at least half an hour. However, in

some instances a trial was not able to be completed within one continuous session. Consequently,

the solution with the drying agent would be left to stand for much longer than the half an hour or

even overnight. This random error could have directly affected the concentration of the final

product, due unequal for the agent to react with the water in the solution to form the hydrated

4 precipitate. Improvement: The duration of the reaction between the solution and drying agent could have

been controlled to 12 hours for instance, to allow for more flexibility while still controlling the

duration for more accurate data.

Limitation: A fter the separation of the aqueous layer and the ‘drying’ of the so lution, there is a

random uncertainty associated with any left-over residue of the synthesised solution being stuck

to the walls of the various glassware at these points in the refinement stage.

Improvement: After the separation of the aqueous layer, a small amount of water could have

been used to ‘wash’ the used separating funnel, as the water added would have been ‘dried’ in

the next step when the solution was exposed to the magnesium sulphate. After transferring to the

funnel after drying, the volumetric flask used could have then been washed with a controlled volume of ethanol (7 3 ) . This is because as a solvent ethanol does not affect the measurement

of absorbance value of the solution. Using ethanol at this point, would also remove the need to

use ethanol at the final steps of the procedure.

Limitation: The reflux time was controlled using the stopwatch. This accounted for an

approximate uncertainty approximately of ±2 minutes (0.03 hours) (reaction time of stopping &

reacting the stopwatch/alarm and turning on/off the reflux system). The uncertainty in reflux time

directly affects the concentration of the product, the error ranging from 1%-3% (Appendix #14) .

Improvement: Another alarm could have been set prior to the desired duration, ensuring that at

the exact time, I was prepared to turn off the reflux system.

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