Unit 4 class notes

Evaluating different ways of estimating purity

Chromatography (TLC)

Advantages
● Simple
● Environmentally friendly
● Cheap
● Quick and easy to produce
● Can visualise impurities by comparing to reference samples

Disadvantages
● Spots are not clearly defined - this may be from human error where too much of
the sample has been used
● Cannot tell you all of impurities present
● Cannot tell you percentage purity
● Stationary phase on plate is very delicate which means that there is a risk of it
breaking easily and have an effect on results
● Interference from contaminations on plate like oils and fingers.



Melting point

Advantages
● Pure substances have a known value to be compared too
● Gives fast results
● Only one piece of equipment required
● Can use data to calculate percentage impurity
● Does not require specialists to operate equipment
● Different substances have different melting point

Disadvantages
● Requires specialist equipment
● More than one substance could have same or similar melting points
● Hard to differentiate
● Hard to see when substance has melted
● Different interpretations
● Non uniform substance