Question

What are the systematic and random errors that occurs during the gravimetric titration for the analysis of the iron pill?

Answer 1

Random error describes errors that fluctuate due to the unpredictability or uncertainty inherent in your measuring process, or the variation in the quantity you’re trying to measure.

A systematic error is one that results from a persistent issue and leads to a consistent error in your measurements. For example, if your measuring tape has been stretched out, your results will always be lower than the true value. Similarly, if you’re using scales that haven’t been set to zero beforehand, there will be a systematic error resulting from the mistake in the calibration

The main difference between systematic and random errors is that random errors lead to fluctuations around the true value as a result of difficulty taking measurements, whereas systematic errors lead to predictable and consistent departures from the true value due to problems with the calibration of your equipment. This leads to two extra differences that are worth noting.

In gravimetric method, the iron content was determined through multiplying the stoichiometric moleratios of Fe2+ ions and multiplying it with the relative atomic mass of Fe. However, there is wasunderlying assumption that the ferrous sulphate in the tablets consisted of only of Fe2+ions which would all be oxidized to Fe3+ with KMnO4. During the manufacturing or storage process, someFe 2+may have been oxidized (or rusted) into Fe3+ ions.

Random errors

Gravimetric errors leading to higher mass of precipitate and, consequently, a higher %w/w:

1) Did not dry the precipitate completely.
2) Did not wash the precipitate with water to remove water soluble species such as those used to cause the precipitation.
3) Incorrectly weighed sample (e.g. fertilizer) and recorded a lower mass value than the real value - leads to a higher %w/w.
4) Other human errors such as writing down balance values incorrectly.

Gravimetric errors leading to lower mass of precipitate and, consequently, a lower %w/w:

1) Incomplete precipitation reaction due to reasons such as not adding enough precipitating agent, not waiting long enough for reaction completion, precipitation performed at a low temperature (slow rate of reaction).
2) Not cooling reaction before filtration of precipitate as at higher temperature the precipitate will give better solubility.
3) Incomplete collection of precipitate due to reasons such as spilling precipitate or not completely collecting precipitate.
4) Incorrectly weighed sample (e.g. fertilizer) and recorded a higher mass value than the real value - leads to a lower %w/w.
5) Other human errors such as writing down balance values incorrectly.

Systematic eroors

1.The small size of the Fe(OH)3 being filtered and the wet medium resulted in some of it sticking on the sides of the filtering funnel. Funnel showed be washed to retrieve the residue, a process should be repeated many times. In addition, due to small size of Fe (OH)3 the process should be repeatedly filter the precipitate solution in order to get asmuch residue possible. However, there may still be traces of Fe(OH)3 unfiltered or stuck inthe filtering funnel which would affect my calculations. To improve, finer filter paper should be used in order to get more iron residue as more Fe(OH)3 would be filtered.

2.There also may have been other impurities and substances that could have adhered to the filtered Fe(OH)3, possibly making result larger than what it should be.

3. Despite taking a reading of the weight of filter paper only when the weight has been constant after continuously drying it in an oven, there may still be inaccuracies in measurement. Since one cannot put the filter paper on the digital balance while it is still hot straight from the oven, the process of leaving it to cold down may have increased the weight it has. Water vapor from air may have added on to the weight of the filter paperduring the wait. This would make measurement larger due to an increased weight. To improve, the paper could have been put in a desiccator to stay dry while it cools down.