Question

compare these different methods for determining the concentration of copper(II): titration, quantitative precipitation, and spectroscopy and discuss the applicability (under what conditions would each be preferable) of each method.

Answer 1

COMPLEXOMETRIC TITRATIONS

A complex is formed by the reaction between ions and molecules which are capable of independent existence. Complexometrc titration is where a metal ion (in this case, Cu (II)) is titrated with a chelating agent, until at the end point it is fully complexed. An indicator is used to determine the end point.

Complexometric titrations are reliable and accurate (if done properly of course). Usually complexometric titrations are done with EDTA, which allows a wide avariety of metals to be analysed, even with the presence of completing complexing agents such as ammonia. Although there are automatic titrators, a majority of the titrations are done manually. This may cause errors.

PRECIPITATION TITRATIONS

Precipitation is when the cationic and anionic species of a solution, react to form an insoluable solid, depending on the solubility. Precipitation titrations are reactions where a slightly soluable solid which precipitates, is formed. For Cu(ii), the formation of CuCO₃ can be used as a precipitation reaction.

Precipitation is a cost effective method, which is rather reliable and with instruments which are easily avaliable. However, proper skills are required to get accurate results and may be time consuming.

SPECTROSCOPY

Colorimetry is the spectroscopic technique used to determine the concentration of coloured compounds. Most coloured complexes of copper (II) are octahedral complexes.

Colorimetry is advantageous as it can be inexpensive once the instrument is purchased. The main disadvantage is that there can be interference form impurities and similar coloured compounds. To conduct very accurate analysis, more expensive instruments need to be purchased.