Inorganic Chemistry: Chromium (III) Complexes

Inorganic Chemistry

Experiment 1: Chromium(III) Complexes

Aim:

The primary objective of this experiment was to investigate the various properties of chromium(III) complexes. This was done primarily using chemicals such as ammonia (NH3), hydrochloric acid (HCl), BaCl2 solution and its solubility in water. Its colour in daylight was also required as an additional property.

Introduction:

The chemistry of the element chromium has a lot of diversity. This is due to the fact that it has a wide variety of oxidation numbers. These include +6,+5,+4,+3,+2,+1,-1 and -2. The most common states in which chromium occurs is in the +6 state, which is prominent in the dichromate ion (Cr2O72-) and the +3 state which is most evident in chromium oxide (Cr2O3).

On the other hand, if they are on opposite sides of the double bond, it is a trans isomer. These configurations can be applied to the chromium complexes that will be prepared. The complexes that are prepared are potassium cis-diaquabis(oxalato)chromate(III) dihydrate and potassium tris(oxalato)dichromate(III)

After this was completed, 4 g of potassium dichromate was measured in a weighing boat and then carefully transferred to another pestle and mortar. The two pestle and mortars were taken to the fume hood and were grinded until they were both a fine powdery-like substance. The dichromate powder was transferred to the oxalic acid mortar and was mixed thoroughly. This was then placed into a large beaker (preferably >150 cm3) and was moisturised with no more than 3 or 4 drops of water. It was ensured that the hydrated powder was in the centre of the beaker. The beaker was then covered with a clock glass to minimise the escape of any condensation. In the event that the reaction does not occur, it should be gently heated on a moderately warm hot-plate. When the reaction does occur, dark coloured syrup should begin to form, with the release of