1)PREPARATION OF A CHROME LIQUOR

1)PREPARATION OF A CHROME LIQUOR

1.AIM

·         The aim of this process is to preparing a chrome liquor by transformation of Cr(+6) to Cr(+3).

2.THEORETICAL BASIS

·         Preparation

Anhydrous chromium(+3) chloride may be prepared by chlorination of chromium metal directly, or indirectly by chlorination of chromium(+3) oxide in the presence of carbon at 800 °C, with carbon monoxide as a side-product;

   Cr₂O₃ + 3 C + 3 Cl₂ → 2 CrCl₃ + 3 CO

It may also be prepared by treating the hexahydrate with thionyl chloride. The hydrated chlorides may be made by dissolving the metal in hydrochloric acid.

However, it is also a chloro complex which is quite inert to substitution, so in fact it is ordinarily quite unreactive. Slow reaction rates are common with chromium(+3) complexes in general. The low reactivity of the d ³ Cr³⁺ ion can be explained using crystal field theory. One way of opening CrCl₃ up to substitution in solution is to reduce even a trace amount to CrCl₂, for example using zinc in hydrochloric acid. This chromium(2) compound undergoes substitution easily, and it can exchange electrons with CrCl₃ via a chloride bridge, allowing all of the CrCl₃ to react quickly.

·         Reactions

CrCl₃ is a Lewis acid, classified as "hard" according to the Hard-Soft Acid-Base theory. It forms a variety of adducts of the type [CrCl₃L₃]^z, where L is a Lewis base. For example, it reacts with pyridine (C₅H₅N) to form an adduct:

   CrCl₃ + 3 C₅H₅N → CrCl₃(C₅H₅N)₃

Like most chromium(+3) compounds, CrCl₃ is chemically inert but its neighboring redox state chromium(2) is reactive. Thus, CrCl₃ and its complexes generally react only sluggishly in the absence of a reducing agent capable of reducing Cr³⁺ to Cr^2+. With the presence of some chromium(II), however, solid CrCl₃ dissolves rapidly in water. Similarly, ligand substitution reactions of solutions of [CrCl₂(H₂O)₄]+ are accelerated by chromium(2) catalysts.

3.MATERIAL AND PRODUCT

·         500 mL vessel, 15 mL burret.

·         Potassium dichromate, sucrose, sulfuric acid, Chromium(+6).

4.METHODOLOGY

·         We had weighed 20 g of either potassium dichromate in a precipitate vassel of 500 mL, partially they were dissolved in 40 mL of water. We had prepared 25 mL of a dissolutions of sucrose at 30%. And we had added 20 g of sulphuric acid slowly and shaked in order to complete the dissolution of dichromate. Before it cools down, we had added 20 mL of the dissolution of sucrose. We had left it to one side until the following day. We had checked the colour.The colour turned from orange(+6) to gren(+3). At final, we have obtained a chrome liquor (+3).

5.CALCULATIONS, RESULT AND ASSESMENTS

·         There are not any calculations.

6.CONCLUSIONS

·         There are not any coclusions.

7.BIBLIOGRAPHY

·         Earnshaw Alan. (1997), Chemistry of the Elements (2nd ed.)

·         D. Nicholls, Complexes and First-Row Transition Elements, 1973.

• TOPTAŞ Ahmet, Deri Teknolojisi, T.C.İstanbul Üniv. Tek. Bil.Yük.Okulu Öğr.Gör. Erdiz Masa Üstü Yayıncılık 1993-İSTANBUL