AL-Hussein Bin Talal University Science college Chemistry Department Inorganic Chemistry Laboratory Number of experiment 2 Preparation of potassium cis-and transDioxalatodiaquochromate
Introduction In this experiment we want Preparation of potassium cis-and trans-Dioxalatodiaquochromate(III) ,the metal we use it potassium dichromate, Chromium (symbol Cr and atomic number 24) occurs in the oxidation states 0, +2, +3, and +6 states. Element (0) and divalent chromium, however, are unstable ,the coordination number of it Chromium (III)have coordination number 6 (octahedral coordination and in this experiment we want use Cr(III) have coordination number 6 ,and also Cr(III)have coordination number 4 (tetrahedral complex). The physical and chemical property :- is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is potentially harmful to health and must be handled and disposed of appropriately. It is a crystalline ionic solid with a very bright, red-orange color ,and potassium dichromate it has a melting point(398C),boiling point (500C(decompose)),specific gravity equal (2.676),and it is soluble in water ,but insoluble in alcohol , and it is stable under ordinary condition. ,the ligand we use in this experiment it water (H2O) and Oxalic acid (Oxalic acid dehydrate),the form for it
The physical and chemical property :Oxalic Acid (also called Ethanedioic Acid) is a colorless, crystalline, toxic organic compound belonging to the family of dicarboxylic acids; melting at 187 C; soluble in water, alcohol, and ether. It occurs in the form of its metal salts (usually calcium or potassium) in many plants. It is commercially manufactured by heating sodium formate in the presence of an alkali catalyst to form sodium oxalate, which should be converted to free oxalic acid when treated with sulfuric acid. Oxalic acid is the only possible compound in which two carboxyl groups are joined directly; for this reason oxalic acid is one of the strongest acids in organic compounds. Unlike other carboxylic acids, oxalic acid (and formic acid) is readily oxidized and combine with calcium, iron, sodium, magnesium, or potassium to form less soluble salts called oxalates. Oxalic acid and oxalates are useful as reducing agents for photography, bleaching, and rust removal. They are widely used as an purifying agent in pharmaceutical industry, precipitating agent in rare-earth metal processing, bleaching agent in textile and wood industry, rust-remover for metal treatment, grinding agent, waste water treatment. acid rinse in laundries and removing scale from automobile radiators. Oxalic acid dehydrate ,has a white crystals as a physical state , the melting point for it between (101-102C),the boiling point for it (149-160C),the specific gravity is between (1.6-1.7),it is soluble in water and it is stable under ordinary condition .coordination bond for it; oxalate ion (ox) Oxalate ion is a bidentate ligand even though it contains four O atoms which have lone pairs of electrons , it is Bidentate ligand is Lewis bases that donate two pairs ("bi") of electrons to a metal atom. Bidentate ligands are often referred to as chelating ligands because they can "grab" a metal atom in two places. The complexes we preparation it :- the reaction for cis and trans is :K2Cr2O7 + 7H2C2O4 →6CO2 + 13H2O +2K Cr(C2O4)2.2H2O For Cis isomer:- The Physical and chemical property :-in spectrophotometer methods since in solution the cis isomer absorb much more strongly ,that by the color of it ,it has high dark color ,so give much peak ,much intensity ,and it is polar ,and the product for it . Cis is kinetic because it produces high temperature .solid state and kinetic and polar,the color of complex black. Fast reaction
For trans isomer :- the trans is thermodynamic need to temperature to the reaction happened . Solid state and dark blue . Thermodynamic and nonpolar ,the color of complex dark blue Slow reaction.
Calculation :Theoretical yield K2Cr2O7 + 7H2C2O4 →6CO2+13H2O+2KCr(C2O4)2.2H2O I mol of K2Cr2O7 = 2 mol of KCr(C2O4)2 4 g/294.1886 g/mol = 0.01359671993 mol of K2Cr2O7 Mol of KCr(C2O4)2.2H2O = 2* mole of K2Cr2O7 Mol of *M.W Mass of KCr(C2O4)2.2H2O = =7.752694699 g Percentage Yield of complex: % yield for Cis = (Actual mass/ Theoretical.)*100% = (4.376/7.752694699)*100% = 56.44% % yield for trans = (0.744 g/7.752694699g)*100% = 9.5966 % Discussion :Chromium Oxalate:Chromium Oxalate is produced by the reaction of oxalic acid with a chromium salt. Chromium Oxalate is a highly specialized product finding use in metal treatment and plating and the pharmaceutical industry. A- For cis-Dioxalatodiaquochromate :1- In this experiment firstly we use powder oxalic acid(Oxalic acid dihydrate) ,C2O4H2, C2O2(OH)2.
2- Oxalic acid is the chemical compound, colorless solid is a dicarboxylic acid, Its conjugate base, known as oxalate (C2O42-), is a reducing agent. 3-In this experiment we use it as ligand, exactly a chelating agent for metal cations. 4-We were crushed the powder oxalic acid(Oxalic acid dihydrate) that well, to obtain very small particle. 5- After that we get dichromate, Potassium dichromate. 6- Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications, It is a crystalline ionic solid with a very bright, red-orange color. 7- We were crushed Potassium dichromate that well, to obtain very small particle. 8-After that mix them as intimately as possible by grinding them gently together, to product approximately Yellowish orange powder .
9- After that we put the Yellowish orange powder(the mixture ),on the basin and cover it ,after that warm very gently ;because the mixture empowering suddenly; soon a vigorous reaction sets in ,with evolution of steam and CO2. This operation :K2Cr2O7 + 7H2C2O4→ 6CO2 + 13H2O + 2K Cr(C2O4)2.2H2O K2Cr2O7, happened for it reduction to product Cr+3,and also evolution of steam and CO2.,by reducing agent, it is Oxalic acid (ligand). 10-After that we were poured ethanol over the product we were obtain, For cleaning, so as not to turn into trans. 11-we were put ethanol and stir until the product, is entirely crystalline and granular (the product ,purple-black). B- For trans-Dioxalatodiaquochromate :1- In this experiment firstly we use powder oxalic acid(Oxalic acid dihydrate) ,C2O4H2, C2O2(OH)2.
2- Oxalic acid is the chemical compound, colorless solid is a dicarboxylic acid, Its conjugate base, known as oxalate (C2O42-), is a reducing agent. 3-In this experiment we use it as ligand, exactly a chelating agent for metal cations. 4-Firstly we were prepare two separately solutions, oxalic acid solution and dichromate solution, by using boiling water. 5- Boiling water to speed up the interactions for the solutions, and we were use water to product trans isomer . 6-Also we note, when we were do this experiment, after we were add the dichromate solution above oxalic acid solution we cover the solutions, to reaction proceeds. 7-But this reaction took For a long time, as the solution did not settle quickly(trans did not settle quickly);because the trans isomer has high dissolvent ,so did not sediment quickly. 8-finally we obtain rose-colored crystals of the trans isomer. Structure complex:Chromium : atomic number 24, wt 52, configuration [Ar]3d54s1 . Common states Cr+3 and Cr+6( ie. CrO4-2). Chromium tanning is between collagen and Cr+3. 6 coordination positions(octahedron) are present, and stereoisomer are possible
1-isomers :cis and trans an octahedral complex, geometrical isomers Cis:- cis bis chelate Trans:-trans bis chelate
it has the d3 configuration and it is optically active ,which do not have improper relation axis.
:II-Shape
-:III-distortion Octahedral complexes of d9 and high -spin d4 ions are often + distorted example for that CuF2 and [Cr(OH2)6]2 so that two metal-ligand bonds(axial) are different lengths from , the remaining four (equatorial);SO 2K Cr(C2O4)2.2H2O ,cis and trans, an octahedral complex, it . has the d3 configuration so no distortion -: Bonding : electron configuration -1 For Cr: [Ar] 3d5 4s1 And the electronic configuration of complex (cis and transe)is t2g3 eg0 :Point group (2 . Trans:- trans bis chelate;optically in active D2h .Cis :- cis bis chelate;optically active C2v -:splitting and crystal field theory (3 In this experiment we use two ligands ,are Oxalate(OX) and water(H2O) as ligand which they effect in the splitting
I-
4-electron transition:4
A2→4T2(G) and 4A2→4T1(F) transitions.
Questions : Q1:
Q2: in Cis isomer where it polar the high intensity and the high, molar peak. Q3:we can diferretiant between cis & trans through the color , Cis black ;trans dark blue
