Question 1: Define a coloured compound of a transition metal and explain why these compounds are often colourful.

Answer: A coloured compound of a transition metal is a chemical that contains a transition metal ion and exhibits colour due to d-d electron transitions or charge transfer. The colour arises because specific wavelengths of light are absorbed, exciting electrons between different d orbitals.

Question 2: Describe the role of ligand field theory in explaining the colour of transition metal complexes.

Answer: Ligand field theory explains that ligands create an electric field around the metal ion, splitting the degenerate d orbitals into different energy levels. The absorption of specific light wavelengths corresponds to the energy difference between these levels, producing colour.

Question 3: What is the typical oxidation state of chromium in the coloured compound potassium dichromate (K₂Cr₂O₇)?

Answer: Hexavalent (+6)

Question 1: Calculate the concentration in mol/dm³ of a potassium dichromate solution if 25.0 cm³ of it reacts with 40.0 cm³ of 0.1 mol/dm³ sodium thiosulphate (Na₂S₂O₃) in a redox titration. (Use the equation: Cr₂O₇²⁻ + 3 S₂O₃²⁻ → 2 Cr³⁺ + 3 S₄O₆²⁻)

Answer: Concentration of K₂Cr₂O₇ = 0.03 mol/dm³

Question 1: Describe a safe method to prepare a dilute solution of copper sulphate (CuSO₄) in the laboratory. Include safety precautions.

Answer: To prepare a dilute copper sulphate solution, carefully add a small amount of copper sulphate crystals to distilled water while stirring. Wear safety goggles and gloves to prevent skin and eye contact. Use a fume hood if necessary. Ensure the solution is fully dissolved before use, and label the container clearly.

Question 2: Identify the independent and dependent variables in an experiment where you observe the colour change of a transition metal complex as pH varies.

Answer: Independent variable: pH of the solution. Dependent variable: Colour of the transition metal complex.

Question 1: A solution containing a transition metal complex appears deep blue. The solution's absorption spectrum shows a peak at approximately 600 nm. Explain the reason for this colour based on electronic transitions.

Answer: The deep blue colour is due to the complex absorbing light around 600 nm, which corresponds to the energy required for d-d electron transitions within the metal ion's d orbitals. The absorption of light at this wavelength results in the complementary colour, blue, being observed.

Question 1: Explain how ligand type influences the colour of a transition metal complex. Include an example in your answer.

Answer: The ligand type affects the ligand field strength, which influences the splitting of d orbitals in the metal ion. Strong field ligands, such as CN⁻, cause larger splitting, resulting in absorption of different wavelengths and thus different colours. For example, [Co(NH₃)₆]²⁺ is pale yellow due to ammonia ligands, whereas [Co(CN)₆]⁴⁻ is deep blue because cyanide is a stronger field ligand.

Question 1: Describe at least two applications of coloured transition metal compounds in industry or technology, explaining the scientific principle behind each.

Answer: Coloured transition metal compounds are used in dyes and pigments, such as chromium oxide in green pigments, because their ability to absorb specific wavelengths of light gives them their colour. They are also used in photographic processes, where their light absorption properties help develop images with specific hues.