Question 1: Define a coloured compound in the context of transition metals.

Answer: A coloured compound is a chemical substance where the transition metal ion absorbs certain wavelengths of light, resulting in the compound displaying a specific colour.

Question 2: Explain the role of d-electrons in producing colour in transition metal compounds.

Answer: D-electrons in transition metals can absorb specific wavelengths of light to promote electrons between d-orbitals, causing electronic transitions that result in the compound's colour.

Question 3: Describe the mechanism by which ligands influence the colour of transition metal complexes.

Answer: Ligands affect the energy gap between d-orbitals in the metal ion, altering which wavelengths of light are absorbed, thus influencing the colour of the complex.

Question 1: Calculate the energy (in joules) of light absorbed by a transition metal complex that absorbs light with a wavelength of 580 nm. Use the formula E = hc/λ, where h = 6.626×10⁻³⁴ J·s, c = 3.00×10⁸ m/s.

Answer: E = (6.626×10⁻³⁴ J·s × 3.00×10⁸ m/s) / (580×10⁻⁹ m) ≈ 3.43×10⁻¹⁹ J

Question 2: A solution of copper(II) sulphate exhibits a blue colour. If the absorption maximum occurs at 610 nm, what is the energy of the absorbed photon? (h = 6.626×10⁻³⁴ J·s, c = 3.00×10⁸ m/s).

Answer: E = (6.626×10⁻³⁴ J·s × 3.00×10⁸ m/s) / (610×10⁻⁹ m) ≈ 3.26×10⁻¹⁹ J

Question 1: Describe a simple experiment to determine the concentration of a coloured transition metal solution using colourimetry. Include variables to control and safety precautions.

Answer: The experiment involves passing light through solutions of known and unknown concentrations and measuring absorbance with a colourimeter. Variables to control include light intensity, path length, and temperature. Safety precautions include wearing gloves and eye protection, handling chemicals with care, and disposing of waste properly.

Question 1: A series of transition metal complexes shows absorption maxima at 450 nm, 500 nm, and 550 nm. Explain how the change in ligand types could cause these differences in absorption wavelengths.

Answer: Different ligands alter the energy gap between d-orbitals in the metal ion, shifting the absorption wavelength. Ligands that cause a larger splitting result in higher energy (shorter wavelength) absorption, while weaker field ligands cause lower energy (longer wavelength) absorption.

Question 2: If a complex absorbs primarily red light, what is the colour of the compound as seen by the human eye? Justify your answer.

Answer: The compound appears green because it absorbs red light; the complementary colour of red is green.

Question 1: Explain why chromium(III) compounds are often green, and discuss how ligand substitution can alter their colour. Include in your answer the electronic transitions involved and practical implications for industry.

Answer: Chromium(III) compounds are green because they absorb light in the red and yellow regions, due to d-d electronic transitions within the crystal field. Ligand substitution can change the ligand field strength, shifting the absorption wavelength and thus the colour. This property is utilised in manufacturing pigments, dyes, and in analytical chemistry for identifying specific compounds.

Question 1: Provide an example of a coloured transition metal compound used in industry and explain its significance.

Answer: Copper sulphate is used as a fungicide and in electroplating due to its vibrant blue colour, which indicates its purity and concentration, essential for effective application.

Question 2: Discuss how the colour properties of transition metal complexes are exploited in modern technological devices such as sensors or displays.

Answer: Colours of transition metal complexes are used in sensors to detect specific chemicals through colour change, and in display technologies (like LCDs) where precise control of light absorption and emission enhances colour rendering and image quality.