Question 1: Explain why transition metal compounds are often coloured. Include in your answer the role of d-electrons.

Answer: Transition metal compounds are coloured because d-electrons absorb specific wavelengths of light during electronic transitions, causing the compounds to exhibit characteristic colours.

Question 2: Describe the difference between the oxidation states of transition metals that lead to different colours in their compounds.

Answer: Different oxidation states alter the d-electron configuration, which affects the wavelengths of light absorbed and thus results in different colours.

Question 3: Calculate the number of d-electrons in a Fe(III) ion. (Atomic number of Fe = 26)

Answer: 5

Question 4: Identify which transition metal ion commonly forms a purple coloured compound and name the compound.

Answer: Potassium permanganate (KMnO4)

Question 5: Explain the importance of colour in transition metal compounds in industries such as dyes and pigments.

Answer: Colour in transition metal compounds is crucial for industries like dyes and pigments because it allows for the production of vibrant, stable colours used in textiles, paints, and cosmetics. The specific colours result from electronic transitions in the metal ions, which can be customised for different applications.

Question 6: A solution contains a copper(II) sulphate complex. Write the formula of the compound and state its colour.

Answer: CuSO4·5H2O, blue

Question 7: Describe a simple laboratory experiment to observe the colour of a transition metal compound.

Answer: Dissolve an appropriate transition metal salt, such as potassium permanganate, in water and observe the solution's colour against a white background. Use safety precautions such as wearing gloves and eye protection.

Question 8: Interpret the following scenario: A student observes a violet solution when a transition metal salt is dissolved in water. Which metal is likely involved? Provide reasoning.

Answer: The metal is likely manganese, forming potassium permanganate, which is violet due to electronic transitions in MnO4- ions.

Question 9: Calculate the concentration (mol/L) of a copper(II) sulphate solution if 5.0 grams are dissolved in 250 mL of water. (Molar mass of CuSO4·5H2O = 249.5 g/mol)

Answer: 0.02 mol/L

Question 10: Identify the variable and control variables in an experiment investigating the effect of pH on the colour of a transition metal complex.

Answer: Variable: pH of the solution; Control variables: concentration of metal ion, temperature, and type of ligand.

Question 11: Explain how the d-electron configuration affects the colour observed in a transition metal complex.

Answer: The d-electron configuration determines which electronic transitions are possible when light is absorbed, influencing the wavelength (colour) of light absorbed and thus the colour of the compound.

Question 12: Discuss the relevance of coloured transition metal compounds in developing new technologies like solar cells or catalysts.

Answer: Coloured transition metal compounds are vital in technologies such as solar cells, where their ability to absorb specific wavelengths enhances energy capture, and in catalysts, where their electronic structure facilitates chemical reactions, leading to more efficient and sustainable processes.