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Question 37 — The Chemistry of Art (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1 - HSC - SSCE Chemistry - Question 37 - 2012 - Paper 1
Question 37
Question 37 — The Chemistry of Art (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1. (a) The formulae of three coordination complexes are shown. [Mn(... show full transcript
Worked Solution & Example Answer:Question 37 — The Chemistry of Art (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1 - HSC - SSCE Chemistry - Question 37 - 2012 - Paper 1
Step 1
What is the oxidation state of manganese in [Mn(NH₃)₂(H₂O)₂]²⁺?
Answer
To determine the oxidation state of manganese in the complex ion [Mn(NH₃)₂(H₂O)₂]²⁺, we first note that both NH₃ and H₂O are neutral ligands. Therefore, the total charge of the complex comes solely from the manganese ion. Let the oxidation state of manganese be denoted as x. Since the overall charge of the complex is +2, the equation can be set up as:
From this we find that:
Thus, the oxidation state of manganese in this coordination complex is +2.
Step 2
Draw a Lewis structure of ONE of these coordination complexes, and describe the bonding in this molecule.
Answer
We will consider the complex [Mn(H₂O)₆]²⁺ for this part.
Lewis Structure: In the Lewis structure of [Mn(H₂O)₆]²⁺, the manganese ion is surrounded by six water molecules. Each water molecule acts as a ligand, providing a lone pair of electrons to form coordinate covalent bonds with the manganese. This can be represented as:
H H
\ /
O
/ \
Each H₂O molecule connects to the Mn ion at its oxygen, forming six coordinate bonds.
Bonding Description: The bonding in this molecule involves coordinate covalent bonds where the lone pairs of the oxygen atoms in water ligands are donated to the manganese ion. This stabilizes the complex and allows manganese to attain a stable electronic configuration, involving d-orbital participation in bonding.
Step 3
Why has copper sulfate pentahydrate (CuSO₄·5H₂O), with its strong blue colour, not been used as a pigment?
Answer
Copper sulfate pentahydrate, despite its vibrant blue color, has not been used as a pigment primarily due to its toxicity. When used in paints, it can leach out and contaminate surfaces, posing environmental and health risks. Additionally, it has been found to be a harmful substance when ingested or inhaled, thus restricting its application in consumer products such as paints and coatings. Furthermore, the stability of copper sulfate in various conditions can vary, leading to potential degradation over time, resulting in an unreliable pigment.
Step 4
Describe a named process that can be used to attach pigments to surfaces.
Answer
A commonly used process for attaching pigments to surfaces is known as 'adsorption'. In this process, pigments are typically mixed with a binder to enhance adherence to the substrate. The binder can be a polymer or a resin that coats the pigment particles, allowing them to adhere better to surfaces through physical and chemical interactions. After applying the mixture, the solvent evaporates, leaving the pigments strongly attached to the surface, creating a durable and vibrant finish.