The electron configuration of an atom may be represented by using arrows to indicate electrons and boxes to indicate orbitals - HSC - SSCE Chemistry - Question 34 - 2018 - Paper 1

In general, electrons fill sub-shells based on energy levels rather than simply by shell number. The order of filling is determined by the Aufbau principle, which states that electrons occupy the lowest energy orbitals first.

For instance, the 4s sub-shell has a lower energy level compared to the 3d sub-shell, hence the 4s will be filled before the 3d. The typical order of filling is: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p.

Thus, before the 3rd shell is entirely filled, electrons will occupy the 4s sub-shell.

To determine the oxidising strength of potassium permanganate:

1. Set up a galvanic cell using potassium permanganate as one of the electrolytes.
2. Use a reference electrode, such as a standard hydrogen electrode, versus which to measure the potential.
3. Add a reducing agent (like bromide ions) to the solution.
4. Measure the change in color as the potassium permanganate reacts.
5. Record the potential change and observe the color changes as the reduction occurs.

Upon conducting the experiment, the observation is that potassium permanganate (KMnO₄) decolorises as it reacts with bromide ions. The half-equations can be represented as follows:

ext{Oxidation: } 	ext{Br}^- 

ightarrow ext{Br}_2 + 2e^-

ext{Reduction: } 	ext{MnO}_4^− + 8H^+ + 5e^- 

ightarrow ext{Mn}^{2+} + 4H_2O

The conclusion is that potassium permanganate is a strong oxidising agent as it effectively reduces bromide ions in the solution, resulting in color change from purple (KMnO₄) to colorless (Mn²⁺). This indicates its role in the oxidation of bromide ions.

An absorption spectrum represents the range of wavelengths absorbed by a substance when it absorbs light, appearing as dark lines or bands on a continuous spectrum. It indicates the energies of electrons transitioning from lower to higher energy states.

In contrast, an emission spectrum shows the wavelengths of light emitted by a substance when its electrons drop from higher to lower energy levels, producing distinct colored lines on a black background. Each element has a unique emission spectrum.

Infrared (IR) and ultraviolet (UV) light are used to identify chemical compounds by analyzing their interaction with light. IR light causes molecular vibrations, helping identify functional groups present in pigments, whereas UV light is effective for electronic transitions.

In determining concentration, both methods enable comparison against standard samples. For example, the intensity of absorbance at specific wavelengths correlates to concentration as dictated by Beer-Lambert Law, allowing quantification of pigment concentrations in a sample.

Aboriginal cultures traditionally used ochres, derived from naturally occurring hydrated oxides, for body paint and art. Common pigments included yellow ochre (iron oxide, Fe₂O₃·nH₂O) and red ochre (Fe₃O₄). These pigments were ground into powder, mixed with a binding agent (like water or animal fat) to create a paste, and applied to surfaces such as rock or skin.

Ancient Egyptians utilized similar techniques, preparing pigments from various minerals, such as Egyptian blue (CuSiO₃·nCu(OH)₂) or azurite (Cu₂(CO₃)(OH)₂). These pigments were mixed with binders like gum arabic for cosmetic and decorative purposes, applied to walls, artifacts, or body.

Overall, both cultures demonstrated extensive knowledge in sourcing and using natural materials for art.