Write a balanced equation using chemical formulae for this reaction - Leaving Cert Chemistry - Question Question (f - j) - 2019

To calculate the percentage by mass of zinc in zinc oxide, we first need to find the molar mass of ZnO:

• Molar mass of Zn (Zinc) = 65 g/mol
• Molar mass of O (Oxygen) = 16 g/mol
• Molar mass of ZnO = 65 + 16 = 81 g/mol

Next, we calculate the percentage of zinc in ZnO:

$\% \text{Zn} = \left( \frac{65}{81} \right) \times 100 \approx 80.2\%$

Therefore, the percentage by mass of zinc in zinc oxide is approximately 80.2%.

The octane number of a fuel indicates its ability to resist knocking during combustion. A higher octane number means the fuel can withstand greater compression before igniting, leading to smoother engine performance and reduced knocking. Fuels with higher octane ratings are typically used in high-performance engines.

During the secondary stage of sewage treatment, biological processes are employed to degrade organic matter. This stage typically involves aeration tanks where microorganisms consume the organic pollutants, breaking them down into simpler substances. The treated sewage then undergoes sedimentation to separate the biomass from the clean water before further purification.

Temporary water hardness, which is caused by the presence of dissolved bicarbonate minerals (mainly calcium and magnesium bicarbonates), can be removed by boiling. When boiled, these bicarbonates decompose into insoluble carbonates, which precipitate out of the water, thereby softening it.