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Describe two methods of recycling plastics.

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1. Physical Method
The physical method used in recycling plastics involves physically breaking down the plastics into very small pieces. The plastics are physically crushed into smaller pieces and blended to form a mixture of uniform homogenous quality. The blended mixture is melted and passed through a screen to form strands. This is known as extrusion. After cooling, the plastic strands are cut into pellets to be used as materials for new products.

2. Chemical Method
The chemical methods used in recycling plastics involve chemically breaking down the long-chain molecular structure in plastics into smaller molecules.
Cracking of plastics and depolymerisation of plastics are the two common chemical methods of recycling plastics.
i. Cracking of plastics
Cracking of plastics involves heating the plastic waste to high temperatures in the presence of a catalyst. The long-chain molecules are broken down into smaller molecules. This process transformed the plastic waste into a mixture of gases, liquids and solids. This mixture is then separated and processed to create new raw materials or fuels.
ii. Depolymerisation of plastics
This process involves breaking down the plastic polymer into its monomer units. The monomers can then be purified and used to create new plastics.

What are the advantages of biofuel compared to crude oil?

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1. Biofuel is a renewable and sustainable energy source, while crude oil is non-renewable. Food crops like palm oil or sugarcane can be replenished in a relatively short period of time. Food wastes are readily available and in abundance in big, populated cities. Biofuel made from these sources is renewable and sustainable.
In contrast, crude oil reserves are depleting fast and are projected to run out in decades.

2. Biofuel from food crops is a cleaner source of energy as the carbon dioxide released during its combustion will be offset by the carbon dioxide absorbed during photosynthesis carried out over the food crops’ lifetime.
Crude oil, when combusted, produces air pollutants like sulfur dioxide, and releases carbon dioxide which is not offset by carbon dioxide absorption during photosynthesis.

Explain why alloys have different physical properties from their constituent elements.

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When other elements are added to the pure metal, the different atomic sizes of the different elements disrupt the regular arrangement of the pure metal atoms. This irregular arrangement of the different atoms results in the alloys having different physical properties from their constituent elements. When a force is applied, the atoms in an alloy cannot slide over one another easily, causing the alloy to have lower malleability, lower ductility and higher strength as compared to pure metal.

cos 2x = sin 230

7918  admin  
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Without using a calculator, find the values of x such that cos 2x = sin 2300, where -1800 ≤ x ≤ 1800 .

Fractional Distillation of Crude Oil

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(a) Fractional distillation
(b) In the furnace at the bottom of the fractionating tower, petroleum is heated to 400 oC.
The oil vaporizes and enters the fractionating tower at the bottom.
The temperature of the fractionating tower is highest at the bottom and the temperature decreases going up the tower.
As the hot vapour rises up the column, they cool and condense into the trays at various heights depending on their boiling points.
Lighter fractions with the lowest boiling points are distilled over at the top of the fractionating column.
Heavier fractions with the highest boiling points are collected at the bottom of the fractionating column.
(c) Petroleum gas, petrol, naphtha, paraffin, diesel, lubricating oil, bitumen.
(d) (i) Cracking is the breaking of long chain alkanes into shorter chain hydrocarbons.
(d) (ii) There is lower demand for the longer chain alkanes like lubricating oil, and higher demand for shorter chain alkanes like petrol and naphtha. Cracking allows the conversion of the longer chain alkanes into shorter chain alkanes in order to meet the demand for these shorter chain alkanes.