First three terms of a GP
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Explain how crude oil is separated in a fractionating tower.
In the furnace at the bottom of the fractionating tower, petroleum is heated to 400 deg C.
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.
Parametric equations curve C
Explain why, going down Group I, the reactivity of the element increases.
Going down Group I, the number of electronic shells of the atom increases, and atomic radius increases. As the distance between the valence electrons and the nucleus increases, the electrostatic force of attraction between the positive protons in the nucleus and the negative valence electrons decreases.
Hence, going down Group I, the atom loses its valence electrons more readily and becomes more reactive.
vector equation of a reflected line
Heat Sinks
a(i) Copper (or any metal).
Copper, being a metal, is a good conductor of heat. The heat generated by the electronic component will be conducted away at a faster rate by the heat sink, preventing the component from overheating.
ii) Black color.
Black colored surfaces are better emitter of radiant heat than bright colored surfaces. This will help the heat sink to emit its heat to the surroundings at a faster rate, so that the heat sink do not get too hot, and will still be able to gain heat from the electronic component effectively.
b)(i) 1W –> increase by 2 deg C
so 10W –> increase by 20 deg C
Answer: 20 deg C
b)(ii) As the temperature of the heat sink increase, the rate of heat conduction from electronic component will slow down, and the rate of heat radiated to surroundings will increase. Eventually, the rate of heat conducted into the heat sink will be equal to the rate of heat emitted from it. At this point, its temperature will remain constant.
Some ice cubes are added to a glass of water at room temperature. Describe in terms of density changes, how convection currents occur in the water to cause the water to cool down faster.
The water surrounding the ice cubes near the surface of the water lose heat to the ice cubes, contract and become denser.
The denser, cooler water then sinks downwards, causing the warmer, less dense water to rise upwards to take its place. This process repeats, setting up convection currents in the water, cooling down the water faster.
Describe a method of preparing sodium chloride from the reaction of sodium hydroxide and hydrochloric acid.
The sodium chloride salt can be prepared using the titration method.
First, use a pipette to draw an accurate fixed volume of hydrochloric acid to a conical flask.
Add 2 to 3 drops of phenolphthalein into the flask.
Titrate, drop by drop, the sodium hydroxide from the burette into the hydrochloric acid. Swirl the solution each time sodium hydroxide is added to it.
When the first appearance of pink color is observed in the solution, stop the titration and note the volume of sodium hydroxide used.
Mix the exact volume of hydrochloric acid and the required volume of sodium hydroxide, without adding the indicator, to obtain the sodium chloride salt solution.
The salt solution is then heated until saturated.
The saturated solution is allowed to cool so that crystals of sodium chloride can be formed.
Filter the mixture to remove excess water.
Wash the crystals with a little bit of cold distilled water and dry the crystals between two pieces of filter paper.
How does a fuse work?
When current that is higher than the fuse rating flows through the circuit, the wire in the fuse melts and breaks the circuit.
This will prevent the high current from flowing through the wirings and the electrical appliance, preventing overheating of the wires, and damage to the appliance.
