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.
Category: Pure Chemistry
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.
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.
Describe an experiment to study the speed of reaction between calcium carbonate and dilute hydrochloric acid, by measuring the loss in mass of reaction system over time.
The apparatus is set up as shown in the diagram below.
The initial mass of the reaction system is recorded.
The thread is pulled to mix the calcium carbonate and acid. The stopwatch is started at the same time.
The mass of the reaction system is recorded every one-minute.
From the data collected, a graph of mass of reaction system against time taken is plotted.
From the slope of the graph, the speed of reaction can be studied.
The steeper the gradient of the graph, the faster the speed of reaction.
Describe an experiment to study the speed of reaction between dilute hydrochloric acid and magnesium, by measuring the volume of gas produced over time.
The apparatus is set up as shown in the diagram below.
The thread is pulled to mix the magnesium ribbon and acid. The stopwatch is started at the same time.
The volume of hydrogen collected in the gas syringe is recorded every half-minute.
From the data collected, a graph of volume of gas produced against time taken is plotted.
From the slope of the graph, the speed of reaction can be studied.
The steeper the gradient of the graph, the faster the speed of reaction.
Explain, using structure and bonding, why copper(II) nitrate cannot conduct electricity when solid, but can conduct electricity when molten or aqueous.
Copper (II) nitrate is an ionic compound. In the solid state, the ions of copper (II) nitrate are held in fixed positions in a giant ionic lattice structure. There are no mobile ions to conduct electricity.
In the molten or aqueous state, the giant ionic lattice structure is broken down. The ions are now able to move about. These mobile ions can act as charge carriers.