Carbon dioxide is a simple covalent compound, consisting of discrete molecules. The molecules are held together by weak intermolecular forces of attraction. Very little energy is needed to break these weak bonds, hence carbon dioxide has low melting point and boiling point.
Category: FAQs
Total Internal Reflection and the Brilliance of Diamonds
A diamond is cut in such a way that the flat shape of the crown allows for the maximum number of light rays to either reflect off the crown or refract into the diamond.
The critical angle of diamonds will be small as the refractive index of diamond is high.
The shape and angle of the pavillion is such that most light rays falling on it will have an angle of incidence greater than the critical angle. This allows for total internal reflection to occur, causing light rays to reflect multiple times within the diamond, and leave the diamond through the crown.
The multiple light rays leaving the crown of the diamond makes it look more brilliant to an observer looking at the crown of the diamond.
Describe a method of preparing silver chloride from the reaction of silver nitrate and dilute hydrochloric acid.
The silver chloride salt can be prepared using the precipitation method.
Add equal volumes of dilute hydrochloric acid to a beaker containing aqueous silver nitrate.
Stir the solution. A white precipitate of silver chloride is formed.
Filter the mixture to obtain silver chloride as the residue. Wash the residue with cold distilled water and dry between two pieces of filter paper.
Describe a method of preparing copper(II) sulfate from the reaction of copper(II) oxide and dilute sulfuric acid.
The copper(II) sulfate salt can be prepared using the filtration method.
Copper(II) oxide is added in excess to a fixed volume of dilute sulfuric acid.
Filter the mixture to remove the excess copper(II) oxide from the copper(II) sulfate solution.
The filtrate of copper(II) sulfate is then heated until saturated.
The saturated solution is allowed to cool so that crystals of copper(II) sulfate can be formed.
Filter the mixture to remove the excess water.
Wash the crystals with a little bit of cold distilled water and dry between two pieces of filter paper.
Describe how a force is exerted on a current-carrying conductor that is cutting through the magnetic field of a magnet.
When a current flows through the current-carrying conductor, a magnetic field forms around the current-carrying conductor.
The interactions between the magnetic fields of the current-carrying conductor and the magnet produce regions of unequal magnetic field densities around the conductor.
A force will be exerted on the conductor, moving it towards the region of lower magnetic field density.
Why must the fuse/switch/circuit breaker be connected to the live wire?
The live wire is at high voltage, and carries the current from the electrical mains to the electrical appliance. If any electric fault occurs, resulting in high current flow, the fuse/switch/circuit breaker on the live wire will immediately cut off the high current/high voltage before the high current/voltage can cause damage to the electrical wirings and the appliance.
Explain why calcium oxide has a higher melting point than potassium fluoride.
The charges of Ca2+ ions and O2- ions in CaO is higher than that of K+ ions and F– ions in KF. The higher the ionic charge, the higher the electrostatic force of attraction between the oppositely charged ions, so more energy is required to overcome the electrostatic force in CaO than in KF.
Hence, CaO would have a higher melting point than KF.
What is the potential hazard when the switch of an electrical appliance is connected to the neutral wire instead of the live wire?
The live wire is at high potential difference, while the neutral wire is at zero potential difference. When the switch is turned off, the electrical appliance will still be at high voltage, since the electrical appliance is still connected to the electrical mains via the live wire.
The electrical appliance being ‘live’ even though the switch is turned off is potentially hazardous as it increases the risk of electrocution and overheating and electric fire if a path to a lower potential difference is established.
Q&A Sigma Notation (#3)
List some examples of reducing agents and oxidizing agents
Reducing agents:
carbon (C)
carbon monoxide (CO)
hydrogen (H2)
hydrogen sulfide (H2S)
metals
potassium iodide (KI)
sulfur dioxide (SO2)
ammonia (NH3)
hydrogen peroxide (H2O2)
(can act as oxidizing agent as well)
Oxidizing agents:
fluorine (F2)
chlorine (Cl2)
bromine (Br2)
iodine (I2)
concentrated sulfuric acid (H2SO4)
nitric acid (HNO3)
oxygen (O2)
potassium manganate(VII) (KMnO4)
potassium dichromate(VI) (K2Cr2O7)
hydrogen peroxide (H2O2)
(can act as reducing agent as well. It is stronger as an oxidizing agent, especially in acidic solutions)