TPE Revision Chemistry notes

1 © Copyrights to Thang Pang Ern 2019 GCE ‘O’ Level Chemistry Revision Chapter 1 – Kinetic Particle Theory Gases Gases are easily compressed as the volume of gas particles is negligible compared to the volume occupied by the gas. Chapter 2 – Measurement and Experimental Techniques Apparatuses for Measurement The accuracies of apparatuses used for measurement in ascending order are beaker, graduated measuring cylinder, burette then pipette. Collection of Gases The collection of poisonous gases (e.g. chlorine) when carrying out downward delivery should be carried out in a fume cupboard. Method Suitability Examples Displacement of water  Insoluble or slightly soluble in water  Hydrogen  Carbon dioxide  Oxygen Downward delivery  Soluble in water  Denser than air  Hydrogen chloride  Chlorine Upward delivery  Soluble in water  Less dense than air  Ammonia Drying of Gases We can dry a gas by passing it through a drying agent. Using conc. sulfuric acid to dry ammonia is unsuitable as the sulfuric acid will react with the ammonia to produce ammonium sulfate. Drying agent Suitability and examples Conc. sulfuric acid  Most gases Quicklime  Ammonia Calcium chloride  Most gases

2 © Copyrights to Thang Pang Ern 2019 Chapter 3 – Separation and Purification Desert Survival Kit The desert survival kit question makes use of distillation. Chapter 6 – Ionic Bonding Ionic bonding is b etween metallic and non -metallic elements and it refers to the t ransfer of electrons from one element to another. Ionic compounds are solids at room temperature. Melting and Boiling Points Ionic compounds have high melting and boiling points. Strong electrostatic forces between the positive and negative ions which are arranged in a giant crystal lattice. It requires much energy in order to separate the ions. Electrical Conductivity Solid ionic compounds do not conduct electricity since the ions are held firmly in place, indicating the absence of free-moving ions to conduct electricity.

3 © Copyrights to Thang Pang Ern 2019 Ionic compounds only conduct electricity when dissolved in a solution or in the molten state. When an ionic compound melts or when it’s dissolved in a solution, the charged ions are free to move. When an electric current passes through, solutions of ionic compounds can be decomposed into their individual elements. Chapter 7 – Covalent and Metallic Bonding Covalent Bonding Covalent bonding is between non-metallic and non-metallic elements and it refers to the sharing of electrons between elements . Covalent compounds are u sually gaseous or liquids at room temperature. Diamond – Melting and Boiling Points Diamond has high melting and boiling points. 1 carbon atom is bonded to 4 other carbon atoms, making it having a tetrahedral structure. Much energy is required in order to separate the atoms which are connected by strong covalent bonds. Since diamond contains many covalent bonds, it has a high melting and boiling point. Diamond – Electrical Conductivity Diamond does not conduct electricity. Since all the electrons in carbon are used up in bonding, there is no presence of free-moving ions to conduct electricity. Silicon(IV) Dioxide Silicon(IV) dioxide has a structure similar to diamond. Graphite – Melting and Boiling Points Graphite has high melting and boiling points. 1 carbon atom is bonded to 3 other carbon atoms, making it having a hexagonal structure. Like diamond, graphite has strong covalent bonds connected between the atoms and since there are many bonds, much energy is required to separate the atoms. Graphite – Electrical Conductivity Graphite can conduct electricity since 1 carbon atom is bonded to 3 other carbon atoms, graphite has delocalised electrons which carry the charge s from place to place and allowing it to conduct electricity.

4 © Copyrights to Thang Pang Ern 2019 Graphite – Being Slippery Graphite contains layers of carbon atoms and these layers are held by weak intermolecular forces. The layers slide over each other very easily, making graphite slippery. Metallic Bonding Metallic bonding is between metallic and metallic elements. Metals have free-moving electrons in their outer shells which form a sea of delocalised electrons around the closely-packed positive ions. These electrons carry electric charges, which explains why metals can conduct electricity. When an electric current passes through a metal, the metal will not decompose. Metallic Bonding – Melting and Boiling Points Compounds which consist of metallic bonds have h igh melting and boiling points . There are strong electrostatic forces between the positive and negative ions holding the particles together. It requires much energy to separate the particles. When electricity is passed through a compound consisting of metallic bonds, the electrons will be disrupted and will return to their original positions. Chapter 11 – Acids and Bases Types of Oxides Most oxides can be grouped into four types: acidic oxides, basic oxides, amphoteric oxides and neutral oxides. Acidic oxides Basic oxides Amphoteric oxides Neutral oxides React with acid? No Yes Yes No React with alkali? Yes No Examples CO2, SiO2 Na2O, K2O Al2O3, PbO CO, H2O

5 © Copyrights to Thang Pang Ern 2019 When passed through powdered calcium carbonate, carbon monoxide will not be removed. However, oxides such as sulfur dioxide are removed. The reason is that calcium carbonate is basic and it reacts with acidic gases. Since carbon monoxide is a neutral gas, it will not react with calcium carbonate. Chapter 12 – Salts Preparation of Salts We can prepare salts 3 ways.  Reaction of an acid with a metal, insoluble base or carbonate  Titration  Precipitation Reaction of an acid with a metal, insoluble base or carbonate Titration Precipitation Example of salt Copper(II) sulfate Sodium chloride Barium sulfate Starting materials (i.e.) Copper(II) oxide, sulfuric acid Sodium hydroxide, hydrochloric acid Barium nitrate, sodium sulfate Steps  Filter the mixture.  Collect the filtrate.  Crystallise the filtrate.  Filter to obtain the salt crystals.  Crystallise the salt solution.  Filter to obtain the salt crystals.  Filter the mixture. Preparation of Copper(II) Sulfate Fill a beaker with dilute sulfuric acid. Stir and add excess copper(II) oxide powder until no more reaction occurs with the acid . Filter to remove the excess copper(II) oxide powder. Collect the filtrate. This is the copper(II) sulfate solution. Heat till the filtrate becomes saturated. Allow the saturated solution to cool so that the salt can crystallise. Filter to collect the crystals. Wash the crystals with a little cold water to remove any impurities. Dry the crystals between 2 sheets of filter paper. Preparation of Sodium Chloride Fill a burette with dilute hydrochloric acid. Note the initial burette reading (V1 cm3). Pipette 25.0cm3 of sodium hydroxide solution into a conical flask. Add 1 or 2 drops of methyl orange indicator to the sodium hydroxide solution. The solution turns yellow. Swirl the conical flask while adding hydrochloric acid from the burette slowly until the solution t urns orange permanently. This is the end-point. Record the final burette reading (V2 – V1 cm3).

6 © Copyrights to Thang Pang Ern 2019 To obtain a pure sample of sodium chloride, pipette 25.0cm3 of sodium hydroxide solution into a conical flask. Dispense V2 – V1 cm3 of hydrochloric acid from the burette. Do not add the indicator as it will make the salt impure. Heat the solution until it is saturated. Allow the saturated solution to cool so that the salt can crystallise. Filter to collect the crystals. Wash the crystals with a little cold water to remove any impurities. Dry the crystals between 2 sheets of filter paper. The