Embed Size (px)
Citation preview
Created by Shahzad Raza
Gcse – Chemistry Revision Notes
Reactivity Series• The following list shows how reactive different elements are in relation to each other.
This is a shortened list but contains most of the elements that you need to know about. Potassium (Very reactive)SodiumCalciumMagnesiumAluminiumCarbonZincIronTinLeadHydrogenCopperSilverGold (Very unreactive)
Periodic Table
• (Elements highlighted in a red font are important elements which you should really know about)
Important Ions
• The table below lists some important ions that you should really know about:
• Name of Ion Formula• Hydroxide OH (-) • Carbonate CO3 (-2)
• Sulphate SO4 (-2)
• Nitrate NO3 (-)
• Ammonium NH4 (+)
Bonding• This occurs in metals and is when electrons are given out from the metal atoms to make a "sea"
of free electrons in between all of the metal atoms. These free electrons hold the metal as a mass together. This is known as being a giant structure.
• The free electrons present make it possible for electricity to be transferred easily because the charge is carried by them. Because the metal atoms have lost electrons, they have a positive charge.
Ionic Bonding This occurs typically between a metal and a non-metal (from groups 1 + 2 and 6 + 7 on the periodic table). The metal atom loses electrons which are taken by the non-metal. Therefore, the metal ion produced has a positive charge and the non-metal ion is negatively charged. Sodium (metal - group 1) + Chlorine (non-metal - group 7) ----> Sodium Chloride (NaCl) In the example above, the sodium atom has lost an electron to form a positive ion. The chlorine atom has gained the electron lost from the sodium to form a negative ion. The NaCl molecules are arranged in a giant structure to form the substance more commonly known as Salt.
Covalent Bonding This is when electrons are shared between atoms. Covalent bonding occurs between non-metals due to the fact that all of the atoms need to gain electrons, so they have to share. Common substances that covalent bonding occurs in: Water (H2O), Hydrogen gas (H2), and Methane (CH4)
Ion Analysis• Testing for Cations Cations are positively charged (+) ions. There are 2 basic tests for them: • Flame test • Adding NaOH (aq) to solution of ionic compound
• The flame test involves a clean nichrome wire first being dipped into a solution of Hydrochloric acid. This is then dipped into the solid powdered compound of the metal being tested. This is then held over a Bunsen Burner and the flame colour is observed. T
• he following results are gained for each ion: • Na+ - Yellow flame • K+ - Lilac (light purple) flame • Ca2+ - Red flame • Cu2+ - Blue / green flame
• The second test of adding NaOH (sodium hydroxide) gives a coloured precipitate. The colour of this precipitate reveals which ion is present. The following results are gained for each ion:
• Ca2+ White precipitate - Ca(OH)2 (s)
• Cu2+ Blue precipitate - Cu(OH)2 (s)
• Fe2+ Green precipitate - Fe(OH)2 (s)
• Fe3+ Brown precipitate - Fe(OH)3 (s)
• To detect the Hydrogen ion (H+), which is not a metal, but still has a positive charge, Universal indicator can be used, which will turn red. (because anything with the hydrogen ion in it is an acid)
Electrolysis• This is the (chemical) process by which a compound in its molten state is decomposed to form its elements.
Some of its uses are as follows: Extraction of reactive metals from their ore. (e.g. - aluminium from bauxite) • Electroplating • Chloralkali Industry - electrolysis of brine to produce chlorine, hydrogen, and the alkali, sodium hydroxide. • Purification of metals (e.g. - copper) • Anodising • Metals Metals conduct electricity in their solid state or when they are melted but they are NOT decomposed in the
process (i.e. a chemical reaction does not occur). Metals can conduct electricity because in their structure, each metal atom gives up its outer shell electrons to form a sea of delocalised electrons. This means that the electrons are free to move through the metal's structure and therefore conduct electricity.
• Electrolytes • Non-metals, apart from graphite, do not possess freely moving electrons and so, they are insulators. • A compound that is in its molten or aqueous state conducts electricity and is decomposed by it. The current is
carried by ions which are free to move through the liquid to the oppositely charged electrodes where they are discharged (acids / alkalis / salts are all examples). Ions are not mobile when a compound like this is in its solid state.
• Electrodes • Cathode (-) electrode - Positive ions are attracted to it. Positive ions are called Cations (e.g. Na+) • Anode (+) electrode - Negative ions are attracted to it. Negative ions are called Anions (e.g. Cl -) • An Example of Electrolysis • Lead Bromide (PbBr2) can undergo electrolysis to form bromine gas and lead. The lead bromide is melted in a
heat resistant vessel. The electrodes are put into the liquid and they are connected to an electrical circuit. • After a short time, a layer of metal (lead) is deposited around the cathode (negative). Also, clouds of orange gas
(bromine) form around the anode (positive). • The following equations show the reactions taking place: • (At the cathode) Pb2+ + 2e- ----> Pb (neutral atom) • (At the anode) 2Br - - 2e- ----> Br2 (bromine molecule)
Chemical Changes• Thermal Decomposition
A single substance is broken down by heating. A good example of this is the cracking of hydrocarbons. DisplacementWhen one more reactive element pushes another less reactive element out of a compound. This mainly occurs with metals.
• e.g. Magnesium + Iron Sulphate ----> Magnesium Sulphate + Iron • Neutralisation
An acid and an alkali react to form a neutral product • Precipitation
A solid (the precipitate) is formed from the reaction of two solutions (i.e. no solids present at beginning of reaction) • Exothermic Reactions
A reaction that GIVES OUT heat. (e.g. combustion of fuels) • Endothermic Reactions
A reaction that TAKES IN heat. This energy is used to form the bonds needed to gain the products. • Reduction
The GAIN of electrons. This is the opposite to oxidation. • e.g. Iron oxide ----> Iron • Oxidation
The LOSS of electrons. This is the opposite to reduction. • e.g. Iron + Oxygen ----> Iron Oxide
Hard Water• Hard water does not produce as much lather as soft water when it is used
with soap and also an insoluble solid called scum is left on the sides of the wash basin. Calcium chloride, Magnesium nitrate, and Iron (II) Sulphate produce scum and no lather when contained in a sample of water that is mixed with soap.
• The ions that are responsible for "Hard Water" are therefore as follows: • Ca2+ • Mg2+ • Fe2+ • Hard water is formed by 2 main methods: H2O (l) [In rain] + CO2 (g) [In
air] ----> H2CO3 (aq) [Carbonic Acid] This carbonic acid flows over chalk / limestone - reacts with calcium to form Calcium Hydrogen-carbonate. This is now soluble in water and so can cause hard water
• CaCO3 (s) + H2CO3 (aq) ----> Ca(HCO3)2 (aq) [Calcium Hydrogen-carbonate]
Scum Formation
• Soap contains salts such as sodium stearate and sodium palmitate and when calcium ions in hard water mix with soap, a precipitate of calcium stearate / calcium palmitate is formed. In the following equation, "X" represents either the stearate/palmitate:
• Ca2+ (aq) + 2X- (aq) ----> CaX2 (s)Calcium (in hard water) + Palmitate/stearate ions in soap ----> Scum
• Some advantages of hard water as follows: Taste supposedly better • Strengthens bones/teeth • With correct diet, it can reduce the risk of heart disease • Some disadvantages of hard water: Needs more soap to form a
lather • Scum formed in wash basins etc... • Scale will build up in pipes and reduce the efficiency of machinery
using those pipes
Water Softening• Temporary Hard Water This is caused by calcium or magnesium hydrogen-carbonate. It can be
removed by boiling the water. • Ca(HCO3)2 (aqueous) ----> CaCO3 (solid) + H2O (liquid) + CO2 (gas)
• This above reaction is the direct opposite of when hard water forms. Boiling water is only an effective method of softening small volumes of water. It is time consuming and expensive for large quantities. Permanent Hard Water
• This is caused by calcium sulphate and CANNOT be reversed by boiling the water. There are two main methods that can be used in this situation.
• Using Na2CO3 (washing soda) - this can remove both types of hard water...
• Hard Water + Washing Soda ----> Scale + Softened Water • CaSO4 (aq) + Na2CO3 (s) ----> CaCO3 (s) + Na2SO4 (aq)
Ca(HCO3)2 (aq) + Na2CO3 (s) ----> CaCO3 (s) + 2NaHCO3 (aq)
• Using an Ion Exchange Column • Ca2+ (aq) + 2Na+ (s) ----> Ca2+ (s) + 2Na+ (aq) • Hard Water passes through a column containing a suitable resin in small granules. The column
contains an excess of sodium ions. When the hard water passes through the column, the Ca2+ ions in the water are exchanged for Na+ ions.
• The Na+ ions on the column are recharged at intervals by passing a concentrated solution of sodium chloride through the column. Na+ ions do not cause hardness and so the water is soft. Domestic water softeners work on this principal.
Water Purification• GCSE Chemistry > Water Purification
There are 3 main processes undertaken in the water purifying process: Filtration
• Bacterial Oxidation • Chlorine Treatment • The different stages are listed in more detail below: Water pumped from
river into a reservoir • Water fed into sedimentation tank where solids settle • Sand beds filter out smaller particles • Chlorine added to water to kill germs • Sulphur Dioxide then removes the chlorine • Possibly, water is filtered through GAC (Granular Activated Carbon). This
improves the taste and smell of the water • Possibly, fluorides added to water • Water is then pumped to its users
Carbon Cycle• The carbon cycle is simply the process by which Carbon Dioxide is put into and removed from the atmosphere.
This process is very finely balanced to keep the percentage of CO2 in the atmosphere at 0.03%. Even so, man is doing his part to unbalance this cycle by excess burning of fossil fuels and deforestation. The reactions involved in the carbon cycle are as follows:
• Combustion - exothermic reactions at a very fast rate Fuel [Methane] + Oxygen ----> Carbon Dioxide + Water (+ energy)CH4 (g) + 2O2 (g) ----> CO2 (g) + 2H2O (l)
• Evaporation of Sea Water (containing dissolved CO2) Carbon Dioxide dissolves in sea water. Some of the water evaporates and CO2 is released. This is a reversible reaction:
• Sea Water + Sunlight <----> Water + Carbon DioxideH2O (l) + CO2 (g) <----> H2CO3 (aq) [Carbonic Acid]
• Decay of Organic Matter Plants and animals decay to leave behind coal, oil, and gas after millions of years of being squashed by materials above. Some materials just decay and a form of respiration occurs that releases Carbon Dioxide. CO2 is also given off when the raw materials mentioned above decay.
• Photosynthesis Plants make sugar from light using carbon dioxide and water. These constituents are catalysed by chlorophyll in green leaves to form glucose, which the plant requires. The bi-product is Oxygen.
• Respiration Respiration is the name of the process which involves animals ingesting food and inhaling air. The inhaled air dissolves in the blood and is transported around the body. Some of the oxygen is used within cells to oxidise sugars. When this occurs, CO2, H2O, and O2 are released.
• Glucose + Oxygen ----> Carbon Dioxide + Water + Energy • Sedimentation Under extreme pressure, dead sea creatures decay without air deep underground. Over millions
of years, the sea creatures become oil, or natural gas. Also, when shells of sea creatures etc... build up in layers over millions of years, sedimentary rock can be formed.
Haber Process• The Haber process is the process by which Ammonia is
produced. Simply put, it involves combining Nitrogen and Hydrogen together as the second equation below shows. This is a reversible reaction. The nitrogen needed for the reaction comes from the fractional distillation of liquid air. The hydrogen comes from natural gas (methane - CH4). This is reacted with steam to produce hydrogen and carbon monoxide, as shown in the first equation below. The carbon monoxide is removed after this, to leave the needed hydrogen.
• Ammonia has many uses: • Making carpets • Modern fabrics for clothes • Ammonia fertilizers • NH4NO3 (ammonium nitrate) is also used as a fertilizer
in the form of granules • The reactions involved are as follows. The second
equation is a reversible reaction: CH4 (g) + H2O (l) ----> CO (g) + 3H2 (g) N2 (g) + 3H2 (g) <----> 2NH3 (g) [Ammonia]
Contact Process• The contact process is the name given to the
process by which sulphuric acid is produced. Sulphuric acid has many uses such as the manufacturing of: Paints / Pigments
• Soaps / Detergents • Fibres • Plastics • Fertilisers • The following reactions are involved: S (s) + O2
(g) ----> SO2 (g) (sulphur dioxide) 2SO2 (g) + O2 (g) ----> 2SO3 (g) (sulphur trioxide)
Organic Chemicals• Organic chemistry is the study of carbon compounds. The number of different organic
compounds which are known is well over 1 million and these compounds vary in properties, economic importance and uses (e.g. dyes, plastics, man made fibres, fuels, drugs etc...) The main sources of organic chemicals are:
• Natural Gas • Crude Oil • Coal • Wood / Plants / Animals (Biomass) • Crude oil is one of the most important sources. It is a complicated mixture of different
hydrocarbons which can be separated by fractional distillation. Hydrocarbons are compounds which contain carbon and hydrogen compounds only.
AlkanesThe general formula for alkanes is as follows: CnH2n+2 (where "n" is a constant)
The first ten members of the homologous series of the alkanes are:
CH4 (Methane)
C2H6 (Ethane)
C3H8 (Propane)
C4H10 (Butane)
C5H12 (Pentane)
C6H14 (Hexane)
C7H16 (Heptane)
C8H18 (Octane)
C9H20 (Nonane)
C10H22 (Decane)
Alkanes consist of strong covalent bonds therefore they are, on the whole, quite un-reactive. They do not react with acids, alkalis, and oxidising agents. Their most important reaction is that of combustion. The main chemical reactions that alkanes undergo are: •Combustion •Substitution with halogens •Catalytic Cracking (Methane) (Ethane)
AlkenesThe general formula for alkenes is as follows: CnH2n (where "n" is a constant) Alkenes are unsaturated hydrocarbons because they contain a double bond between two of their carbon atoms. The simplest alkene is ethene (C2H4) because "methene" (CH2) cannot exist. The first four members of the homologous series of the alkenes are: C2H4 (Ethene - Gas at room temperature/pressure)C3H6 (Propene - Gas at room temperature/pressure)C4H8 (Butene - Gas at room temperature/pressure)C5H10 (Pentene - Liquid at room temperature/pressure)
Ethene Propene
Fractional Distillation
Alcohol
Useful Revision Links
Guidelines and Assessment Material (Edexcel)http://www.edexcel.com/quals/Pages/default.aspx?id=50250
Guidelines and Assessment Material (AQA)http://www.aqa.org.uk/qual/gcse.html
Chemistry Revision Siteshttp://www.revisionlink.co.uk/chemistry/index.html
GCSE Chemistry Revision Guideshttp://www.examshop.co.uk/ks4/chemistry/index.htm
Keeping Calm For Your Examshttp://www.revisioncentre.co.uk/advice/keeping_calm.html
Created by Shahzad Raza
