General
… Type of reactions include:
Neutralisation (reacting an acid with an alkali to produce a neutral pH7 solution)
Combustion (reaction with oxygen, O2)
Displacement (where a more reactive element ‘kicks out’ a less reactive element from a compound)
Precipitation (producing a solid from two reacting solutions)
Hydration (adding water)
Hydrogenation (adding hydrogen)
Decomposition (e.g. Thermal decomposition is when a molecule breaks up due to being heated)
Oxidation (adding oxygen or losing electrons)
Reduction (removing oxygen or gaining electrons). Note that some reactions involve BOTH oxidation and reduction!
… If a substance is OXIDISED, this means that…?
… If a substance is REDUCED, this means that…?
… Decomposition reactions are a type of chemical reaction that involves breaking down a compound into smaller compounds or individual elements.
… When an ionic substance is dissolved in water, we describe the whole thing as a ‘solution’ with the state symbol (aq) meaning ‘aqueous’. Solutions will always be clear (transparent), but they may be coloured.
If you cannot see through a liquid, then it is likely to be a mixture of a liquid with fine solid particles (a precipitate).
… A solution is made when a solute (solid) dissolves into a solvent (a liquid). For example, sodium chloride (table salt) dissolves in water to make a solution of sodium chloride.
… Balancing chemical equations by writing an element list under the reaction arrow and counting the numbers of atoms on each side.
Useful hint: If you count a “3” for one type of element, try making it into a “4” by placing a multiplier of 2 in front of one of the reactants or products.
Note that when balancing equations, we can only place multiplier numbers in FRONT of each reactant or product – we cannot change the formula of the compound or element.
For example, magnesium oxide has the formula MgO. We cannot put a number in front of the O (e.g. Mg2O) because that would change the compound.
When you have finished balancing the equation, check if you can cancel down by dividing all the balancing numbers by 2… This doesn’t happen very often, but it’s worth checking 🙂
Fundamental ideas
… An element is a substance made up of the same type of …?…
… A compound is two or more …?… bonded together
… A mixture is two or more compounds or elements that are NOT bonded together. These can usually be separated, for example, using filtration.
… In chemistry, a pure substance is a single element or compound, not mixed with any other substance.
… Pure elements and compounds melt and boil at specific temperatures. Melting point and boiling point data can be used to distinguish pure substances from mixtures.
… Note that in everyday language (i.e. not chemistry language), a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk.
… You may be asked to use melting point and boiling point data to distinguish pure from impure substances.
… A formulation is a mixture that has been designed as a useful product. Many products are complex mixtures in which each chemical has a particular purpose. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties. Formulations include:
fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
Atomic Structure
… The tiny …?… at the centre of an atom is made up of positive …?… and neutral …?…
… Negatively charged …?… orbit the nucleus.
… Protons have a charge of …?…
… Electrons have a charge of …?…
… Neutrons have no …?… (they are NEUtral)
… The Atomic number tells us the number of…?
… The Mass number (the bigger number) tells us…?
… We can calculate the number of neutrons in a nucleus by…?
Forming bonds
… In an atom of an element, the number of protons (…?… charged) balances the number of electrons (…?… charged). This means that the atom is electrically neutral (no charge)
… If one or more electrons are removed from a metal atom, the atom becomes p…?… charged and is now called a positive i…?…
… If one or more electrons are transferred to a non-metal ion, the non-metal atom becomes n…?… charged and is now called a negative i…?…
… Atoms will always lose or gain electrons to form charged ions that have a full outer shell of electrons (this makes them stable and have the same electronic configuration as the noble gases).
… Metals can react with non-metals to form i…?… compounds. This is when the non-metals ‘steal’ …?… from the metals.
The non-metal atom becomes electrically unbalanced to become a …?… charged ion.
The metal atom becomes a …?… charged ion.
The two oppositely charged ions attract each other with a strong e…?… bond.
Non-metals bond with each other by s…?… each other’s electrons. This forms c…?… bonds.
… A “dot and cross diagram” can show the outer electron configuration in both ionic and covalent bonding.
… A molecular formula simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together.
For example, the molecular formula of butane is C4H10, and the molecular formula of ethanol is C2H6O.
… A structural formula shows how the various atoms are bonded. There are various ways of writing a structural formula, for example: C2H5OH or CH3CH2OH
… A displayed formula shows all the bonds in the molecule as individual lines. Each line represents a pair of shared electrons (a single covalent bond).
Rocks and building materials
The limestone cycle
… Limestone is calcium …?…, made from dead animal skeletons which have fallen to the bottom of the sea and have been crushed together over thousands of years.
… Limestone is used for b…?… materials, but is eroded by …?… rain.
… Thermal decomposition of limestone occurs when you h…?… strongly. The product is calcium …?… (quick lime)
… Adding …?… to calcium oxide forms ‘slaked lime’ or calcium h…?… solid.
… Slaked lime (a solid) can be used to reduce soil’s acidity which certain crops may need.
… Slaked lime plus water makes a solution called ‘lime water’ (calcium h…?…) which is an a…?… The chemical formula of lime water is Ca(OH)2
… Bubbling carbon dioxide through lime water produces solid Limestone again as a fine p…?… (cloudy ‘dust’). This is a test for carbon dioxide.
… We also looked at the ‘state symbols’ (s), (l), (g) and (aq) which describe whether a substance in a solid, liquid, gas or aqueous solution (I.e. dissolved in water).
… How is cement made?
… How is mortar made and what is it used for?
… Concrete is made by adding ….?… (crushed rock) to mortar.
… Some social and environmental advantages and disadvantages of quarrying and cement works are…?
… What causes acid rain?
… Why is acid rain bad for some buildings?
Carbonates
… A salt is an ionic compound of a metal with a non metal(s).
… Carbonates are salt compounds of a metal and a CO3 group.
… Carbonates react with acids to form a s…?…, …?… and …?…
… Thermal decomposition is when a compound is b…?… d…?… by h…?… it strongly.
… Carbonates undergo thermal decomposition when heated to form a metal o…?… plus …?… gas, for example:
Calcium carbonate (limestone) —-> …?… (quicklime) + …?….
Metals and their uses
Extracting metals
… Extracting metals by heating with carbon (reduction reaction to remove oxygen from the metal ore). This only works with metals that are less reactive than carbon.
… Reduction reactions produce carbon dioxide which is a greenhouse gas.
… Smelting of copper ore is done by heating the ore in air with carbon. The two reactions that occur in smelting are:
A d…?… reaction to produce the metal oxides, and
A r…?… reaction to displace the oxygen using carbon.
Note that the first reaction also produces s…?… d…?… which causes acid rain.
… A displacement reaction is when a more reactive metal ‘displaces’ a less reactive metal from its compound.
For example, bubbling chlorine through a solution containing bromide ions will displace the bromide ions forming the element bromine. Chlorine is a more electronegative element than bromine (it has more attraction for an electron to fill its outer shell because it is a smaller atom with fewer electron shells).
Making Iron – The Blast Furnace
… Iron ore is called …?… and is made up of iron …?… and other impurities such as…?
… In a blast furnace, iron oxide is r…?… by carbon …?… to produce iron.
… Why is limestone also added to the coke (carbon) and iron mixture?
… Write a balanced symbol equation for the reduction of iron (III) oxide by carbon.
… Iron produced directly from the blast furnace is too …?… for most uses. It can be converted into steel by…?
… Steel is an a..?… of iron (a mixture of metals) containing different quantities of c..?… and other elements depending on the use (e.g. car bodies to cutting tools).
… Phytomining: using p…?… to draw up copper from areas which would be u…?…. to mine traditionally (low grade ore). The plants are b…?… in air and reacted with s…?… acid. Scrap …?… can then be used to react with the solution to produce copper metal (or electrolysis).
… Bioleaching is similar but using bacteria which feed off the copper ore. The resulting ‘leachate’ can be reacted with iron, or electrolysis can be used to release the copper metal.
… Cost is an important factor in the extraction of metals. You can certainly use cost as a valid point in your answers, but make sure that you go into DETAIL. For example, “the cost of extracting Aluminium from its ore is much more than from recycling because more energy is needed”.
… Aluminium is extracted using electrolysis because the usual method of reacting an ore with carbon (to displace the metal) won’t work. This is because carbon is …?… reactive than Aluminium.
… Copper can be purified (e.g. for use in electrical cables) using electrolysis.
Uses of metals
… An alloy of a metal is usually stronger than the pure metal because…?
… Shape memory alloys can be ‘programmed’ to turn to a certain shape when heated to a certain temperature.
… Iron can contain small amounts of carbon which make it into Steel which is harder and stronger. Adding other metals to the steel to make it an alloy can give it other properties like resistance to corrosion (stainless steel).
… Three types of steel include low carbon, high carbon and stainless steel. Their properties are…?
… Aluminium and titanium are strong and have a low d…?… Alloys of these metals are very light and strong and resistant to c…?… – very useful for aeroplane construction and medical implants.
Metallic Issues
… Mining for metal ores involves digging up and processing large amounts of rock. This can produce large amounts of w…?… material and effect large areas of the …?…
… Recycling metals saves the e…?… needed to extract the metal.
… Recycling also saves resources because less o…?… needs to be mined. Also, less f…?… fuel is required to provide energy for extracting the metal.
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Life cycle assessment and recycling
Life cycle assessments (LCAs) are carried out to assess the environmental impact of products in each of these stages:
• extracting and processing raw materials
• manufacturing and packaging
• use and operation during its lifetime
• disposal at the end of its useful life, including transport and distribution at each stage.
At each stage use of water, resources, energy sources and production of some wastes may occur. Polluting effects may be more difficult to define, so may be more of a subjective judgement.
It’s worth bearing in mind that LCAs can be devised to evaluate a product but these may be misused to form biased conclusions, for example, for advertising purposes.
Questions may ask you to carry out simple comparative LCAs for shopping bags (or similar) made from plastic and paper.
Our changing planet
… The gases in the early atmosphere are believe to have been mostly c…?… …?…, n…?… and w…?… …?…, with smaller amounts of …?… and …?… .
These gases are thought to have been released into the Earth’s early atmosphere by …?… eruptions.
… As the Earth cooled, water vapour c…?… to form the …?…
… Many scientists have suggested theories of how life on Earth began, but no one knows for sure because we have insufficient e…?…
… As plants spread over the earth, the levels of c…?… …?… in the atmosphere decreased because …?
… Most of the carbon dioxide in the early atmosphere became ‘locked up’ in s…?… rocks and f…?… f…?… . How did this process occur?
… The air we breathe today is made up of about 20% …?… and 80% …?…, with very small amounts of …?.. and …?…
… The main gases in air can be separated by …?… …?… because the gases have different …?… …?… These gases are used in …?… as raw materials
… For about 200 million years, the amount of …?… …?… in the atmosphere has remained about the same. This is because the natural processes which move this gas into and out of the atmosphere had achieved a b…?…
… How does the greenhouse effect work and which gases are mainly responsible for it?
… What are two processes that release carbon dioxide into the atmosphere, and two processes which remove it?
… What are two processes that release methane into the atmosphere?
The structure of the Earth:
… What are the names of the layers of the Earth that are solid?
… The high temperatures in the Earth’s core and mantle are due to the …?… decay of elements.
… The crust is really …?… compared to the other layers (only about 5-70km)
… All the materials and other resources that we depend on come from the …?…, the …?… and the atmosphere. For this reason, they are in limited supply and should be …?…
… Tectonic plates move a few …?… each year due to …?… …?… in the Mantle (underneath the ‘floating’ plates).
… Where plates meet, huge forces build up causing …?…, …?… or mountains to form.
… Why can scientists not predict when and here’re earthquakes will happen?
… Alfred Wegener proposed his theory of continental drift a hundred years ago but there was not enough …?… for scientists accept his ideas until about the 1960s. Here is a photo of Alfred Wegener: http://en.wikipedia.org/wiki/Alfred_Wegener