Iron

Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as haematite contain iron oxide. The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction...

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Crystallising salt solutions

You may be asked to describe how to make a soluble salt. If the base dissolves in water, you need to add just enough acid to make a neutral solution. Check a small sample with universal indicator paper. If ammonia solution is used, you can add a little more than needed to get a neutral solution. Warm...

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Naming salts

The name of the salt produced in a neutralisation reaction can be predicted. The first part of the name is 'ammonium' if the base used is ammonia. Otherwise, it is the name of the metal in the base. The second part of the name comes from theacid used: Chloride (if hydrochloric...

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Making soluble salts

You need to be able to describe the reactions of acids with bases and metals. You should be able to work out the particular salt formed in the reaction. Acids and bases When acids react with bases, a salt and water are made: acid + metal oxide → salt + water acid + metal hydroxide...

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Neutralisation reactions

Ions are charged particles which are formed when atoms, or groups of atoms, lose or gain electrons. For the examination, you need to know which ions are produced by acids, and which are produced by alkalis. You will also need to know the ionic equation for neutralisation. State...

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Acids, bases and salts

Acids have a pH of less than 7. Bases have a pH of more than 7. When bases are dissolved in water, they are known as alkalis. Salts are made when an acid reacts with a base, carbonate or metal. The name of the salt formed depends on the metal in the base and...

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Reversible reactions

In reversible reactions, the reaction in one direction will be exothermic and the reaction in the other direction will be endothermic. The decomposition of ammonium chloride is a reversible reaction: ammonium chlorideammonia + hydrogen chloride Ammonium...

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Endothermic reactions

These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are: Electrolysis The...

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Energy changes and reversible reactions

Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings. Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse...

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Collisions and reactions

You will be expected to explain, in terms of particles and their collisions, why changing the conditions of a reaction changes its rate. Collisions For a chemical reaction to occur, the reactant particles must collide. Collisions with too little energy do not produce a reaction. The...

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Factors affecting the rate

You will be expected to remember the factors that affect the rate of reactions, and to plot or interpret graphs from rate experiments. How to increase the rate of a reaction The rate of a reaction increases if: The temperature is increased The concentration of...

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Rates of reaction

The rate of a reaction can be measured by the rate at which a reactant is used up, or the rate at which a product is formed. The temperature, concentration, pressure of reacting gases, surface area of reacting solids, and the use of catalysts, are all factors...

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Empirical formula - Higher tier

You can use information about reacting masses to calculate the formula of a compound. Here is an example: Question Suppose 3.2 g of sulfur reacts with oxygen to produce 6.4 g of sulfur oxide. What is the formula of the oxide?   Use the fact that the...

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Reacting masses calculations - Higher tier

If you have a balanced equation for a reaction, you can calculate the masses of reactants and products. Sample question Look at this equation: CaCO3(s)    →    CaO(s) + CO2(g) If we have 50g of CaCO3, how much CaO can we make? First, work out the Mr values for the...

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Reversible reactions

Many reactions, such as burning fuel, are irreversible - they go to completion and cannot be reversed easily. Reversible reactions are different. In a reversible reaction, the products can react to produce the original reactants again. When...

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Percentage yield

The principle of conservation of mass lets you calculate the theoretical mass of product expected in a chemical reaction. However, it is not always possible in practice to get the entire calculated amount of product. This is because: Reversible reactions may not go to completion Some product...

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Conservation of mass

Conservation of mass Mass is never lost or gained in chemical reactions. We say that mass isconserved. In other words, the total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning. This fact allows you to work out the...

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Quantitative chemistry

You should be able to calculate the masses of reactants and products from balanced equations, and the percentage composition by mass of an element in a compound. Higher tier students should also be able to calculate the percentage yield of a reaction, and...

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