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Science C2 Topic 6

Edexcel GCSE additional science chemistry: quantitative chemistry

QuestionAnswer
How do you calculate relative atomic mass and what is it? Relative atomic mass is the mass of an atom of a particular element compared to the mass of a 12C atom, taking into account the relative abundance of the isotopes RAM = (percentage of isotope X mass number) + ( percentage of isotope X mass number)...
What is relative formula mass? The sum of the relative atomic masses of all the atoms in a compound
What is a molecular formula? The true formula for a simple compound- i.e. the exact numbers of atoms of each element in the compound
What is empirical formula? The simplest whole-number ratio of the number of atoms or ions of each element in a molecule
What are the empirical formulae for the following: C2H4, C10Na6Li, Ca5H15 C2H4 --> CH2 ... C10Na6Li --> C10Na6Li ... Ca5H15 --> CH3
What is the empirical formula when there is 24% carbon, 48% oxygen and 28% silicon? Ca2O3Si
How do you calculate the percentage by mass of a given element in a compound? % by mass = (number of atoms of element in compound X RAM of element / RFM ) X 100
What is the percentage by mass of oxygen in CaCO3? 48%
Work out how much aluminium oxide is produced when 135g of aluminium is burned in oxygen 255g
What is the yield of a reaction? The mass of useful product obtained from the reaction
What is the difference between the theoretical and actual yield? The theoretical yield is the maximum useful product that could be obtained- the actual yield is the mass of useful product obtained in an experiment
Why is the actual yield usually less than the theoretical yield? * competing side reactions use up some of the reactants * incomplete reactions * some of the reactants or products may be lost during practical preparation
What is the percentage yield and how do you calculate it? The percentage yield compares the actual and theoretical yields- percentage yield = (actual yield / theoretical yield) X 100
What are the by-products of a reaction? The additional substances produced in a chemical reaction that are unwanted
What are waste products? Unwanted, useless by-products of a reaction
What are some issues associated with the disposal of waste products? * expensive to treat, transport, make safe * environmental problems e.g. fertilisers running into streams * social problems e.g. smells
What are the features of the most economically favourable reactions? * percentage yield is high * fast reaction * no waste products (only by-products that are useful)
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