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Chemistry 1.3
AS edexcel chemistry - formulae, equations, amounts
Question | Answer |
---|---|
What is an atom? | The smallest particle of a chemical element |
What is an element? | A substance that can't be broken down into anything simpler |
What is an ion? | A species that has gained or lost electrons so has a positive or negative charge |
What is the difference between a compound and a molecule? | A compounds is two or more atoms of different elements that are chemically bonded together. Molecules can be atoms of the same or different elements. |
What is the molar mass? | The mass of one mole of a substance, ie Mr or Ar in grams, units are g/mol |
What is a mole? | The mass of an element equal to its relative atomic mass in grams, which contains 6.02 x 10^23 atoms - Avogadro's number. Amount is measured in moles |
What is the relative atomic mass? | The weighted average mass of an atom of an element divided by 1/12th the mass of a carbon 12 atom |
How do you form an ionic equation? | All aqueous substances are written out as ions as ions move freely in solution, but gases, liquids and solids remain unchanged. Spectator ions (ions that don't change in the reaction) are omitted from the equation. State symbols and charges included. |
What are the solubility rules for ionic compounds? | All nitrates are soluble, all sulphates are soluble except barium lead and calcium, all chlorides, bromides and iodides are soluble except lead and silver, all carbonates and hydroxides are insoluble except ammonium, sodium and potassium |
What is the molecular formula and empirical formula? | Molecular: the exact number of atoms of each element present in a molecule. Empirical: simplest whole number ratio of atoms of each element in a molecule. |
How do you get an empirical formula from a molecular formula? E.g. C4H8O16, C2H7OH | Decrease ratio to its simplest form - CH2O4, C2H7OH |
How do you calculate an empirical formula from percentages/ masses of elements? E.g. when there is 60% carbon, 13.3% hydrogen and 26.7% oxygen | Draw up a table with the headings: element, mass (g), mass/Ar, ratio. C3H8O |
How do you calculate a molecular formula from a given empirical formula and molar mass? E.g. C2H5, molar mass is 87 | Work out empirical mass, divide molar mass by empirical mass, increase ratio by this value. C6H15. |
What is the yield, actual yield, theoretical yield and percentage yield? | Yield is the mass of useful product obtained from a reaction. Theoretical - maximum mass of useful product obtained when all reactants react. Actual - mass of useful product obtained from an experiment. % = actual / theoretical x 100 |
What is atom economy and how do you calculate it? | A measure of what proportion of products are useful and how much is waste. Atom economy = mass of useful product / total mass of product x 100 |
Metal + acid -> ? | Salt + hydrogen |
Metal oxide + acid -> ? | Salt + water (neutralisation) |
Carbon dioxide, salt and water is produced from which reactions? | Neutralisation reactions - metal carbonate + acid or metal hydrogencarbonate + acid |
Ammonia + acid -> ? | Ammonium salt |
Metal + water ->? | Metal hydroxide + hydrogen |
Number of molecules of a substance = ? | Amount in moles x Avogadro's constant (6.02 x 10^23) |
Amount of a substance = ? | Concentration x volume, or mass / molar mass |
Concentration of a solution = ? | Amount / volume or mass / volume |
Amount of gas = | volume / gas molar volume. At RTP this is volume / 24 |
What is a gas molar volume? | Volume occupied by 1 mol of gas molecules |
What is Avogrado's law for gases? | 1 mol of any gas occupies the same volume under particular temperature and pressure |
In a reaction between methane and oxygen 60 cm3 of methane was burnt with 60 cm3 of oxygen at RTP. What is the composition of the gas mixture produced? | Final volume = 60 cm3 (30 cm3 CO2 + 30 cm3 CH4) |
What is a hydrated salt and an anhydrous salt? | Hydrated - contains water molecules within the lattice. Anhydrous - no water present. |
How do you work out the relative number of water molecules e.g. CuSH6O7 | CuSO4.3H2O. Use number of hydrogen atoms to work out relative number of water molecules |