Amount of substance

The amount of substance (n) is used to quantify the amount of particles in a substance, measured in moles (mol). One mole is the amount of substance that contain 6.02 x 10²³ particles. 6.02 x 10²³ is known as avogadro's constant. 12g of carbon-12 contains 6.02 x 10²³ particles. This means 1 mol of carbon-12 would weigh 12g. Therefore the mass of a substance is given by the amount of it in moles multiplied by its molar mass, which is usually the atomic mass. One mole of anything, be it particle or element is always 6.02 x 10²³ of it. Multiply the amount of the substance by avogadro's constant to find the number of particles that make up that substance.

Molecular formulae - covalent compounds are made up of molecules. The molecular formulae is number of atoms of each element in a molecule.

Empirical formulae - Empirical formula is the simplest whole number ratio of atoms in an element. It is useful for componds that do not exist as a single molecule. These include metals, some non-metals and ionic compounds. These form giant lattice structures.

Relative molecular mass - The weighted mean mass of a molecule compared with 1/12 of carbon-12. The relative molecular mass can be found by adding the relative atomic masses of each singular atom in the molecule.

Relative formula mass - The weighted mean mass of a formula unit compared with 1/12 of carbon-12. The relative formula mass can be found by adding the relative atomic masses of each singular atom in the formula unit.

To find empirical formula from mass- divide mass by the molar mass to get moles, find the simplest whole-number ratio of those moles, write the ratio as an empirical formula

To find molecular formula from percentages- divide percentage by the molar mass, write the simplest whole-number ratio and empirical formula, divide relative molecular mass by the relative mass of the empirical formula, multiply the empirical formula by the result to find molecula formula.

Hydrated salts have water that is part of its structure. The water of crystalisation of a salt is the amount in moles of water that makes up the crystal. When hydrated salts are heated, bonds holding the water inside the crystal will break, allowing the water to evaporate and leaving an anhydrous salt behind, usually with a different colour. With hydrated copper (II) sulfate the colour changes from blue to white. The water of crystalisation is shown in a formula with a dot seperating the salt and water. For copper (II) sulfate it is CuSO₄()5H₂O_(s) --> CuSO_4(s) + 5H₂O_(l). Without water, the crystal structure is lost and a white powder remains.

Formula of a hydrated salt- find the mass of the anhydrous salt by subtracting the mass of the crucible by the final mass, find mass of the water by subtracting the final mass from the intitial mass, find the amount of water in moles, find the simplest whole number ratio, find x and write the formula of the hydrated salt.

Assumptions- all of the water has been lost, no further decomposition.

Volume in chemistry is measured in dm³. 1dm³ = 1000cm³ = 1000ml = 1 litre, l

Solutions have concentrations, which are measured in mol/dm³ or g/dm³, convert by multiplying or dividing by molar mass. conc is given by amount divided by volume

A standard solution is a solution of known concentration. To make a standard solution: work ou the moles required of the solvent, work out the molar mass of the solvent, and then use both to work out the mass in g of solvent required.

Molar gas volume is the volume per mole of gas molecules at stated temperature and pressure. RTP is 293 K, and 101 kPa. STP is 298K and 100 kPa. The volume or moles of gas can be worked out by using pV = nRT, where R is the ideal gas constant. Rearrange to find a value. Assumptions: random motion, elastic collisions, negligible size, no intermolecular forces.

In a balanced equation, the balancing numbers give the ratio of the amount of each substance. The ratio is the stoichiometry of the equation. It is used to find the amounts of each reactant and the amount of each product, which is given as a ratio by the balancing number

Percentage yield: the actual yield of a substance is always lower than the theoretical yield. This is because of factors such as an incomplete reaction, side reactions, and loss of product during purification and transfer. The percentage yield is given by the theoretical yield over the actual yield multiplied by 100 to give a percentage.

Atom economy: the atom ecomony of an equation is a percentage showing how well the atoms in the reaction have been utilised to give desirable products. Atom economy is given by the sum of molar masses of all desirable products over the sum of molar masses of the total products, multiplied by 100 to give a percentage