section 1 chapter 2 amount of substance oxford aqa

reltive atomic mass

weighted average mass of an atom of an element, taking into account its naturally occurring isotops. in comparison to 1/12 the relative atomic mass of a carbon 12 atom

relative molecular mass

mass of a molecule compared to 1/12 the relative atomic mass of a carbon 12 atom

why is carbon 12 the standard

when a mass spectrometer was used on carbon 12 1/12 of carbon 12 is exactly 1 hence is the standard used by all chemists

what term is used for ionic compounds because they do not exist as molecules

relative formula mass

how does the Mr and the mass correlate

if Mr = x

then mass =x grams

e.g helium= 4 so the mass is 4 g

the avogadro constant and how to calculate the number of moles using the constant

the number of atoms in 12g of carbon 12

the number of particles in a mole

how to calculate mass using Avogadros constant and the Ar

how to calculate moles

how to calculate concentration using volume and moles

units

concentration mol/dm³

n=mol

volume= dm³

the ideal gas equation

gas equation given room temperature and pressure

what is the empiricle formula

the simplest whole number ratio of the atoms of each element present in a compound

how to find the empiricle formula

• find the masses

• find the number of moles

• convert the moles into whole number ratios

molecular formula

actual number of atoms of each element in one molecule of the compound

e.g C2H6(molecular) is CH3 (empiricle)

how tofind the units of the empiricle formula using the molecular formula

divide the relative molecular mass by the relative mass of the empiricle formula

stoichiometry

the ratio in which the reactants react and the products are produced in simple whole numbers

spectator ions

ions that do not take part in the reaction

how to write an ionic equations

• An ionic equation shows only the ions or other particles taking part in a reaction, without showing the spectator ions

step 1 Write the chemical equation

STEP 2: Rewrite by separating the soluble ionic compounds into their dissociated ions

step 3 Cancel out common ions, which are the spectator ions

STEP 4: Write the net ionic equation for neutralisation

atom economy

The atom economy of a reaction shows how many of the atoms used in the reaction become the desired product

Economic, ethical and environmental advantages for society and for industry of developing chemical processes with a high atom economy.

A high % yield does not always mean the reaction is efficient.

The higher the % atom economy, the cheaper the process

The higher the % atom economy, the less wasteful the process.