Chemistry: How Much?
- Created by: William Page-Brown
- Created on: 10-04-13 17:09
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- Chemistry: how much?
- the mole
- 6.023 x 10 to the 23
- mole of atom or molecule weighs exact same in grams as relative atomic mass
- number of moles = mass in g / relative formula mass
- relative masses are compared to carbon 12
- reacting masses and empirical formulas
- 42.9g of K in 61.6g KOH
- 42.9 / 61.6 x 100 = 60.6%
- simplest ratio of atoms in a compound
- chemical formula - C6H12O6
- empirical formula - CH2O
- concentration
- moles per dm3
- concentration = number of moles / volume
- mass = number of moles / relative formula mass
- GDA's per 100g or 100ml
- use sodium content to estimate mass of salt
- titrations
- add alkali to conical flask
- add three drops of indicator
- fill a burette with the acid
- add acid to alkali slowly
- indicator changes colour when neutralised
- record volume of acid needed
- should try to get several consistent readings
- use single indicators to find exact point
- start with 25cm3
- concentration is 0.100 moles per dm3
- takes 49cm3 to neutralise
- gas volumes
- gas syringe
- upturned measuring cylinder or burette
- measure on scales
- one mole of gas occupies 24dm3
- following reactions
- reactions stop when one reactant is used up
- reactant used up is limiting reactant
- product is directly proportional to limiting reactant
- more reactant particles from more reactant
- steeper curves mean faster reactions
- more limiting reactant creates a faster reaction time
- equilibrium
- the products of the reaction can themselves react to produce the original reactants
- when both reactions are at the same rate, there is an equilibrium
- this can only happen if the products cannot escape
- effects: temperature, pressure, concentration
- on left - more reactants
- on the right - more products
- changing equilibrium
- if you decrease temperature, equilibrium increases it
- if you increase pressure, equilibrium tries to decrease it
- if you increase concentration, equilibrium makes more products
- the contact process
- used to make sulfuric acid
- make sulfur dioxide
- sulfur dioxide oxidised
- sulfur trioxide makes sulfuric acid
- uses 450 degrees temperature
- one atmosphere used
- catalyst is used which doesn't affect the equilibrium
- strong and weak acids
- acids produce protons in water
- strong acids ionise completely in water
- weak acids do not fully ionise
- ionisation of the weak acid is a reversible reaction
- strong acids have a pH of one or two
- weak acids have pH of five or six
- strong acids are better electrical conductors as they have more ions
- strong acids react faster
- precipitation reactions
- ionic substances must be liquid
- a solid precipitate is formed
- chloride - white
- bromide - cream
- iodide - yellow
- preparing insoluble salts
- mix all ions
- precipitate, filter, and dry
- put onto paper and leave to dry
- the mole
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