C5a&c - Moles and empirical formulae & Quantitive
No. of Moles = Mass(g) / Molar Mass(g) (relative formular mass)
Mass = No. of Moles X Molar Mass
Molar Mass = Mass / No. of Moles
Empirical formulae (e.g. C6H1206 = CH2O)
Concentration = Moles / Volume (dm^3)
Moles = concentration X Volume
Volume = moles / concentration
cm^3 / 1000 = dm^3
g/dm / Molar mass = mol/dm^3
C5b - Electrolysis
Electrolysis is the decomposition of the liquid eletolyte, by passing a current through it. Moving ions transfer charge in the eletrolyte whilst electrons transfer charge in the wire.
+ions (Cation) accept electrons at the cathode and are discharged, they then move through the eletolyte and transfer charge. The now -ions (anion) are now attracted to the Anode where they give up the electrons before becoming discharged in to the eletrolyte again.
- Anode - + electrode
- Anion - - Ions (onions, crying, sad, negative)
- Cathode - -electrode
- Cation - +ions (pussytive)
H+ and OH- are always present in aq. solutions.
Mass gained at Cathode = Mass lost at Anode
AN OILRIG CAT
ANode Oxidation Is Loss Reduction Is Gain Cathode
C5b - Electrolysis Continued...
Metal ions (& hydrogen) are positive
non-Metal ions are negative
Q=IT (Charge = Current X Time)
Amount deposited on Cathode (removed from Anode) increases proportionaly with both time and current.
C5d - Titrations
Titration allows you to measure the amount of a substance present in a solution
Titration curve: Equivalence point = neutralisation point = 25cm^3, Acid to Alkali
Titre = volume needed to neutralise
C5e - Gas volumes
- Gas syringe
- Upturned burette filled with water
- Upturned measuring cylinder filled with water
Reactions stop when one of the reactants is used up. The reactant used up first is called the limiting reactant, the other/s is called the excess
A mole of gas at room temperature and pressure has a volume of 24dm^3
Volume (dm^3) = number of moles X 24
C5f - Equilibria
Equilibria = reversible reactions – forward and backward reactions are equal Equilibrium = reversible reactions proceeds at the same rate in a closed system Reactants ............ concentration is greater then reactants - Equilibrium - Right Concentration is greater then product ............ products - Equilibrium - Left Add more product or remove reactant - reaction shifted to the left Remove product or add more reactant - reaction shifted to the right Increasing pressure moves equilibrium to the side with the least no. of moles of gas
C5g - Strong and weak acids
Acids ionise in water to produce hydrogen ions (H+).
- higher electrical conductivity (more H+ available to carry charge)
- Produces gas rapidly when reacting with magnesium or calcium carbonate (higher concentration of H+ causes more collisions between acid and ^)
- Lower pH (the higher the H+ the lower the pH
- Higher concentration of hydrogen ions
- Ionises completely in water to form ions and no molecules are present
Weak acids - (opposite to strong)
- Ionises slightly in water and produces an equilibrium mix containing acid molecules and ions