Chemical Changes Flashcards
Oxidation
oxygen reacts with a substance to make a new compound
Reactions of metals with water
metal + water –> metal hydroxide + hydrogen`
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Potassium, Sodium ,Calcium , Magnesium, Aluminium, Carbon ,Zinc , Iron ,Tin , Lead , Hydrogen , Copper ,Silver, Gold
OILRIG
Oxidation Is Loss of electrons
Reduction is Gain of electrons
Magnesium Oxide
white
Copper Oxide
green
Iron hydroxide
rust
metal + acid =
salt + hydrogen
metal carbonate + acid
salt + carbon dioxide + water
metal alkali + acid
salt + water
If something is acidic it contains what
hydrogen ions
If something is alkaline it contains what
hydroxide ions
What happens when acids are added to aqueous solutions
they ionise to produce hydrogen ions
Strong acids
completely dissociate
Weak acids
partly ionise
Strength
measure of hydrogen ions
Concentration
grams or moles per dm³
Neutralisation Reaction
H+(aq) + OH-(aq) arrow H2O(l)
Electrolysis
the process of decomposing a liquid ionic compound by passing a direct electrical current through it
PANIC
Positive Anode Negative is Cathode
Cation
positive ion
Anion
negative ion
Cathode Half Equations
Na + e- arrow Na
Anode Half Equations
2Cl- arrow Cl2 + 2e-
Why is it electrolysis expensive ?
high temperature is needed to break ionic bonds as a lot of energy is needed to break bonds
M.P of aluminium ore (brauxite)
2050 degrees celsius
Electrolysis of Alumium
the ore is dissolved in a compound called cryolite which lowers the m.p to 700 degrees Celsius and makes it cheaper.
Solution
it is dissolved in water
Hydroxide ions….(when oxygen forms at the electrode)
4OH- arrow H20 + 02 + 4e-
give up electrons more easily than Sulfate ions so oxygen forms.
Molten
means it has been melted
Aqueous
it has been dissolved in water
Electrolysis is Aqueous Solutions Cathode
is the metal electrolyte more reactive than hydrogen
if yes = then hydrogen gas is produced
if no = then that metal is produced (copper ,gold , silver or platinum)
Electrolysis is Aqueous Solutions Anode
is the negative ion in the electrolyte a halide ?
if yes = then that halogen gas is produced at the ANODE !
if no = then oxygen gas is produced
Neutralising an alkali with an acid, titration could be used to calculate the concentration of the alkali
The concentration of the acid to be added
The volume of the alkali
If both the acid and alkali are strong, suitable indicators would be:
Methyl orange (yellow in alkali → red in acid). Phenolphthalein (pink in alkali → colourless in acid).
Titration
1) Use the pipette and pipette filler to add a measured volume of sodium hydroxide solution to a clean conical flask.
2) Add a few drops of indicator and put the conical flask on a white tile.
3) Fill the burette with hydrochloric acid and note the starting volume.
4) Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5) Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). 6) Note the final volume reading.
Repeat steps 1 to 5 until concordant titres are obtained. More accurate results are obtained if acid is added drop by drop near to the end-point.
