What ions do acidic solutions contain?
High concentrations of hydrogen ions (H+)
What ions do alkaline solutions contain?
High concentrations of hydroxide ions (OH-)
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What ions do acidic solutions contain?
High concentrations of hydrogen ions (H+)
What ions do alkaline solutions contain?
High concentrations of hydroxide ions (OH-)
What are bases?
Any substance with a pH above 7.
Define alkalines.
Bases that can dissolve in water.
What is neutralisation?
A reaction between an acid and alkali to produce salt and water.
What is the formula for a neutralisation reaction?
Acid + alkali → salt + water
What is the symbol equation?
H+ + OH¯ → H₂O
What are the 3 strong acids we need to know and their symbols?
Hydrochloric Acid: HCl
Sulfuric Acid: H2SO4
Nitric Acid: HNO3
Define acid concentration
How many H+ ions there are in a volume (dilute or concentrated)
Define acid strength
How much an acid ionises (strong or weak)
What is pH scale?
A measure of the concentration of hydrogen ions.
What is the formula for increasing H+ ion concentration?
10-pH
List the reactivity series (how can it be remembered)
Potassium - Please
Sodium - Stop
Calcium - Calling
Magnesium - My
Aluminum - Aunt
Zinc - Zelda
Iron - Ironic
Tin - Too
Lead - Little
Copper - Compliments
Silver - Sound
Gold - Groovy
How does potassium react with water?
Burns as a lilac firm on the surface of the water.
What is the word and symbol equation?
Potassium + water → potassium hydroxide + hydrogen
K + 2H₂O → K(OH)₂ + H₂
Define dissociation
When ions in acids separate when dissolve in water.
What happens to strong acids in water?
Strong acids completely ionise in water.
Show the equation for the ionisation of strong acids in water.
Strong acid → Hydrogen ions + other ions
Why do strong acids complete ionise?
Lots of hydrogen ions mean acids react quickly with the water causing a lot of collisions which separates the ions.
What happens to weak acids in water?
Weak acids only partially ionise.
What is the equation for the ionisation of weak acids?
Weak acid ⇌ Hydrogen ions + other ions
How can a base by identified?
A -oxide or -hydroxide substance e.g. MgO or NaOH
Define reactivity.
A measure of how violently and readily a substance will react with another substance to stabilise its own outer shell.
Define displacement
A more reactive metal takes the place of the less reactive metal in a compound.
What happens when an acid and metal carbonate react?
Acid + metal carbonate → Salt + water + carbon dioxide
What happens when an acid and metal react?
Acid + metal → salt + hydrogen
What are the four common salts and their symbols?
Sulphate = (SO4)-2
Phosphate = (PO4)-3
Nitrate = (NO3)-
Chlorine = Cl-
How do we determine the salt made?
Metal/carbonate/base name & acid as salt + water
E.g. zinc chlorine + water
Example ; what are the products of sulfuric acid and copper oxide reaction?
Copper sulphate + water
Practical; how do we make soluble salts using an insoluble base?
Gently warm the acid solution using a Bunsen burner and tripod apparatus and turn off.
Add the insoluble base to the acid a bit at at time until no more reactants are in excess and no more can be dissolved.
Use filtration method to filter any excess solids.
Gently heat the solution again using a water bath and evaporating basin until only half remains.
Turn off and pat dry.
Leave to dry until crystals from then pat dry.
Define an ore
A type of rock that contains metal compounds stored as oxides.
Define oxidation
The reaction between a metal and oxygen.
Define reduction.
The reaction which separates a metal from its oxide.
How are metals extracted from their ores?
Metals less reactive than copper = found naturally in the ground.
Metals more reactive than copper, less reactive than carbon = reduced using carbon (heating) which displaces the oxygen to make carbon dixode and the metal.
More reactive than carbon = electrolysis
Define oxidisation and reduction (OILRIG)
Oxidation
Is
Loss of electrons (gain of oxygen)
Reduction
Is
Gain of electrons (loss of oxygen)
How can we determine what is oxidised and what is reduced?
The metal atom is always oxidised.
The metal ion (in a compound) is always reduced.
What change of states occur during redox reactions?
A solid metal atom (s) to a metal ion (aq)
A metal ion (aq) goes to a metal atom (s)
What determines how many electrons are lost?
The group of the element I.e. group 2 needs to lose 2 electrons to stabilise the outer shell as it is a positive 2+ ion.
Define electrolysis.
The splitting of an ionic compound with electricity.
Define electrolyte.
A liquid or substance that conducts electricity.
What do ionic compounds need to be for electrolysis?
Ionic compounds must be molten or dissolved for electrolysis to happen so the electrons can move to carry the electrical charge.
What are the CATHODE and ANODE?
CATHODE = negative electrode where the positive ion is reduced.
ANODE = positive electrode where negative ions are oxidised.
What happens at the cathode during electrolysis? (Reactivity)
Metal formed if less reactive than hydrogen.
Hydrogen formed if more reactive.
What happens at the anode during electrolysis? (Reactivity)
If halide (group 7) ion then it forms.
If not a halide oxygen and water form.
What is the exception to the rules of electrolysis?
If the metal is molten is does not change even if more reactive than hydrogen.
How do you show electrolysis using half equations?
Positive ion before being oxidised = change of electrons goes before arrow. Cu2+ + 2e- = Cu
Negative ion before being reduced = change of electrons goes after arrow. Cu2- = Cu +2e-
Electrons must be balanced
How does electrolysis work?
An electric current is passed through an electrolyte
The positive ions in the electrolyte move toward the cathode to gain electrons and are reduced
The negative ions in the electrolyte move toward the anode and are oxidised, losing electrons.
This creates a flow of charge through the ions so when turned to atoms, they are discharged
How are redox equations constructed?
Cross out the spectator ions (ones that dont change).
Work out what is being oxidised (metal ion) and reduced (ionic compound).
Write out oxidation reaction (including change of state)
Write out reduction reaction (including change of state)
Set it out as a full equation.
How do you conduct an electrolysis experiment?
Place 50cm(cubed) of an electrolyte into a beaker.
Place a Petri dish lid on top and insert two electrodes.
Make sure the electrodes are not touching.
Connect using crocodile clips to a power pack on 4V for 5 minutes.
Observe and record the results.
Test for gases using test tubes and gas tests/litmus paper.
Why is an electrolysis experiment more efficient in a water solution?
Hydrogen (H+) and hydroxide (OH-) ions will be present in the water.
At the cathode both H+ and metal ions are present so if the metal ion is more reactive than hydrogen, hydrogen gas gets produced. If less reactive then metal layer is produced.
At the anode OH- ions and halide ions will be present so halide ions formed if present. If no halide ions are present OH- is discharged and Oxygen is produced.
How is electrolysis of aluminum completed?
The aluminium oxide is initially dissolved in a molten cryolite to lower the melting point.
Aluminum ions receive electrons at the negative electrode and are reduced to aluminium.
Oxide ions lose electrons at the positive electrode and are oxidised to oxygen gas.
The oxygen gas refracts with the carbon graphite electrodes causing damage.
What are the half equations for Aluminum electrolysis?
Aluminum = Al3+ + 3e- = Al
Oxygen = 2O2- = O2 + 4e- (oxygen is diatomic)