Topic 4 (Chemical Changes) Flashcards
PH Scale goes from
0 to 14
0 on the PH scale is
Acidic
14 on the PH scale is
Alkaline
How can you measure ph
•PH probe
•Indicator
What do acids and bases do
Acids and bases neutralise each other.
An acid is a substance with a PH less than 7 and they form H+ ions. An alkali is a base that dissolves in water to form a solution with a PH more than 7 and they form OH- ions. (H+)+(OH-)->H2O
Acid + Base ->
Salt + Water
What do titrations do
They find out concentration
How do you find unknown concentration using titrations
Add a set volume of either alkali to a flask. Add two or three drops of an indicator e.g phenophalene. Fill a burette with an acid with known concentration. Use the burette to add acid to the alkali 1cm^3 at a time giving the flask a regular swirl. When the indicator changes colour stop and see how much acid was required to neutralise the alkali. Then work out concentration of alkali.
What is a strong acid
An acid that completely ionises into water
What is a weak acid
An acid that only partially ionises in water
What is concentration of an acid
How watered down the acid is. You can have a dilute strong acid or a concentrated weak acid they have no correlation.
Metal oxides and metal hydroxides are bases what do they form when reacting with an acid
Metal Oxide/Hydroxide+ Acid
-> Salt and Water
When a metal carbonate reacts with an acid it produces CO2
Metal Carbonate + Acid
-> Salt+Water+CO2
What is the reactivity series
Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper
What happens when metals react with acids
Metal + Acid
-> Salt + Hydrogen
What is oxidation
The gain of oxygen
What is reduction
Loss of oxygen
What is oxidation in terms of electrons
Loss of electrons
What is reduction in terms of electrons
Gaining electrons
What is electrolysis
Splitting up a compound with electricity
How does electrolysis work
During electrolysis an electric current passes through an electrolyte. The ions on the electrolyte move towards the electrodes and the compound decomposes. When the ions reach the electrodes they gain or lose electrons to form uncharged atoms and are discharged from the electrodes.
Why are some metals extracted using electrolysis
If a metal is too reactive to be displaced by carbon, electrolysis is used to extract it
In an aqueous solution as well as the ions from the compound what other ions will be present
H+
OH-
Both from the water
In electrolysis of an aqueous solution what goes to the cathode
Whatever element is less reactive, this usually means hydrogen
