Chemical Changes Flashcards
What happens to a substance in terms of oxygen during oxidation and reduction
Oxidation a substance gains oxygen
magnesium + oxygen —> magnesium oxide
-magnesium gains oxygen so its oxidised
Reduction a substance looses oxygen
lead oxide + carbon —> lead + carbon dioxide
-lead looses oxygen so is reduced
What are the elements above carbon in the reactivity series starting from most reactive
potassium, sodium, calcium, magnesium, aluminium
what are the elements below carbon in the reactivity series
zinc, iron, tin, lead, hydrogen, copper, silver, gold, platiunum
what is a displacement reaction
-example
-when a more reactive metal displaces a less reactive metal from a solution of its salts
magnesium + copper sulfate —> copper + magnesium sulfate
how can elements less reactive than carbon be extracted from metal oxides (ores)
heating with carbon
iron oxide + carbon —> iron + carbon dioxide
-iron looses oxygen so is reduced
-carbon gain oxygen so is oxidised
describe oxidation and reduction in terms of electrons
-example with magnesium and oxygen
oxidation is loss of electrons
2Mg —> 2Mg2+ + 4e-
reduction is gain of electrons
O2 + 4e- —> 202-
what pH numbers make a solution
- neutral
- acidi
- alkaline
pH 7 is neutral (green)
pH less than 7 are acidic (red)
pH more than 7 are alkaline (purple)
what does an acid produce when it is neutralised with a base
acid + metal hydroxide —> salt + water
what ions do acids and alkalis contain and how are they neutralised
Acids contain hydrogen ions H+
Alkalis contain hydroxide ions OH-
H+ + OH- —> H20
neutralised by reacting them together as they have a pH of 7 and produce water
What is produced when an acid reacts with metal oxides and metal carbonates
acid + metal oxide —> salt + water
acid + metal carbonate —> salt + water + carbon dioxide
How is a salt produced and what ones are produced for hydrochloric acid, nitric acid and sulphuric acid
a salt is produced when the hydrogen in the acid is replaced by the metal ion
hydrochloric acid produces chloride salts
nitric acid produces nitrate salts
sulphuric acid produces sulphate salts
what makes an acid strong or weak
strong acid are completely ionised (split up into ions) in water
Hydrochloric acid
HCL + aq —> H+ Cl-
weak acids only partially ionise in water
Ethanoic acid
CH3COOH + aq —> CH3COO- + H+
why do ionic compounds only conduct electricity when in solution or molten
the ions are free to move and carry their charge
what happens to the positively charged metal ion during electrolysis
what happens to the negatively charged ion during electrolysis
the positive metal ions move to the negative cathode and gain electrons to form pure metal
Pb2+ + 2e- —> Pb
the negative ions move to the positive anode and loose electrons to from a molecules (bromine) and release gas
2Br- —> Br2 + 2e-
where to oxidation and reduction occur during electrolysis
-half equations for copper chloride
oxidation occurs at the positive electrode where the negatively charged ions loose electrons
2Cl- —> CL2 + 2e-
reduction occurs at the negative electrode where positively charged ions gain electrons
Cu2+ + 2e- —> Cu
