Chemical changes - Acids, alkalis and reactivity Flashcards
acid + base –
salt + water
what is an acid
a substance that forms a H+ ions when dissolved in water
what is a base
a substance that can neutralise an acid, producing a salt + water
what is an alkali
a base that are soluble and that produce OH- ions when dissolved in water
what is the reaction between a base and an acid called
neutralisation
what is a strong acid
an acid that ionises completely in water into it’s H+ ions
what is a weak acid
an acid that does not fully ionise in a solution, only a small proportion of acid particles dissociate to release H+ ions
examples of strong acids
sulfuric, hydrochloric, nitric acids
examples of weak acids
ethanoic, citric, carbonic acids
what is the difference between strong and concentrated acids
acid strength tells you what proportion of the acid molecules ionise in water, whilst the concentration measures how much acid there is in a certain volume of water
what does an acid + metal oxide give
salt + water
what does an acid + metal hydroxide give
salt + water
what does an acid + metal carbonate give
salt + water + carbon dioxide
what does acid + metal give
salt + hydrogen
examples of metals that do not react with water but react with dilute acids
magnesium, aluminium, zinc, iron and lead (iron and lead react slowly).
metal + water
metal hydroxide + hydrogen
how to separate metals in terms of reactivity
- see how they react with water
- potassium, sodium and lithium react very rapidly with water at room temperature
- calcium reacts quite rapidly
- magnesium, zinc, iron and copper do not react with water at room temperature
why cant we react group 1 metals with dilute acids
because they would have a dangerously fast reaction with them
how do certain metals react with dilute acids
calcium- extreme vigorous reaction magnesium - rapid reaction
zinc - quite rapid but slower but magnesium
iron - quite slow reaction
copper - no reaction
what does the reactivity of a metal depend on
its ability to lose electrons and form a positive ion
where are unreactive metals such as gold found
in the earth as a metal itself
why is carbon used to displace elements from their compound
because metals higher in the reactivity series are more expensive and carbons cheappp
describe a neutralisation reaction between an acid and an alkali
- acids produce H+ ion
- alkalis produce the OH- ion
- when they react, the hydrogen ions react with the hydroxide ions to produce water
H+ + OH- —-> H2O
what do salts contain
- positive ion from the base or the alkali
- a negative ion which comes from the acid
if an acid is weak, what direction does the arrow in the reaction go
both ways, its a reversible reaction
what the relationship between pH and acid strength
stronger acids have a lower pH than weak acids for a given concentration
- thats because strong acids fully ionise, producing a greater concentration of hydrogen ions than weaker acids
as the pH scale decreases by one unit, how much does the concentration of hydrogen ions decrease by
10 times (one order of magnitude)
what does the concentration of an acid tell us
the amount of acid molecules in a given volume of solution
what is a dilute acid
one that has fewer acid molecules in a given volume
