acids, bases and salts Flashcards
what is an acidic solution
a solution with pH less than 7
the lower the pH the stronger the acid
what is an alkaline solution
A solution with a pH more than 7
the higher the pH, the stronger the alkali
an alkali is a base dissolved in water
what is the pH of a neutral solution
pH 7
what ions do acids contain
hydrogen ions, H+
what do alkalis contain
hydroxide ions, OH-
what is a strong acid
an acid which completely dissociates to release H+ ions in an aqueous solution
what is a weak acid
an acid which partially dissociates to release h+ ions in a aqueous solution
what is a strong base
A base which completely dissociates to release OH- (hydroxide) ions in an aqueous solution
what is a weak base
a base which partially dissociates to release OH- ions in an aqueous solution
what is the product formed when a metal is added to a dilute acid
acid + metal –> salt + hydrogen
generally the more reactive the metal in the reactivity series, the faster the reaction
what are the three neutralisation reactions of dilute acids
acid + alkali –> salt + water
acid + base –> salt + water
acid + metal carbonate –> salt + water + carbon dioxide
the composition of salt formed depends on the acid used and the positive ions in the base, akali or carbonate
what is neutralisation
the reaction of hydrogen ions with hydroxide ions to form water
hydrogen + hydroxide –> water
H+ + OH- –> H2O
how can you test for the presence of carbonates
carbonates react with dilute acids to form carbon acids
the gas formed from this reaction can be bubbles through lime water; if limewater turns cloudy, the gas is CO2
how to prepare salt from a metal or insoluble base / carbonate
STEP 1
excess metal / base / carbonate is added to the acid to make sure all the acid has reacted and been used up
heating and stirring help the process
for metals and metal carbonates the fizzing stops when all the acid has been used up
STEP 2
the mixture is filtered using a filter funnel and filter paper
the excess solids remains in the filter paper. the salt solution passes through into the evaporating basin
STEP 3
the salt crystals are collected from the solution by evaporation
large crystals - evaporate water slowly near a radiator or window ledge
small crystals - use a bunsen to evaporate 2/3 of water quickly, before allowing to crystalise naturally
what are the names of the salts formed from:
hydrochloric acid
nitric acid
sulfuric acid
hydrochloric acid produces chlorides
nitric acid produces nitrates
sulfuric acid produces sulfates
what is the test for sulfate ions
first add dilute hydrochloric acid, followed by barium chloride solution
a white precipitate will form if sulfate ions are present in the solution
what is titration used for
a method to prepare solutions of soluble salts
to determine the relative and actual concentrations of solutions of acids/alkalis
how do you calculate the concentration of a solution
concentration = mol ÷ volume
the units of concentration are mol dm-3
what does the concentration of an acid / base refer to
the amount of substance present - the number of moles of acid/base in a solution
what does the strength of an acid / base refer to
the strength refers to the degree of ionisation of the acid or base - how readily the acid releases hydrogen (H+) ions or how readily the base releases hydroxide (OH-) ions
outline how to perform a titration
measure exactly 25cm3 of alkali into a clean conical flask
add a few drops of indicator (2-3) to the flask
place the flask onto a white tile
fill the burette with acid
slowly add the acid from the burette to the alkali until the indicator changes colour
this is the end point of the reaction
record the volume of acid added to the flask
repeat steps 1-6 without using the indicator and addin the same volume of acid from the burette
the salt crystals are collected from the solution by evaporation
what is a precipitate
two solutions containing salts combining together to form an insoluble salt
how are insoluble salts prepared
mixing - the two soluble salt solutions are mixed
filtration - the insoluble precipitate is separated from the mixture by filtration. the precipitate is separated from the mixture by filtration. the precipitate stays behind in the filter paper, while the solution passes through
washing and drying - water can not dissolve the precipitate - it is insoluble - but it can wash of any remaining impurities. the filter paper is then removed, opened out the precipitate is dried in a oven
