Acids and Alkalis Flashcards
PH
a measure of how alkaline or acidic a substance is
0-14
low numbers = acid, high numbers = alkaline
ways of measuring pH
Universal indicator
ph probe with meter
phenolphalien
methyl orange
base
any substance with a PH greater than 7
alkali
subgroup of bases that are soluble in water
forms OH- ions in water
acid
any substance that forms an aqueous solution with a PH less than 7
forms H+ ions in water
common acids
Hcl (hydrochloric acid)
H2SO4 (sulfuric acid)
HNO3 (nitric acid)
titration
a technique where a solution of known concentration is used to determine the concentration of an unknown solution
general equations for a neutralision reaction
metal oxide + acid –> salt + water (this is for an acid)
metal hydroxide + acid –> salt + water
ionic equation for neutralisation reaction
e.g. H+ + OH- –> H2O
e.g. HCl + NaOH –> NaCl + H2O
if a substance is neutral, it will have a PH of 7
ionic equation definition
reaction involving ions in a solution
anything that is made up of ions and is aqueous will break up into its ions in a solution
spectator ions
ions that do not contribute in the equation
how titration works
use a pipette and add some acid to a flask.
add a small amount of phenolphthalein indicator.
fill the burette with base and carefully drop some into the acid
when the colour changes, stop and record the volume
repeat several times and get an average.
how can you make the titration test easier
we can add acid to the base slowly and take readings on a PH probe (gives exact PH values)
we can plot a graph against volume of acid added
how can you make the titration test easier
we can add acid to the base slowly and take readings on a PH probe (gives exact PH values)
we can plot a graph against the volume of acid added
equivalence point
point in titration at which the volume of acid added is just enough to neutralize the solution
strong acids
dissociate completely
PH of 0-2
can have low concentrations
weak acid
dissociate partially
PH of 3-6
can have high concentrations
examples of weak acids
ethnoic acid, citric acid
acid concentration
the mass of acid dissolved in a given volume of water
changing the concentration of an acid affects its PH
equation for concentration
concentration = mass/volume
dont confuse strength of an acid with concentration
just dont
if an acid with a PH of 6 changes to a PH of 3, how much did the concentration change?
the H+ concentration has increased by a factor of 1000
if an acid with a PH of 6 changes to a PH of 9, how much did the concentration change?
the H+ concentration has decreased by a factor of 1000
other general equations that you have to know for the test
acid + metal –> salt + hydrogen
acid + metal carbonate –> salt + water + carbon dioxide
all polyatomic ions to know
CO3^2-
Cl-
NO3-
SO4^2-
precipitation reaction
adding two soluble salts together to make insoluble salts
soluble or insoluble:
salts of Na, K and NH4
nitrates
common chlorides
common sulphates
common carbonates and hydroxides
soluble or insoluble:
soluble
soluble
soluble except silver and lead
soluble except lead, barium and calcium
insoluble except sodium, potassium and ammonium
Acid strength
The amount of acid that dissociated (what portion of acid molecules ionised in water)
colour of methyl orange in acid
red
colour of methyl orange in alkali
yellow
colour of phenolphelien in acid
colourless
colour of phenolphthalein in alkali
pink
explain the steps in a soluble salt from insoluble base experiment
pour a dilute acid into a flask
heat flask
add base, e.g. copper oxide into the flask
heat speeds up the rate of reaction
repeat last step until base stops reacting with acid
this is done to ensure the mixture has reacted completely
leave to cool
filter mixture into a beaker and pour into an evaporating basin
place evap basin on top of a beaker with water, the beaker with water will evaporate which will in turn heat the evap basin
heat until small amount of mixture in the evap basin is left
this is done as too much evaporation would leave behind a powder. we want salt crystals
leave to cool, soon after, crystals will form
