chemical changes 4 Flashcards
what is the PH scale
a measure of how acidic or alkaline a solution is
the lower the PH the more acidic
the higher the more alkaline
what is indicator
a dye that changes colour depending on weather it’s above or below a certain PH
some indicators contain a mixture of dys that means they gradually change colour over a broad range of PH
ways to measure PH
PH probe
measure electronically
what is an acid
a susbstance that forms aqueous solutions with PH of less than 7
Acids form H plus ions
what is a base
a substance with a PH level greater than 7
Base(alkali)
base that dissolves in water to form a solution with PH greater than 7
form OH minus ions
acid + base =
salt + water
H plus + OH minus =
H2O
what do reactions of strong acids and alkali help calculate
reactions of a strong acids and alkalis to calculate the concentration by titration
what PH does a neutral substance have
PH 7
what do strong acids do in water
ionise completely in water
all acid particles dissociate to release H plus ions
what do weak acids do in water
do not fully ionise
only a small proportion of particles dissociate to reales H plus ions
what kind of reaction is a weak acid
reversible reaction which sets up an equillibrium between the undissociated and dissociated ions.
lies on the left because only few H plus ions are released
what happens when the concentration of H plus ions increase
rate of reaction will be faster if strong acid
what is the PH of acid or alkali and what happens when the scale decreases
a measure of the concentration of H plus ions
for every decrease of 1 on the PH scale the concentration increases by a factor of 10
general rule when ion concentration changes
factor h plus ion concentration changes by 10-x (x is difference in PH)
what does acid strength tell you
what proportion of the acid molecules ionise in water
what is acid concentration
how much acid there is in a certain volume