acids, alkalis and titrations Flashcards
litmus is from
lichens
synthetic indicators used in acid-alkali titrations
phenolphthalein and methyl orange
litmus colour in acid and alkali
acid-red
alkali- blue
phenolphthalein colour in acid and alkali
acid- colourless
alkali- pink
methyl orange colour in acid and alkali
acid-red
alkali- yellow
synthetic indicators are used to
show the endpoint in titrations as they have a very sharp colour change when an acid has been neutralised by an alkali and vice versa
litmus isn’t suitable for titrations because
as the colour change is not sharp and it goes through a purple transition colour in neutral solutions making it difficult to determine an endpoint
litmus is very helpful as a
indicator paper because it comes in red or blue versions, for dipping into solutions or testing gases
the ph scale goes from
0-14 (very acidic substances have values below 0)
all acids have a pH of
below 7
all alkalis have a pH of
above 7
the lower the pH is
the more acidic the solution is
the higher the pH is
the more alkaline the solution is
a solution of 7 is
neutral
universal indicator is a
wide range indicator and can give only an approximate value for pH
universal indicator is made of
a mixture different plant indicators which operate across a broad pH range and is useful for estimating pH of an unknown solution
how does a universal indicator work
a few drops are added to the solution and the colour is matched with a colour chart which indicates the pH which matches with specific colours
when acids are added to water
they form positively charged hydrogen ions (H^+)
the presence of H^+ ions is
what makes a solution acidic
when alkalis are added to water
they form negative hydroxide ions OH^-
the presence of the OH^- ions is
what makes the aqueous solution an alkali
the pH scale is a
numerical scale which is used to show how acidic for alkaline a solution is, so to measure the amount of ions present in a solution
a neutralisation reaction occurs when
an acid reacts with an alkali
when substances react together in a neutralisation reaction
the H^+ ions react with the OH^- ions to produce water
the net ionic equation of all acid-base neutralisations is
H^+ + OH^- -> H2O
