1) Add a known volume of alkali into a conical flask using a pipette
2) Add a few drops of indicator ( Phenolphthalein / Methyl orange)
3) Pour some acid into a burette, and record the reading (meniscus)
4) Open the tap ,add a small amount of acid and swirl the conical flask to mix
5) add acid until the solution is neutral as shown by the colour chnage in the indicator
6) Repeat (3 times)
may be used to determin the volumes of acid
and alkali needed to mwke a neutral salt solution
OR to determine the conentration of an acid or
alkali , if the concentration of the other react is
known
IMPORTANT TO BE CARRIED OUT ACCURATELY
MENISCUS -- curve in the surface of a liquid
The burette and pipette used in
accurte titrations must be read from
the bottom of the
meniscus.......precision of burette
reading is +/- 0.05 cm3
Calculations
concentration in g/dm3 = mass in g / volume in dm3
concentration in g/dm3 = amount in moles / volume in dm3
eg 40g in 500 cm3 what is the concentraion in moles /dm3
500/1000 = 0.5........40 / 0.5 = 80 so it is 2moles/dm3
to convert volume from cm to dm divide by 1000 and vice versa
concentration of a solution can be measured in moles per dm3
acid = alkali (concentration x volume)
eg ... a titration is done where 25.0 cm3 of acid is placed into a conical
flask. the concentration of the acid is not known. The acid was
neutralised with 13.5 cm3 of sodium hydroxide of concentraion of
0.10moles/dm3. calculate the concentraion in moles/dm3 of acid.
assume that 1 mole of sodium hydroxide reacts completely with 1 mole
of acid
?x25 = 0.1 x 13.5 --- 1.35
1.35 / 25 = 0.054 mol/dm3
acid usually put in burette.... alkali usually in conical flask.... standard volume is 25cm3
Phenolphthalein is pink when alkali and colourless when acidic