Titration

Titration

1. 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)

2. 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

3. IMPORTANT TO BE CARRIED OUT ACCURATELY

4. 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

5. 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

6. acid usually put in burette.... alkali usually in conical flask.... standard volume is 25cm3

   • Phenolphthalein is pink when alkali and colourless when acidic