Titrations: Technique used to accurately measure the volume of one solution that reacts exactly
with another solution. Used to find concentration of solution, identify unknown chemicals and
find purity of substances.
• Volumetric Flask: They make up standard solutions very accurately due to small neck.
• Preparing Standard Solution:
1- Solid weighed. Solid dissolved in beaker using some distilled water.
2- This solution transferred to volumetric flask. Last traces of solution rinsed into flask with
distilled water.
3- Flask filled to graduation line by adding distilled water a dropwise until bottom of meniscus
lines up at eye level. If too much water added, solution becomes dilute and must be prepared
again.
4- Volumetric flask inverted to mix solution. Or results would be inconsistent.
• Burette: Rinse burette with solution- pour out by slow rotating and tilting. When filling burette,
run excess solution through tap to remove air bubbles.
• Acid- Base Titrations:
1- Add one solution using pipette and indicator to conical flask.
2- Add other solution to burette and record initial burette reading to nearest 0.05cm3
.
3- Run solution in burette into solution in conical flask, swirling conical flask.
4- Eventually indicator changes colour at end point of titration. Record final burette reading. The
volume of solution added from the burette called titre (subtract initial and final burette
reading).
5- Trial titration to find approximate titre (cm3
).
6- Titration then repeated, adding solution dropwise as the end point approached. Repeat
titration until two titrations are concordant within 0.1 cm3.
7- Calculate mean titre from concordant titres. Reject ones not agreeing within 0.1.
• Identification of Carbonate: X2CO3.
– Take measurements of mass of weighting bottle to find mass of X2CO3 solid powder. Prepare
250cm3
solution of unknown carbonate in volumetric flask.
Using pipette measure 25cm3 prepared solution into conical flask. Using burette, titrate this
solution using HCl. Work out mean titre.
– Calculate amount of HCl in moles reacted using CV where V is mean titre used.
– Use molar ratio to work out amount of unknown carbonate reacted in moles.
– Scale up moles by multiplying this mole value to get original solution prepared- divide to get
1cm3 and then x 250 to get 250cm3
.
– Find molar mass in gmol-1 using moles of 250cm3
solution and mass of X2CO3 using Mr moles.
– Use molar mass and take away molar mass of CO3, to leave X2 and use period table to find
unknown element.