Trinity College Dublin, The University of Dublin Titration Demonstration

Trinity College Dublin, The University of Dublin What is a titration? Why do we need it? We need to know the concentration of a solution. It is an analytical technique that allows us to determine the exact concentration of a solution. How does it work? We react our analyte in a controlled way with a solution of known properties.

Trinity College Dublin, The University of Dublin What do we use? Standard solution of KNOWN concentration BURETTE Sample of UNKNOWN concentration Indicator

Trinity College Dublin, The University of Dublin SOLUTION: A solute dissolved in a solvent. SOLUTE: The substance which is dissolved. SOLVENT: The substance in which the solute is dissolved. Aqueous solution: A solution in water. Molarity: Moles of solute per litre of solution. If we know: molarity and litres of solution, we can calculate moles (and mass) of solute. …REMINDER… 

Trinity College Dublin, The University of Dublin The Experiment : What do I need? Standard solution of NaOH of KNOWN concentration BURETTE Indicator Titration of HCl with 0.1M NaOH NaOH + HCl  H 2 O + NaCl 25 mL of HCl of UNKNOWN concentration 

Trinity College Dublin, The University of Dublin Sample of UNKNOWN concentration : HCl …but known volume to transfer an exact amount of sample solution we need to use a pipette

Trinity College Dublin, The University of Dublin Process of using the pipette Pipette is placed in volumetric flask and filled to calibration mark then emptied into clean conical flask Pipette filler is attached to top of pipette

Trinity College Dublin, The University of Dublin Standard solution of KNOWN concentration : NaOH We need exact MASS And exact VOLUME

Trinity College Dublin, The University of Dublin Making up a standard solution 3.Solution is then transferred to volumetric flask to make sure that the volume of the solvent is exact. 1.Weigh out solid on balance 2.Dissolve solid in water and stir with a glass rod

Trinity College Dublin, The University of Dublin Add distilled water to about 1cm below the mark on the volumetric flask. Use a Pasteur pipette to add water dropwise to the mark. Remember to stopper the flask and shake well to mix

Trinity College Dublin, The University of Dublin Take note of the starting volume in the burette. Read the volume from the bottom of the meniscus

Trinity College Dublin, The University of Dublin Dispensers are used in the lab and the volume you require will have been set up on the dial for you. NOTE: To prepare solutions of a lower concentration (e.g. from conc. HCl) you need to dilute it correctly.

Trinity College Dublin, The University of Dublin Burette is rinsed with the standard solution (e.g. NaOH) and then filled avoiding the formation of bubbles near the tap Burette

Trinity College Dublin, The University of Dublin Set up for Titration Burette of standard solution is placed in clamp over conical flask with the sample. 1-2 drops of phenolphthalein indicator is added to the 25mL of sample in the conical flask. White paper beneath flask helps visualise the colour change.

Trinity College Dublin, The University of Dublin Slowly add solution to the flask from burette while gently swirling. After some time, a pink colour will appear and quickly disappear as the solutions are mixed. The longer the pink colour persists, the closer to the end-point (stoichiometric point). When you get close to the end add drop by drop until the full solution is pink. RECORD THE VOLUME OF SOLUTION USED FROM YOUR BURETTE Use the first result as an indication then repeat the analysis until the results are within 0.1mL of each other.

Trinity College Dublin, The University of Dublin An Indicator is used to signal the end-point. It is a highly coloured dye which shows a very sharp colour change at a specific pH. End-point indicates that a reaction is complete. Incomplete End-point overshoot How to find the end-point

Trinity College Dublin, The University of Dublin

Trinity College Dublin, The University of Dublin Titration of HCl with 0.1M NaOH

Trinity College Dublin, The University of Dublin VOLUMETRIC ANALYSIS