Wednesday, 20 May 2015

Titration to determine volume of acid needed to neutralise an alkali

Equipment

Burette with clamp and stand
Pipette (10ml) with filler bulb
Conical Flask
Funnel
Known concentration (1 molar) Hydrochloric Acid
Unknown concentration alkali solution
Phenolphthalein Indicator
Deionised water

Method

Use the pipette to measure 10ml of alkali solution into the conical flask. Add 5 drops of the indicator to turn the solution pink.

Fill the burette with acid using the funnel, ensuring the tap is closed before starting to fill. Allow some acid to run through to ensure there are no air bubbles in the nozzle. Ensure the the burette is starting at the 0ml mark.

Add the acid to the conical flask 5ml at a time, swirling between each addition to find the rough end point of the reaction (when the solution in the flask goes clear).

Refill the burette, rinse out the conical flask with deionised water and put another 10ml of alkali in there.

Add acid from the burette until you are approximately 5ml from the endpoint, then continue to add acid, but at a much slower rate. Ideally you will add one final drop which will neutralise the solution.

Once you have recorded the volume of acid required repeat twice more.

Risks

Glassware can break if not handled correctly so care should be taken and if anything does break a dustpan and brush should be used to sweep up all the pieces. Acid and alkali can be irritant or worse so goggles should always be worn, care should especially be taken when filling the burette.