Chemistry Quantitative Analysis

Unit 4 – scientific practical techniques

Quantitative analysis (part A) & qualitative analysis (part B)

TASK 1

(i) Sodium hydroxide/hydrochloric acid titration using phenolphthalein as an indicator.

Equipment

* Small filter funnel

* 1 x 50cm3 burette

* Boss head

* Clamp

* Stand

* 1 x 25cm3 bulb pipette and filler

* 1 x white tile

* 250ml conical flask

* 100 ml 0.5M sodium hydroxide

* Phenolphthalein

* 100ml 0.5M hydrochloric acid

Method

1. Make sure that the tap of the burette is closed and add a small amount of hydrochloric acid (approximately 10 cm3) through using a funnel. Remove the funnel and putting your thumb over the top spread the acid up the burette taking care not to get any on your hands, then pour the acid away

2. Then clamp the burette onto the retort stand upright, using the funnel, fill it with hydrochloric acid to just a bit past the 0cm3 mark. Place a small beaker under the burette and open the tap to just a slow drip letting the acid level drop to 0cm3 and close the tap. Pour the acid in the beaker away.

3. Using a 25cm3 bulb pipette (clean), put 25cm3 of sodium hydroxide into a clean conical flask placing the flask on a white tile.

4. Add a few drops of phenolphthalein indicator and record the colour.

5. Open the tap on the burette to let 15cm3 of acid into the flask, swirl the flask as you are adding the acid. Then partially close the tap to allow slow drips ( 1cm3 portions) swirling after each drop.

When the end point gets closer you should be able to see the colour change from clear to pink at the point where the acid is entering the liquid. When the solution is swirled the pink will disappear but eventually the pink colour will stay for longer periods until eventually the pink colour stays permanently. At this point you should stop the flow and read the burette to see how much acid you have added and record the results as followed

Experiment no. | Initial burette reading | Final...