Volumetric analysis of vinegar

Equipment list.
- Burette and stand
- 20.0 mL and 25 mL pipettes and filling bulb
- white tile
- phenophthalein (indicator)
- 3 X 100 mL conical flasks
- 250 mL volumetric flask
- funnel
- vinegar sample
- 0.10M NaOH

Look at the video on the right.

What is a burette used for?

To how many decimal places is the burette reading? 2 3 4 1

The meniscus is the curved surface of the water. We read the burette from the middle of the meniscus bottom of the meniscus top of the meniscus

What indicates the end point of titration? the flask is full the indicator changes colour pemanently the burette is empty the solution changes colour for a short while

Consumers are happy paying more for the same product as long as they feel good. Advertising makes consumers feel better buying a ceratin product. But this comes at a cost. Compare two brands of vinegar for example. Skipping Girl is a very popular brand of vinegar while Home Brand is a generic brand less than half the price.

Two litres of Home Brand vinegar costs $1.30 while two litres of Skipping Girl costs $3.56. The active ingredient in vinegar is acetic acid. We can measure how much of this acid is in each brand of vinegar.

We react the acetic acid with a base, sodium hydroxide. We measure very accurately how much base we add to a specified volume of each brand of vinegar. This gives us a very good indication of how much acid is present.

Often we may have to dilute the vinegar as it is too concentrated for our investigation.

Step 1 Use a pipette to deliver 20.0 mLof the diluted vinegar sample into a conical flask. Your teacher will show you how.

Step 2 Add two drops of indicator.

Repeat the 4 steps as many times as required to get three concordant results. Then average out the three.

Concordant results are results where the highest and the lowest differ by less than 0.1ml.

Why do you think Skipping Girl is more expensive than Home Brand? Is the cost justified?