Making a salt with an alkali

To produce a salt when reacting an acid with an alkali, the method of titration is used. This will produce a soluble salt.

Materials

The apparatus needed includes:

  • a pipette to accurately measure a certain volume of acid or alkali
  • a pipette filler to use the pipette safely
  • a conical flask to contain the liquid from the pipette
  • a burette to add small, measured volumes of one reactant to the other reactant in the conical flask
Apparatus needed for titration: burette, pipette, conical flask and pipette filler.Apparatus needed to carry out a titration

Method

This is an outline method for carrying out a titration in which an acid is added to an alkali.

  1. Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
  2. Add a few drops of indicator and put the conical flask on a white tile.
  3. Fill the burette with acid and note the starting volume.
  4. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
  5. Stop adding the acid when the end-point is reached (the appropriate colour change in the indicator happens). Note the final volume reading.
  6. Repeat steps one to five using the same volume of acid from the burette without using an indicator. The resulting solution can then be evaporated to obtain pure crystals of the salt.

The same method works for adding an alkali to an acid – just swap around the liquids that go into the conical flask and burette.