3.4.5 Making soluble salts Flashcards
1
Q
How to make soluble salts?
A
By neutralising acid and crystallising the resulting solution.
2
Q
How to make soluble salt crystals using an insoluble base?
A
- Add excess base to hot acid. Hot acid has more energy so it will react faster with the base.
- Filter out the excess base. The salt solution is the filtrate and is collected in an evaporating basin.
- Heat the salt solution until the crystals start to form around the edges. This saturates the solution so that crystals form more efficiently.
- Leave the salt solution to crystallise. Evaporation of water allows crystals to form.
- Dry the crystals by dabbing them with a paper towel.
3
Q
How to make soluble salts using a soluble base?
A
- Do a titration to measure the volumes of acid and alkali that neutralise each other:
- Use a volumetric pipette to measure out 25cm cubed of an alkali into a conical flask.
- Add a few drops of phenolphthalein indicator to the flask. Universal indicator doesn’t work because it changes colour too gradually.
- Fill a burette with an acid and clamp it above the conical flask.
- Measure the initial volume of the acid on the burette to the nearest 0.05cm cubed.
- Use the burette to add the acid into the conical flask, one drop at a time. Swirl the flask as you add each drop.
- Close the burette tap as soon as the colour in the conical flask changes.
- The start colour will be pink and the end colour will be colourless.
- Measure the final volume of known acid on the burette, to the nearest 0.5cm cubed.
- Calculate titre (final volume - initial volume). - Repeat the titration, but this times don’t put the indicator in. Use the burette to add exactly the right volume for neutralisation.
- Heat the salt solution until the crystals start to form around the edges. This saturates the solution so that crystals form more efficiently.
- Leave the salt solution to crystallise. Evaporation of water allows crystals to form.
- Dry the crystals by dabbing them with a paper towel.
