Testing for sulfates: barium chloride gives a white precipitate
Definition
Sulfate ion
A negatively charged group of atoms with the formula SO42−\text{SO}_4^{2-}SO42−, found in sulfate salts.
Definition
Precipitate
A precipitate is an insoluble solid that forms when substances in solution react.
- A sulfate contains the sulfate ion, SO42−\text{SO}_4^{2-}SO42−.
- Add a few drops of dilute hydrochloric acid, then barium chloride solution.
- A white precipitate of barium sulfate forms if a sulfate is present.
Practical
Identifying a sulfate
- Put about 1 cm1\,\text{cm}1cm depth of the solution into a test tube.
- Add a few drops of dilute hydrochloric acid.
- Add barium chloride solution.
- A white precipitate confirms that the sample is a sulfate.
Why the acid, and the ionic equation (higher tier)
- The dilute hydrochloric acid removes carbonate ions, which would also form a white precipitate and give a false result.
- The ionic equation is Ba2+(aq)+SO42−(aq)→BaSO4(s)\text{Ba}^{2+}(aq) + \text{SO}_4^{2-}(aq) \rightarrow \text{BaSO}_4(s)Ba2+(aq)+SO42−(aq)→BaSO4(s).
- Barium sulfate is insoluble, which is why it appears as a white solid.
Self review
- Which ion does a sulfate contain?
- Which two reagents are used to test for a sulfate?
- What is the positive result for a sulfate?
- Write the ionic equation for the formation of barium sulfate.
