Remember that when using such small amounts, it is extremely important that the equipment that you use is very clean. If the equipment is “dirty,” the solutions will become contaminated, and it is possible that you will identify the contaminant rather than the unknown. To avoid cross contamination, make sure to recap reagent bottles with the original caps and to clean your droppers very well if they are to be reused. The flame test is fast and easy but requires some practice to reliably produce and see the colors (some ions will be more intensely colored than others).
To carry out a flame test, you will use a clean inert wire and a clean watch-glass with a few drops of the aqueous solution. Clean a piece of nichrome wire (or paper clip) by first heating the wire in a hot Bunsen burner flame until it glows red hot. Dip the wire into a nitric acid (or hydrochloric acid) solution (see safety note in margin area), heat again, and then rinse with distilled water. Repeat these steps until the wire burns without color. To test an unknown, place some unknown. olution onto a watch glass and hold it next to the air inlet at the bottom of your Bunsen burner. Heat the wire in the flame and then plunge the hot wire into the solution in the watch glass.
This will vaporize the solution, allowing it to be carried with the air into the flame producing a colored flame. Testing salts for anions nd cations Introduction Chemists often have to identify the composition of unknown substances. This experiment involves identifying the cations and anions in various salt solutions. What to record Sample Test performed Result of test What to do
- Dissolve the unknown substance in deionised water. 5–10 cm 3 of solution may be needed.
- Using the analysis table, test small aliquots (portions).
- Repeat for the other unknown substances. Safety Wear eye protection. Some of the unknowns may be toxic or corrosive.
