Investigation 5 Flame Tests

『Aim』

Know the unknown solution by use flame test based on its characteristic color.

『Safety』

Wear safety goggles and follow the standard safety procedure as outlined. Don’t touch the end of the wire loop used in the flame tests. This wire gets extremely hot and can cause severe burns.

『Background』

Each of the cation in different salt solutions，will make different flame color. The flame test is a qualitative test used in chemistry to help determine the identity or possible identity of a metal salt based on the characteristic color the salt turns the flame of a Bunsen burner or metalloid ion found in an ionic compound. If the compound is placed in the flame of a gas burner, there may be a characteristic color given off that is visible to the naked eye.

『Materials』

6 test tubes 50ml beaker 0.1M LiCl

Test tube rack Nichrome (Ni-Cr) wire 0.1M NaCl

Droppers ...

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『Materials』

6 test tubes 50ml beaker 0.1M LiCl

Test tube rack Nichrome (Ni-Cr) wire 0.1M NaCl

Droppers Tongs 0.1M CaCl2

Bunsen burner 6M HCl 0.1M BaCl2

0.1M KCl Unknown solution

『Method』

Each of 5 test tubes with the name of a salt solution was labeled; then the sixth tube unknown was labeled. 1ml of each salt solution was added to the appropriately labeled test tube.
One end of the nichrome wire was grasped with the tongs. The wire was cleaned by alternately heating it in the hot burner flame and dipping it into the hydrochloric acid. This procedure was repeated for several times until the flame remains almost colorless when the wire was heated.
The clean wire was dipped into the sodium chloride solution and then was held it in the hot burner flame. The color of the flame was recorded and step 2 was repeated to clean the wire.
Step 3 was repeated for each of the remaining salt solutions. A flame test was performed with the unknown solution. The color of the flame was noted and unknown substance was identified.

『Data Collection』

『Processing』

We need use purple filter to see KCl and unknown solution.

『Conclusion and evaluation』

From the data collection we can know that: Li compound has red color, Na compound has yellow color, Ca compound has brick red color, Cu compound has green color, Ba compound has yellow color and the unknown substance has K+ cation.

We should let Bunsen burner’s flame near colorless.

Nichrome (Ni-Cr) wire should wash cleanlily, or it will influence next solution’s flame color.