Anions: Solution
Chemistry 112: Anion Analysis
Page 7
ANION ANALYSIS
M
uch of the work you will be doing in the Chemistry 112 laboratory will be concerned with identifying positive and negative ions, that is, cations and anions, in solutions whose composition is unknown. This procedure is called QUALITATIVE ANALYSIS.
The modern chemist frequently wishes to identify the constituents in a very small amount of substance, and so he depends heavily on instrumental methods of analysis. While the procedures you will use do not use fancy and expensive instruments, your methods are still very effective in determining the major components of systems containing common inorganic ions. Because anion analysis is somewhat simpler than cation analysis, we shall begin our work in qualitative analysis with methods of identifying four common anions in solution:
PO43-, phosphate
Cl-, chloride
SO42-, sulfate
NO3-, nitrate
After having determined the chemical reactions of the individual ions, you will be asked to identify the ions present in an unknown mixture.
CHEMICAL REACTIONS OF INDIVIDUAL ANIONS
1. The BaCl2 Test
Take a set of four small test tubes. After cleaning them, label them 1 through 4, and place 4-5 drops of one of the known solutions in each tube as follows:
Test tube
Known Solution
1
PO43-, phosphate
2
SO42-, sulfate
3
Cl-, chloride
4
Be sure to record the results of your tests in your notebook.
NO3-, nitrate
Next, make each solution slightly basic by adding 5 M ammonia (NH3) dropwise. Making sure the solution is thoroughly mixed, test the basicity of the solution with litmus paper as demonstrated by your instructor.
When the solutions are basic, note any changes that have occurred, and enter your observations in your lab book. Next, add 2-3 drops of 0.2 M BaCl2 to form precipitates between Ba2+ and some of the anions.
Ba2+(aqueous) + anion(aqueous) → [Ba(anion)](solid)
Record observations on the color and
Page 7
ANION ANALYSIS
M
uch of the work you will be doing in the Chemistry 112 laboratory will be concerned with identifying positive and negative ions, that is, cations and anions, in solutions whose composition is unknown. This procedure is called QUALITATIVE ANALYSIS.
The modern chemist frequently wishes to identify the constituents in a very small amount of substance, and so he depends heavily on instrumental methods of analysis. While the procedures you will use do not use fancy and expensive instruments, your methods are still very effective in determining the major components of systems containing common inorganic ions. Because anion analysis is somewhat simpler than cation analysis, we shall begin our work in qualitative analysis with methods of identifying four common anions in solution:
PO43-, phosphate
Cl-, chloride
SO42-, sulfate
NO3-, nitrate
After having determined the chemical reactions of the individual ions, you will be asked to identify the ions present in an unknown mixture.
CHEMICAL REACTIONS OF INDIVIDUAL ANIONS
1. The BaCl2 Test
Take a set of four small test tubes. After cleaning them, label them 1 through 4, and place 4-5 drops of one of the known solutions in each tube as follows:
Test tube
Known Solution
1
PO43-, phosphate
2
SO42-, sulfate
3
Cl-, chloride
4
Be sure to record the results of your tests in your notebook.
NO3-, nitrate
Next, make each solution slightly basic by adding 5 M ammonia (NH3) dropwise. Making sure the solution is thoroughly mixed, test the basicity of the solution with litmus paper as demonstrated by your instructor.
When the solutions are basic, note any changes that have occurred, and enter your observations in your lab book. Next, add 2-3 drops of 0.2 M BaCl2 to form precipitates between Ba2+ and some of the anions.
Ba2+(aqueous) + anion(aqueous) → [Ba(anion)](solid)
Record observations on the color and