Experiment 4
Title = Qualitative Analysis of Anions
Objectives
• Part 1: Test for the presence of the anions in a solution
PO43- (phosphate), SO42- (sulfate), and Cl- (chloride).
Background: molecular , complete ionic & net
ionic equation
• The molecular equation shows each of the substances in the reaction
as compounds with physical states written next to the chemical
formulas
• a complete ionic equation also includes the spectator ions
• A net ionic equation shows only the chemical species that are involved
in a reaction,
Background: molecular , complete ionic &
net ionic equation
For example: The reaction of potassium chloride (KCl) and lead II nitrate Pb(NO3)2
Molecular Equation: 2KCl (aq) + Pb(NO3)2 (aq)
2KNO3 (aq) + PbCl2 (s)
Complete Ionic Equation: 2K+ (aq) + 2Cl- (aq) + Pb2+ (aq) + 2NO3– (aq)
PbCl2 (s)
Net Ionic Equation: 2Cl- (aq) + Pb2+ (aq)
PbCl2 (s)
(precipitation reaction)
2K+ (aq) + 2NO3– (aq) +
Procedure
1.
2.
3.
4.
Next, make each solution slightly basic by adding 5 M ammonia
(NH3 or NH4OH) 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 notebook. Next, add 2-3
drops of 0.2 M BaCl2 to form precipitates between Ba2+ and some
of the anions.
Record observations on the color and appearance of the
precipitate(s) in your notebook. It is best to draw a table in your
notebook like the one below
1. Test with BaCl2
A) Testing for sulfate ion (Sulphate | SO42-) in Qualitative Analysis
Testing for Sulfate ion with aqueous barium chloride solution
Add aqueous barium chloride (BaCl2) solution to the sulfate ion solution
and observe the differences. Barium sulfate (BaSO4), is a white
precipitate. BaSO4 is not soluble in strong acids and dilute acids
Chemical reaction:
Experiment 4
• Test 1: reaction with Ba2+
• 1) Ba2+ + PO43- Barium phosphate
• 2) Ba2+ + SO42- Barium sulfate (s)
• 3) Ba 2+ + Cl- Barium Chloride
Precipitation Reactions
Record observations on the color and appearance of the
precipitate(s) in your notebook
Example 1: Test for the presence of sulfate ion, SO42observation:
A white precipitate indicates the presence of the SO42 ion.
Chemical reaction
Molecular: BaCl2 (aq) + Na2SO4 (aq)
2 NaCl (aq) + BaSO4(s)
Complete ionic:
Net ionic:
Observation: Barium sulfate BaSO4: white precipitate, insoluble in water.
Results
B. Test for the presence of phosphate ion, PO43-
C. Test for the presence of chloride ion, Cl-
In Qualitative analysis for chloride ion, colors, solubility, precipitates of chloride
compounds are important and we are learn different experiments to test the presence of
chloride ion.
Do the test with BaCl2:
Are there any reaction?
Observation
you may use this table to summarize your
observations
•Test 2: reaction with silver ions Ag+
Test for the presence of chloride ion, Cl-
• Procedure:
1.
Add 1 mL of 0.5 M NaCl (or your unknown) and 1 mL of 6 M HNO3 to
a small test tube.
2.
add 2 to 3 drops of 0.1 M AgNO3 .
• Observation:
• The formation of a white, curdy precipitate
• Chemical reaction:
• Molecular reaction: NaCl (aq) + AgNO3 (aq) AgCl (s) + NaNO3 (aq)
• Complete ionic:
• Net ionic:
• In your opinion, why do we add a strong base , HNO3 in this case?
NaCl (aq) + AgNO3 (aq)
Summary of Observation
Answers to questions
Practice 1
Sodium chloride (NaCl) and lead II nitrate Pb(NO3)2:
Molecular Equation: Pb(NO3)2(aq)+2NaCl(aq)→PbCl2(s)
↓+2NaNO3(aq)
Complete Ionic Equation:
Net Ionic Equation
Practice 2
Sodium carbonate Na₂CO₃ and Iron II chloride FeCl2
Molecular Equation: FeCl2(aq) + Na2CO3(aq) → FeCO3(s) +
2NaCl(aq).
Complete Ionic Equation:
Net Ionic Equation: