Exp' 35 Qual 1' Na , K , NH4 , Ag , Cu2 , Bi3 p' 393

1
Exp. 35 Qual 1. Na, K, NH4, Ag, Cu2, Bi3
p. 393

• To observe and utilize the chemical and physical
  properties of Na, K, NH4, Ag, Cu2, and Bi3
  to separate and identify the presence of one or
  more of these cations in an aqueous solution.

2
Exp. 35 Introduction

• In identifying a particular cation in a mixture
  of
• cations, they must first be separated into
• groups having similar chemical properties
• each group is then further divided until each
• ion is isolated.
• The cation then will respond to a reagent to
• produce a characteristic color or precipitate.

3
Exp. 35 Introduction

• Keep in mind the following
• Most Na, K, and NH4 salts are soluble.
• The chloride salt of Ag is insoluble.
• The sulfide salts of Cu2 and Bi3 are also
  insoluble.
• Na is a universal impurity so is identified
  after all other interfering ions have been
  removed.
• pH control is very important in the separation of
  Bi3 and Cu2 from the Qual II cations.

4
Exp. 35 Introduction

• Sodium Ion
• Na produces a characteristic fluffy yellow
• flame.
• Potassium Ion
• K produces a lavender color when viewed
• through a cobalt blue glass (which absorbs
• the yellow caused by the Na).

5
Exp. 35 Introduction

• Ammonium Ion
• When OH- is added to a solution containing
• NH4, the equilibrium shifts left, and, upon
  heating,
• ammonia gas is released and detected with litmus
• paper (or by its odor).
• ?
• ?
• NH3(g) H2O(l) ? NH4(aq) OH-(aq)
• 
  ?OH-(aq)

6
Exp. 35 Introduction

• Silver Ion
• When a moderate amount of HCl is added to a
• solution containing Ag, AgCl precipitates.
• AgCl dissolves in ammonia to form Ag(NH3)2
• complex which is unstable in an acidic solution.
  
• Adding H3O causes the equilibrium to shift to
• the left and AgCl reforms as a white ppt.

7
Exp. 35 Introduction

• Copper Ion
• The addition of NH3 to a solution containing Bi3
  
• and Cu2 cations precipitates white bismuth
• hydroxide and complexes Cu2 as a deep blue
• Cu(NH3)42 complex.
• A confirmatory test for Cu2 is the addition of
• potassium hexacyanoferrate(II), K4Fe(CN)6,
  which
• produces a red-brown ppt of Cu2Fe(CN)6.

8
Exp. 35 Introduction

• Bismuth Ion
• The solid, white Bi(OH)3 is dissolved and
• confirmed with the addition of fresh sodium
• stannite, Na2Sn(OH)4, in a basic solution.
• The Bi3 ion is reduced to black bismuth
• metal.

9
Exp. 35 Procedural Notes

• Part A.1. Be careful, you will be using
  Ca(OH)2, a corrosive chemical.
• Part C.1. Not a continuation of A or B. Do not
  heat the solution to dryness.
• Part D.1. Add 4-5 drops of 6M HCl.
• Part D.2. My unknown did not dissolve you may
  need to use additional NH3.
• Part E. Omit
• No Questions