Name Date Laboratory Instructor Desk Unknown no #07 REPORT SHEET Abbreviated Qualitative Analysis Scheme EXPERIMENT 32 PART I: GROUP 1 CATIONS Record the reagent used in each step, your observations, and the equations for each precipitation reaction. Procedure Reagent Observations Equations Mark (+) if observed in unknown G1-1 KSCN yellow + G1-2 NH
dark grey + G1-3 HNO
Clear Cations in group 1 unknown
Name Date Laboratory Instructor Desk Unknown no #07 REPORT SHEET Abbreviated Qualitative Analysis Scheme EXPERIMENT 32 PART I: GROUP 1 CATIONS Record the reagent used in each step, your observations, and the equations for each precipitation reaction. Procedure Reagent Observations Equations Mark (+) if observed in unknown G1-1 KSCN yellow + G1-2 NH
dark grey + G1-3 HNO
Clear Cations in group 1 unknown
The Correct Answer and Explanation is:
REPORT SHEET: Abbreviated Qualitative Analysis Scheme
EXPERIMENT 32 – PART I: GROUP 1 CATIONS
Unknown No. 07
| Procedure | Reagent | Observations | Equations | Observed in Unknown |
|---|---|---|---|---|
| G1-1 | KSCN | Yellow precipitate forms | Fe³⁺ + SCN⁻ → [Fe(SCN)]²⁺ (blood red or yellow complex) | ✔️ |
| G1-2 | NH₄OH | Dark grey precipitate | Ag⁺ + NH₃ + H₂O → [Ag(NH₃)₂]⁺ (soluble), then → Ag ↓ | ✔️ |
| G1-3 | HNO₃ | Clear solution | PbCl₂ dissolves in hot water, no precipitate seen | ✔️ |
Cations in Group 1 Unknown:
Fe³⁺, Ag⁺, Pb²⁺
Explanation
In qualitative inorganic analysis, Group 1 cations typically include Ag⁺ (silver), Pb²⁺ (lead), and Hg₂²⁺ (mercury(I)), but in some schemes, Fe³⁺ (iron(III)) may also be tested early due to distinctive reactions. The goal is to identify which of these cations are present in an unknown sample (#07), based on their reactions with specific reagents.
- G1-1 (KSCN Test):
When potassium thiocyanate (KSCN) is added, the formation of a yellow to blood-red complex indicates the presence of Fe³⁺. The thiocyanate ion reacts with ferric ion to form the [Fe(SCN)]²⁺ complex. The appearance of a yellow precipitate confirms Fe³⁺ in the unknown. - G1-2 (Ammonia Test):
Ammonium hydroxide (NH₄OH) reacts with Ag⁺ ions to form initially a brown precipitate of Ag₂O or AgOH, which may turn dark grey due to the reduction of silver ions to metallic silver. The dark grey precipitate confirms the presence of Ag⁺. - G1-3 (Nitric Acid Test):
When nitric acid (HNO₃) is added, it dissolves any basic precipitates like AgOH or Pb(OH)₂. If the solution becomes clear, this suggests dissolution of a lead or silver compound. Since the precipitate dissolves, Pb²⁺ is likely present as PbCl₂, which is soluble in hot water and does not precipitate in acidic conditions.
Based on the observations at each step, Fe³⁺, Ag⁺, and Pb²⁺ are all indicated in the unknown. This experiment demonstrates how systematic qualitative analysis allows the identification of multiple ions based on selective precipitation and color changes.
