Question: You have been given four unknown solutions, each containing one salt. These salts may cont — Qualitative Analysis Chemistry Question

Students should include:
- Using provided solutions to qualitatively test unknowns for chemical change.
- Use of spot plates
- Testing with pH strips (ok if they didn’t put it in procedure but did it in trials)
- Use process of elimination for determining anions and cations.
- Record observations on table?
- Have examiner’s intial. (1 pt separate)

Students should include:
- A data table
- Record observations for bubbling, precipitation, smell
- Recording pH may be useful
- Maybe include statements of justification
-1 in tables if you do not mention concentrations: i.e different NaOH concentrations

Sample observations expected:
Unknown Solution 1 (0.1 M MgCl₂): pH 6-7; ppt with 0.01 M AgNO₃; No Reaction with 1.0 M HCl; ppt with 0.1 M NaOH; ppt with 1.0 M NaOH; ppt with 0.1 M Na₃PO₄.
Unknown Solution 2 (0.1 M Ca(OAc)₂): pH 6; No Reaction/faint ppt with 0.01 M AgNO₃; No Reaction/Faint smell of vinegar with 1.0 M HCl; no ppt/very little with 0.1 M NaOH; ppt with 1.0 M NaOH; ppt with 0.1 M Na₃PO₄.
Unknown Solution 3 (Sat. NH₄NO₃): pH 4-5; No Reaction with 0.01 M AgNO₃; No Reaction with 1.0 M HCl; No Reaction/faint NH₃ smell with 0.1 M NaOH; Smell of ammonia/bubbles with 1.0 M NaOH; No Reaction with 0.1 M Na₃PO₄.
Unknown Solution 4 (0.5 M Na₂CO₃): pH 11; ppt with 0.01 M AgNO₃; bubbles with 1.0 M HCl; No Reaction with 0.1 M NaOH; No Reaction with 1.0 M NaOH; No Reaction with 0.1 M Na₃PO₄.

Unknown 1 Contains: MgCl₂. Justification: 0.01 M AgNO₃ – big precipitate - could be Cl^-, CO₃ 2-. 1.0 M HCl – NR – rules out CO₃ 2-. 0.1 M Na₃PO₄ – big precipitate – Could be Mg²⁺, Ca²⁺. 1.0 M NaOH – big precipitate – Could be Mg²⁺, Ca²⁺. 0.1M NaOH - precipitates Mg²⁺ but not the 0.1M Ca²⁺ (Introductory Solubility Rules indicate Ca(OH)₂ is soluble, however the solubility is low) pH 6-7; vague, but fits literature range. Would think MgCl₂ would be lower pH than Ca(OAc)₂ but they were very similar. Possible ion combinations: Mg²⁺ Ca²⁺ NH⁴⁺ Na⁺ Cl^- OAc^- NO₃ - CO^32-
Unknown 2 Contains: Ca(OAc)₂. Justification: 0.01 M AgNO₃ – no or very small amount of ppt; this is important for I.D. between nitrate and acetate. While acetates as a “general rule” are considered soluble, silver acetate has a Ksp of 2*10-3. 1.0 M HCl –No Reaction – rules out CO₃ 2- smell indicates acetate. 1.0 M NaOH – precipitate– Could be Mg²⁺, Ca²⁺ 0.1 M NaOH – no or faint precipitate–Ca²⁺ 0.1 M Na₃PO₄ – precipitate – Could be Mg²⁺, Ca²⁺ pH 6;pKa of H₂O for Mg²⁺ is about 12 and for Ca²⁺ is about 11. Probably not different enough to tell the difference with pH paper. Other reaction data should be able to determine ion presence. Possible ion combinations: Mg²⁺ Ca²⁺ NH⁴⁺ Na⁺ Cl^- OAc^- NO₃ - CO^32-
Unknown 3 Contains: NH₄NO₃. Justification: 0.01 M AgNO₃ – No Reaction – rules out Cl^-, CO₃ 2. 1.0 M HCl – No Reaction – rules out CO₃ 2- 1.0 M NaOH – no clear bubbling, but visual evidence suggesting a reaction. Smell of ammonia. Suggests NH⁴⁺. No ppt rules out Mg²⁺, Ca²⁺ 0.1 M NaOH – N.R. visible maybe faint NH₃ smell 0.1 M Na₃PO₄ – ppt – rules out Mg²⁺, Ca²⁺ pH 4 – indicates an acidic cation. Possible ion combinations: Mg²⁺ Ca²⁺ NH⁴⁺ Na⁺ Cl^- OAc^- NO₃ - CO^32-
Unknown 4 Contains: Na₂CO₃. Justification: 0.01 M AgNO₃ – precipitate - Cl^-, CO₃ 2. 1.0 M HCl – bubbles indicates CO₃ 2. 1.0 M NaOH – No Reaction 0.1 M NaOH - No Reaction 0.1 M Na₃PO₄ – No Reaction pH 11 – indicates a basic anion. Possible ion combinations: Mg²⁺ Ca²⁺ NH⁴⁺ Na⁺ Cl^- OAc^- NO^3- CO^32-