Cathy Notes

Topics: Silver, Solubility, Silver nitrate Pages: 6 (1473 words) Published: September 20, 2012
Sample Analysis. Precipitates and Complexes of Silver Ion

Data for Determining Formulas

Solutions containing NH3, CO32–, Cl–, I–, PO43–, and S2O32– ions were added to equal proportions of a silver nitrate solution, which contained the complex ion Ag(H2O)2+. All of the added solutions were also clear and colorless. |AgNO3 (aq) by itself |Colorless solution | |AgNO3 (aq) with NH3 (aq) |Colorless solution | |AgNO3 (aq) with Na2CO3 (aq) |Pale yellow precipitate | |AgNO3 (aq) with NaCl (aq) |White precipitate | |AgNO3 (aq) with NaI (aq) |Yellow precipitate | |AgNO3 (aq) with Na3PO4 (aq) |Yellow precipitate | |AgNO3 (aq) with Na2S2O3 (aq) |Colorless solution |

Formulas of Silver Complexes and Precipitates

Ag+ ions formed precipitates with CO32–, Cl–, I–, and PO43– ions. Solids are electrically neutral; the charges of all their ions add up to zero. Therefore, the formulas of these precipitates are: Ag2CO3, AgCl, AgI, and Ag3PO4. It is not obvious from these observations that Ag+ ions formed soluble complex ions with NH3 and S2O32– ions. However, data on the next page shows that solutions containing NH3 and S2O32– ions were able to convert the pale yellow precipitate Ag2CO3 into colorless solutions. Thus, complex ions more stable than Ag2CO3 must have formed. Ag+ has a coordination number of 2, so it binds to two ligands when it forms complex ions. The formulas of the complex ions formed with NH3 and S2O32– are therefore: Ag(NH3)2+ and Ag(S2O3)23–. The product-favored reactions that occurred when NH3 (aq) and Na2S2O3 (aq) solutions were added to Ag2CO3 (s) were: Ag2CO3 (s) + 2 NH3 (aq) (( 2 Ag(NH3)2+ (aq) + CO32– (aq) Ag2CO3 (s) + 2 S2O32– (aq) (( 2 Ag(S2O3)23– (aq) + CO32– (aq) |Ag(H2O)2+ (aq) |Colorless solution | |Ag(NH3)2+ (aq) |Colorless solution | |Ag2CO3 (s) |Pale yellow precipitate | |AgCl (s) |White precipitate | |AgI (s) |Yellow precipitate | |Ag3PO4 (s) |Yellow precipitate | |Ag(S2O3)23– (aq) |Colorless solution |

Data for Determining Relative Stabilities
In order to rank the observed precipitates and complex ions in order of stability, solutions containing NH3, CO32–, Cl–, I–, PO43–, and S2O32– ions were again added to equal proportions of a silver nitrate solution. Then a third portion of a second solution, also containing NH3, CO32–, Cl–, I–, PO43–, or S2O32– ions was added.

|Added 2nd |NH3 |CO32– |Cl– |I– |PO43– |S2O32– | |Added 1st | | | | | | | |NH3 |X |No change |Change to white...
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