white powder analysis

Topics: Solubility, Precipitation, Sodium chloride Pages: 3 (602 words) Published: October 9, 2014

Lab Write Up
Pre-Lab Questions:
1. What precipitation reaction could be used to separate and remove silver ions from a mixture containing iron (III) and zinc ions? A precipitation reaction that could be used is hydrochloric acid Ag+(aq) + HCl(aq) AgCl(s) +H+(aq) – white. 2. What precipitation reaction could be used to separate and remove iron (III) ions from the remaining mixture containing iron (III) and zinc ions? Fe3+(aq) + 3NaOH(aq)  Fe(OH)3(s) + 3Na+(aq)

3. How can the presence of silver ions be positively identified? AgCl(s) +2NH3(aq)  Ag(NH3)2+(aq) + Cl-(aq)
4. How can the presence of iron (III) ions be positively identified? Fe(OH)3(s) + 3HCl(aq) + SCN- (aq)  FeSCN2+ (aq) + 3Cl- (aq) + 3H2O(l) 5. How can the presence of zinc ions be positively identified? Zn(OH)4 2-(aq) + 4HCl(aq)  Zn2+(aq) + 4H2O(l) + 4Cl-(aq)

Post-Lab Questions:
1. What cation(s) are present in the unknown sample? How do you know? The cation(s) present in the unknown sample are silver and iron. I know this because the precipitates and the colors of the elements precipitates matched therefore making the unknowns identifiable. 2. Write a net ionic equation for each of the following steps in the qualitative analysis scheme. a) Separation of silver ions, Ag+

Ag + (aq) + HCl(aq) AgCl(s) + H+(aq)
Ag +(aq) + H+(aq) + Cl-(aq) AgCl(s) + H+(aq)
Ag+(aq) + Cl-(aq)  Ag+Cl-(s)
b) Confirmation of silver ions, Ag+
AgCl(s) + 2NH3(aq)  Ag(NH3)2+(aq) + Cl-(aq)
Ag+Cl-(s) + 2N(aq) + H3+(aq)  Ag+(aq) + (NH3)2+(aq) + Cl-(aq) c) Separation of iron (III) ions, Fe3+
Fe3+ (aq) + 3NaOH (aq) Fe(OH)3 (s) + 3Na+ (aq)
Fe3+ (aq) + 3Na+(aq) + 3H2O(aq)  Fe(OH)3(s) + 3Na+(aq)
Fe3+ (aq) + 3H2O(aq)  Fe(OH)3(s)
d) Confirmation of iron (III) ions, Fe3+ Fe(OH)3(s) + 3HCl(aq) + SCN-(aq) FeSCN2+(aq) + 3Cl-(aq) +3H20(l) Fe(OH)3(s) + 3H+(aq) + 3Cl-(aq) + S2-(aq)+C(aq)+N2+(aq) +3Cl-(aq) +3H20(l) Fe(OH)3(s) + 3H+(aq) ) + S2-(aq)+C(aq)+N2+(aq)...
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