Silver Alloy lab. Warm-up Mg + O 2 MgO What is the % composition of Mg in MgO? If I start with a 5.0g sample of Mg, what mass of MgO should I get (assuming.

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Silver Alloy lab

Warm-up Mg + O 2 MgO What is the % composition of Mg in MgO? If I start with a 5.0g sample of Mg, what mass of MgO should I get (assuming the Mg burns completely in excess O 2 )? 24/40 = 60% 5/60% = 8.3g

Purpose To determine the % by mass of Ag in sterling silver To determine the % by mass of Ag in sterling silver Also… To practice quantitative Chemistry separation methods Also… To practice quantitative Chemistry separation methods Quantitative lab methodto determine amounts present Quantitative lab methodto determine amounts present Qualitative lab methodto determine presence or absence Qualitative lab methodto determine presence or absence

The chemistry involved Must oxidize (ionize by removing electrons) the Ag and other metal(s) into ions so they will dissolve in water. Must oxidize (ionize by removing electrons) the Ag and other metal(s) into ions so they will dissolve in water. Normally acids are used to oxidize metals Normally acids are used to oxidize metals Normally acids are used to oxidize metals Normally acids are used to oxidize metals H + is only a fair oxidizing agent H + is only a fair oxidizing agent NO 3 - in acid solution is stronger NO 3 - in acid solution is stronger HNO 3 used to oxidize the alloy, get metal ions into solution. HNO 3 used to oxidize the alloy, get metal ions into solution.

To separate Ag + Ag will be dissolved (turned into Ag + ) from sterling silver using nitric acid. Ag will be dissolved (turned into Ag + ) from sterling silver using nitric acid. Since AgCl is insoluble, add Cl - to the solution and Ag + precipitates out as AgCl Since AgCl is insoluble, add Cl - to the solution and Ag + precipitates out as AgCl Most metal chlorides are soluble (except those of Ag, Hg, Pb), so ALL other metal ions stay in solution Most metal chlorides are soluble (except those of Ag, Hg, Pb), so ALL other metal ions stay in solution Note: Could also use I - or Br - Note: Could also use I - or Br -

Overall 1. Clean and set up the lab equipment 2. Weigh your alloy sample 3. Dissolve the alloy in acid Metals + HNO 3 Metal(NO 3 ) (aq) + H 2 O + NO (g) 4. Precipitate the Silver Metal(NO 3 ) (aq) + NaCl (aq) NaNO 3(aq) + Metal(Cl) Since silver chloride is insoluble, it will crystallize out (overnight) But, copper chloride will remain aqueous 5. Filter out the AgCl made 6. Dry and weigh the AgCl 7. Calculate the mass of Ag (in AgCl) and then determine the % Ag in your original sample Were actually doing #1-4 tomorrow

Add to your procedure: 8. Calculate the percentage error of your result… Sterling silver is 92.5% silver

Mass of sterling sampleg Mass of NaCl neededg Mass of labeled filter + dishg Mass of filter + dish + AgClg Mass of AgClg Mass of Ag in AgClg % Ag in Sterling% % Error% Data Table You must show your work for all calculations in an analysis section

Write-up Purpose Question Purpose Question Data Collection and Analysis: Data Collection and Analysis: Data Table (include qualitative observations) Data Table (include qualitative observations) Calculations Calculations Conclusion and Evaluation: Conclusion and Evaluation: Conclusion Conclusion Sources of Error with HOW each would affect the data Sources of Error with HOW each would affect the data Improvements Improvements

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