MHS Chemistry
Extraction of Silver from an Alloy

The purpose of this lab is for you to extract silver from a sample of sterling silver and determine the mass percent of silver in the alloy.  Follow all lab safety precautions!


Before Starting
1. Find the formula for nitric acid: _____________________
2. Find the formula for sulfuric acid: _____________________
3. Find the formula for hydrochloric acid: _____________________
4. Define decant: __________________________________________

Procedure - First Lab Day

  1. Obtain a piece of silver-copper alloy (sterling silver) about one inch long, and mass it to the nearest 0.001 gram.  Record the mass.
  2. Prepare a hot water bath by half-filling a 400 mL beaker with water.  Heat the water to boiling.
  3. Place the alloy in an evaporating dish and add about 5 mL of 8 M nitric acid.  Place the evaporating dish on top of th beaker, and boil the water gently.  Allow the acid solution to evaporate over the hot water bath.
  4. The metal should dissolve before the acid completely evaporates.  If it does not dissolve completely, add a little more nitric acid.  Continue heating until the solution in the dish has completely evaporated.
  5. Add about 3 mL of dilute sulfuric acid.  Tilt the dish to make sure the acid comes in contact with all the residue in the dish.  Again evaporate completely.
  6. Remove the dish from the water bath and let cool.  When cool, go to the hood and add about 8 mL of ammonium hydroxide, then stir.  The solid in the dish should completely dissolve forming a deep blue solution.
  7. Transfer the contents of the dish to a 250 mL beaker.  Obtain about 125 mL of distilled water and rinse the contents of the dish into the beaker adding all of the distilled water to the beaker.
  8. Add dilute sulfuric acid to the beaker slowly and with constant stirring until the solution tests acid with litmus paper.  Blue litmus paper changes to red in acid.
  9. Now slowly add an additional 25 mL of dilute sulfuric acid to the beaker while stirring constantly.  If any precipitate exists, heat and stir the contents of the beaker until dissolved but do not boil it.
  10. Allow the solution to cool. Obtain about 30 cm of stripped copper wire and coil it into a several large loops. Leave some of the wire to act as a handle sticking out of the solution.
  11. Place the copper coil in the acid solution and hook the handle over the rim.  Submerge as much of the copper as possible in the solution.
  12. Let this stand a few minutes and observe the results.  Agitate the coil to remove the attached silver, and observe that new silver crystals begin to form immediately.
  13. Cover the bottle and mark it with your names.  Store the bottle until the next lab period to allow complete deposition of the silver.
Procedure - Second Lab Day
  1. To determine if all of the silver has been deposited, test the solution in the bottle for the presence of silver ions.  To do this, transfer a few drops of the solution to a small test tube and add one or two drops of hydrochloric acid.  If a white precipitate or cloudiness appears, there are still silver ions present in solution.  Go back to Day 1/Step 12.
  2. When the separation of silver is complete, shake off any crystals of silver that might remain on the wire and return the wire to your teacher.
  3. Let the silver settle and decant as much of the solution as possible into a clean beaker.  Be careful not to lose any of the silver crystals.  Add about 5 mL of distilled water to the remaining solid and mix thoroughly with a stirring rod.  Decant the water into the beaker.  If no silver has been poured out by accident, pour the water into the waste container provided.
  4. Wash the silver with 5 to 10 mL of distilled water several times.  Pour the washings into a small beaker and test for copper by adding a few drops of concentrated ammonium hydroxide.  If the solution turns blue, wash it again.  Discard the washings as instructed.  Repeat the washing until a copper test made on the wash water is negative (think: what is a negative test?).
  5. Clean an evaporating dish and make sure it is dry by heating it with a Bunsen burner.  Cool the dish and mass it to the nearest 0.001 gram.  Record the mass.
  6. Transfer the silver to the evaporating dish and heat until the silver is completely dry.  An oven ir preferable, to avoid splattering. Allow to cool before weighing.  Dry to a constant mass.
  7. Calculate the mass of silver in the alloy.
  8. Calculate the mass percent of silver in the alloy.
What to Pass In

[Extraction of Silver score sheet][MHS Chem page]