A Silver/Copper Replacement Reaction

Description

Copper wire reacts with aqueous silver nitrate. The relative amounts (moles) of reactant and product are determined from the mass loss of copper wire, the starting mass of silver nitrate, and the mass of silver metal obtained.

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Copper will be changed from its elemental form, Cu, to its blue aqueous ion form, Cu²⁺(aq). At the same time, silver ions (Ag⁺(aq)) will be removed from solution and deposited on the wire in the elemental Ag metallic form.

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Handling silver nitrate solutions will lead to black stains where it is spilled. It is also poisonous. Be especially careful to avoid getting it in the eyes.

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• Wear safety goggles and lab apron; silver nitrate will stain clothes and skin. Flush with water in the event of contact.
• Wear goggles, gloves, and an apron.

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1. Obtain a 30 cm length of bare copper wire and coil it around a pencil, forming a loose coil or "spring" on one end. Stretch the coil to reach from the bottom to the top of the tube. The other end should reach to the top of your test tube and be uncoiled.
2. Make a hook on one end of the spring for weighing.
3. Weigh the coil as accurately as possible with the available balance. Place the copper wire in the test tube.
4. Weigh the vial of silver nitrate.
5. Transfer the contents (about 1.5 grams) of the silver nitrate vial to your beaker.
6. Weigh the empty vial so you can determine the mass of silver nitrate that was originally dissolved.
7. Also, weigh a piece of filter paper for use in separating the silver later.
8. Pour 20 mL of distilled water into your beaker. Use a stirring rod to stir until completely dissolved. Use caution not to poke a hole in the bottom of the beaker. To avoid stains, be sure to rinse the stirring rod with distilled water before setting it down.
9. Add the silver nitrate solution. Rinse the beaker and rod with distilled water, adding this rinse to the test tube.
10. Note any evidence for reaction in the tube.
11. Set the tube aside until the next class period.
12. The reaction can be completed during a long class period. Else, at the beginning of the next class period, shake the wire and dislodge the silver allowing it to fall to the bottom of the test tube.
13. Any silver that adheres to the wire can be rinsed back into the solution by squirting it with a stream of water from the wash bottle of distilled water. You may wish to use a beaker to wash the wire.
14. Pour off the blue solution through the filter paper into the waste beaker, being sure to keep the silver precipitate in the test tube. Rinse with distilled water and decant several times to wash the silver. Finally wash onto a filter paper. If a beaker was used to wash the wire, be sure to wash the contents of the beaker into the filter collecting silver.
15. Allow to dry overnight. An oven temperature of 75-80 °C works well.
16. Weigh the copper coil during the next class period, if necessary.
17. Cool the filter paper to room temperature.
18. Weigh the silver and filter paper.
19. Be sure you have all the data carefully recorded.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 019 A Silver/Copper Replacement Reaction

Mass of vial and silver nitrate =

Mass of empty vial =

Mass of silver nitrate =

Mass of copper coil before reaction =

Mass of copper coil after reaction =

Mass of copper reacted =

Mass of filter paper & silver =

Mass of filter paper =

Mass of silver produced in reaction =

1. Find the number of moles of silver produced.
2. Find the number of moles of copper consumed during the reaction.
3. Find the mole ratio of copper to silver in this reaction (round to the nearest whole number).
4. Write a balanced equation for the reaction using the mole ratio derived above as the coefficients.
5. During the middle ages, a group of people called alchemists searched unsuccessfully for a way to "transmute" or change one element to another, e.g. lead to gold. Was the copper "transmuted" into silver in this experiment? Explain.
6. Calculate the moles of silver nitrate in the original solution. What percentage of this was changed to silver?
7. Find the number of atoms of copper removed from the wire.
8. How would the calculated mole ratio be affected if the silver were not completely dry when weighed?
9. List any other errors that could have affected your results.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 019 A Silver/Copper Replacement Reaction

Answer these questions before watching the movie.

1. What is the color of the silver nitrate solution?
2. Predict the changes expected in the copper wire as the reaction proceeds.
3. How would you expect the solution to change as the reaction proceeds?
4. What precaution must you take in terms of handling the silver nitrate solid and solution?
5. After the silver stops forming on the wire, why is the solution less likely to cause stains on the skin and clothes?

Watch the movies and answer the following questions.

Use this sample data to calculate the answer requested below.

Mass of vial and silver nitrate = 9.05 g

Mass of empty vial = 7.89 g

Mass of silver nitrate = 1.16 g

Mass of copper coil before reaction = 1.42 g

Mass of copper coil after reaction = 1.23 g

Mass of copper reacted = 0.19 g

Mass of filter paper & silver = 1.58 g

Mass of filter paper = 0.84 g

Mass of silver produced in reaction = 0.74 g

1. Find the number of moles of silver produced.
2. Find the number of moles of copper consumed during the reaction.
3. Find the mole ratio of copper to silver in this reaction (round to the nearest whole number).
4. Write a balanced equation for the reaction using the mole ratio derived above as the coefficients.
5. During the middle ages, a group of people called alchemists searched unsuccessfully for a way to "transmute" or change one element to another, e.g. lead to gold. Was the copper "transmuted" into silver in this experiment? Explain.
6. Calculate the moles of silver nitrate in the original solution. What percentage of this was changed to silver?
7. Find the number of atoms of copper removed from the wire.
8. How would the calculated mole ratio be affected if the silver were not completely dry when weighed?
9. List any other errors that could have affected your results.

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Purpose

To determine the relative number of moles of reactant and product for a chemical reaction.

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(Per 10 students working in pairs)

• 150 cm of bare copper wire
• 5 150-mL beaker
• 5 test tube
• 5 support stand, each with a single buret clamp
• 5 funnel
• 5 pencil
• drying oven (or suitable alternate, see A51)
• 5 watch glass
• 5 vial containing 1.5 g of solid silver nitrate each
• centigram balance
• 5 wash bottles containing distilled or deionized water
• filter paper
• 5 stirring rod
• 5 50-mL graduated cylinder
• concentrated nitric acid (for silver recovery only)

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• Some brands of copper wire are lacquered and will not react adequately until the coating has been removed with steel wool. Test your wire before allowing students to begin.
• In many areas, there are sufficient chloride ions in tap water to react with the silver ion to produce a cloudy precipitate. Use distilled or deionized water.

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Teacher preparation: 30 minutes to prepare vials

Class Time: Portions of 3 class periods

• 30 minutes first period
• 15 minutes second period (wash and filter)
• 10 minutes third period (cool and weigh)

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• Handling silver nitrate solutions will lead to black stains where it is spilled. It is also poisonous. Be especially careful to avoid getting it in the eyes.
• Concentrated nitric acid used in the recovery process is corrosive.

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• Wear safety goggles and lab apron; silver nitrate will stain clothes and skin. Flush with water in the event of contact.
• Wear goggles, gloves, and an apron.

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• The copper solution may be disposed of at the sink in most communities. Except for the silver metal, other materials may be disposed of with routine trash.
• Waste silver is acutely hazardous. Do not pour any silver compounds into the sink.
• Silver formed during the experiment should be recycled for qualitative use as silver nitrate by using the following procedure:
  1. Soak the silver with a small amount of excess silver nitrate solution for 24 hours to react small particles of copper that may have broken off. (Otherwise the solution will have a blue tinge)
  2. Filter and wash.
  3. Add excess concentrated nitric acid under a hood and boil gently until dissolved.
  4. Continue boiling until nearly dry. Decant and redissolve the precipitate with distilled water.
  5. Filter and boil to near dryness again. Collect crystals by filtration.
  6. Redissolve and filter one more time. This solution is acceptable for any qualitative use of silver nitrate solution.

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Set Questions:

1. What is the color of the silver nitrate solution?
2. Predict the changes expected in the copper wire as the reaction proceeds.
3. How would you expect the solution to change as the reaction proceeds?
4. What precaution must you take in terms of handling the silver nitrate solid and solution?
5. After the silver stops forming on the wire, why is the solution less likely to cause stains on the skin and clothes?

Answers to Set Questions:

1. Colorless.
2. The copper wire should show evidence of "turning to" or producing silver.
3. The solution should contain copper ions as the reaction proceeds, which means it will turn blue.
4. Silver nitrate will stain skin and clothes if it contacts them.
5. Once the wire stops reacting, nearly all of the silver has been chemically converted from aqueous silver ion to silver metal. Silver metal does not react with skin.

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Presentation Question:

• What would happen if an equal length of very fine copper wire were used in this experiment?
  • A fine copper wire might not provide enough copper metal to react with all of the silver. In this event, all of the wire in the solution would dissolve, and some silver ions would remain dissolved in the solution.

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Mass of vial and silver nitrate = 9.05 g

Mass of empty vial = 7.89 g

Mass of silver nitrate = 1.16 g

Mass of copper coil before reaction = 1.42 g

Mass of copper coil after reaction = 1.23 g

Mass of copper reacted = 0.19 g

Mass of filter paper & silver = 1.58 g

Mass of filter paper = 0.84 g

Mass of silver produced in reaction = 0.74 g

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Closure Questions:

1. Find the number of moles of silver produced.
2. Find the number of moles of copper consumed during the reaction.
3. Find the mole ratio of copper to silver in this reaction (round to the nearest whole number).
4. Write a balanced equation for the reaction using the mole ratio derived above as the coefficients.
5. During the middle ages, a group of people called alchemists searched unsuccessfully for a way to "transmute" or change one element to another, e.g. lead to gold. Was the copper "transmuted" into silver in this experiment? Explain.
6. Calculate the moles of silver nitrate in the original solution. What percentage of this was changed to silver?
7. Find the number of atoms of copper removed from the wire.
8. How would the calculated mole ratio be affected if the silver were not completely dry when weighed?
9. List any other errors that could have affected your results.

Answers to Closure Questions:

1. 0.74 g Ag⁺ x (1 mol Ag/ 107.9 g Ag) = 0.0069 mol Ag
2. 0.19 g Cu x (1 mol Cu/ 63.5 g Cu) = 0.0030 mol Cu
3. 0.0069 mol Ag/0.0030 mol Cu = 2.3 Ag/1.0 Cu ≅ 2 Ag/1 Cu
4. 2 AgNO₃ + Cu --> 2 Ag + Cu(NO₃)₂
5. No. Copper changed from an atomic, metallic, unreacted state to an aqueous ion form. The silver came from the Ag⁺ in the silver nitrate solution.
6. 1.16 g AgNO₃ x 1 mol/169.9 g AgNO₃=

   0.00682 mol AgNO3 (0.0069 mol Ag/0.00683 mol AgNO₃) x 100= 101%

7. 0.0030 mol Cu x 6.02 x 10²³ atoms/1 mol Cu = 1.8 x 10²¹ atoms.
8. It would be too high; the mass of the water would be thought to be silver.
9. Improper weighing; loss of silver in filtration; dissolved Cu(NO₃)₂ remaining in the filter paper; copper reacting with something other than silver.

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• replacement reaction
• redox
• balanced equation
• mole relationship
• mole

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