F.6/7 Chemistry Practical: Establishing an Equation for a Reaction

Objective: To establish an ionic equation for the reaction between copper and silver ion

Group size: Two-students

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Theory:Give principle/reason to explain how is an ionic equation for the reaction between copper and silver ion is established in this experiment. The following questions should be useful to you.

  1. If copper wire is added to a solution of silver nitrate solution, what chemical change(s) will be observed? Write word equation(s) for the chemical change(s).
  2. Explain the chemical change(s) you give in (1).
  3. Suppose that you do not know the stoichiometric coefficients for the equation(s) you give in (1), it is the objective of this practical to estimate them. Outline the method of this practical (We assume that the charge of silver ion is one while the charge of copper(II) ion is an unknown.)

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Chemicals: 150 cm3 silver nitrate solution (3 litres), copper wire of about 10 cm long

Additional Apparatus:Balance, readable 0.001 g; oven or heat lamp to dry silver crystals andoven.

Safety Precaution:

Silver nitrate is harmful. If solution of silver nitrate is spurted onto your skin, black spot will be produced within one day and the spot will last for several days.

Procedure

Record your results immediately after you get the readings.Wear goggle in the course of the practical Distilled water may be replaced by de-ionized water.

  1. Cut a piece of copper wire of about 30 cm long. Place the wire under bench hydrochloric acid for about 10 minutes.
  2. Dry the wire by placing it in oven or placing it on a white tile under a 60 W lamp.
  3. Wrap the wire around a boiling tube to form a coil but leave about 8 cm straight for a handle.
  4. Weigh the copper coil to the nearest 0.001 g.
  5. Weigh a clean dry 250 cm3 beaker to the nearest 0.001 g. Fill the beaker half full of 0.10 M silver nitrate solution.
  6. Bend the handle of the weighed copper wire such that it can be hung over the edge of the beaker with the coil immersed in the silver nitrate solution. Cover the beaker with awatch-glass.
  7. In the next laboratory period, take out the beaker carefully and observe what has happened.
  8. Shake the crystals off the coil and lift the coil. Use a wash-bottle to rinse any crystals into the beaker.
  9. Allow the coil to dry and reweigh the coil.
  10. Let the crystals settle in the beaker. Carefully decant the solution. Add about 5 cm3 of 0.10 M silver nitrate solution to the crystals. Stir the mixture, allow solid to settle, and decant again with care.
  11. Wash the residue with about 10 cm3 of distilled water and decant carefully. Wash and decant two more times.
  12. Place the beaker and its contents in a drying oven to dry the silver residue. Weigh the silver residue.

Data and results

Observation for the reaction:

Initial mass of copper wire=

Final mass of copper wire=

Mass of copper reacted=

Mass of beaker=

Mass of beaker + silver crystals=

Mass of silver crystals=

Calculation: Calculate number of moles of copper and that of silver reacted in this experiment and hence the mole ratio of copper and silver ion.

Discussion(deduction from the results)

  1. Based on your results write an equation for the reaction.Calculate percentage error for your stoichiometric coefficients.
  2. Discuss your results (e.g. are the results reliable?) Can this experimental method applied to other reactions such as the reaction between magnesium and iron sulphate? Explain.
  3. In step 6, the beaker is covered with watch glass. Give reason for doing this step.
  4. In step 10, a further 5 cm3 of silver nitrate solution is added. Explain.
  5. What error will be resulted if tap water is used instead of distilled water in step 8 and 11? (Note that your final answer for this question is positive error or negative error. Show how do you get your answer.)

The Report: Hand in your report to Mr. Lam (The Preparation Room) before 4:30 p.m.

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Mole_03/Mole ratio for silver ion and copper /p.