In the reaction between lead nitrate and potassium iodide which other substance can be used instead of lead nitrate to obtain the same result?
Answers
Explanation:
Double Replacement Reactions
Introduction
Combine potassium iodide and lead(II) nitrate to introduce students to the topic of double replacement reactions!
Concepts
• Solubility • Precipitation • Double replacement reactions
Background
Potassium iodide and lead(II) nitrate are combined and undergo a double replacement reaction. Potassium iodide reacts with
lead(II) nitrate and produces lead(II) iodide and potassium nitrate. Potassium nitrate is water soluble. However, lead(II) iodide is
only partially soluble in water. Most of the lead(II) iodide precipitates out of the solution as a yellow solid (Equation 1).
2KI(s) + Pb(NO3)
2(s) → 2KNO3(aq) + PbI2(s) Equation 1
The potassium iodide and lead(II) nitrate are added to opposite sides of a Petri dish that contains water. Both ionic compounds
will separate into their individual ions. Once the ions are separated, they are hydrated by the water in the Petri dish, which
allows them to be carried in solution. The lead ions and iodide ions will eventually meet to form a yellow precipitate. They do
not meet exactly in the middle of the Petri dish. The reaction takes place closer to the side of the dish where lead was initially
added. The iodide ions are able to migrate further faster due to their smaller atomic mass. The lead ions are heavier and larger
so they take longer to separate, hydrate and migrate through the solution.
Materials
Lead(II) nitrate, Pb(NO3)
2, 1 g Overhead projector
Potassium iodide, KI, 2 g Petri dish
Water, distilled or deionized Ring, support
Beaker, 250-mL, 2 Scoop, metal, 2
Filter paper Support stand
Funnel
Safety Precautions
Lead nitrate is moderately toxic by inhalation and ingestion, a strong oxidant and a dangerous fire risk when in contact with organic mate-
rial. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water
before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, han-
dling and disposal information.
Procedure
1. Fill a Petri dish approximately half full with distilled or deionized water.
2. Using a clean metal scoop, obtain approximately one gram of potassium iodide and set it aside next to the Petri dish.
3. Using a second clean metal scoop, obtain approximately one gram of lead(II) nitrate. Note: The exact amount is not crucial
as long as the amounts of potassium iodide and lead(II) nitrate are roughly equal.
4. Add the entire contents of both scoops to opposite sides of the Petri dish.
5. Allow the reaction to take place until a yellow precipitate is formed.
6. After observations have been made, stir the solution until it exhibits a uniform yellow color.Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review
all federal, state and local regulations that may apply, before proceeding.
Disposal Preparation Procedure
1. Set up a support stand with a ring support clamp, funnel, filter paper and a 250-mL beaker to collect the waste.
2. Pour the resulting solution from the Petri dish into a 250-mL beaker.
3. Add another scoop full of potassium iodide to react with any lead ions that may still be in solution. Stir.
4. Carefully pour the solution through the filter. Note: If done properly, the yellow precipitate will all be trapped by the filter
paper, and the filtrate in the beaker will be clear.
5. Use a wash bottle containing distilled water to rinse the beaker and Petri dish over the filter to clean out any excess lead
iodide.
6. Test the filtrate by stirring in additional potassium iodide. If the solution remains clear, it is potassium nitrate and may be
disposed of according to Flinn Suggested Disposal Method #26b. If it turns yellow, there are still unreacted lead ions in the
system, so repeat steps 2–6.
7. The precipitate (lead iodide) must be disposed of by a licensed hazardous waste disposal company according to Flinn
Suggested Disposal Method #27f.
Tips
• A Beral-type pipet may be used as a substitute for a metal scoop. Using scissors, remove half the bulb and use the remain-
ing portion of the bulb as a scoop.
• The following ionic compounds may be substituted for potassium iodide and lead(II) nitrate to avoid producing a pre-
cipitate containing lead. Silver nitrate, AgNO3, and sodium bromide, NaBr, or calcium nitrate, Ca(NO3)
2, and sodium
sulfate, Na2SO4.