MHS Chemistry
Continuous Variation (Pb & I)

Data 1 - Pre-Lab
Each student must complete this section before working with any chemicals in this lab.
 
my partner is: _________________________
moles of potassium iodide required: _________________________
moles of lead nitrate required: _________________________
formula weight of potassium iodide: _________________________
concentration of lead nitrate: _________________________
Mr. Zahm's check-off: _________________________

Calculate the mass of potassium iodide you will be using.  Show your calculations, remember to use the factor/label method, and don't round anything off until the final result.
 
 
 
 

Calculate the volume in Liters of lead nitrate solution you will need.
 
 
 
 

Convert the volume of lead nitrate to milliliters.
 
 
 
 

Procedure

  1. Dissolve your potassium iodide in about 50 mL of distilled water in a 250 mL beaker.
  2. Dispense the calculated volume of lead nitrate solution into a 150 mL beaker.  Record the initial and final volumes from the buret exactly as you read them.
  3. Combine the two solutions in the larger beaker.  Swirl and stir gently.
  4. Collect the solid precipitate by filtration.  Dry the filtered precipitate by heating gently as demonstrated.
  5. When the residue (the dried filtrate) is dry, record the mass of the residue and filter paper together.
  6. Discard the filtrate (solution that passes through the filter paper) in the metal waste bucket.
Data 2
mass of weighing dish _________________________ _g_
actual mass of weighing dish + potassium iodide _________________________ ___
initial volume buret _________________________ ___
final volume of buret _________________________ ___
mass of filter paper _________________________ ___
mass of filter paper + precipitate _________________________ ___

 
 
Results 2
mass of potassium iodide actually used _________________________ _g_
volume of lead nitrate actually used _________________________ ___
mass of precipitate _________________________ ___
color of precipitate _________________________ ___

Analysis - Class Data
 
Group moles potassium iodide moles lead nitrate mass of precipitate (g)
____________________ ____________________ ____________________ ____________________
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____________________ ____________________ ____________________ ____________________
____________________ ____________________ ____________________ ____________________
____________________ ____________________ ____________________ ____________________
____________________ ____________________ ____________________ ____________________
____________________ ____________________ ____________________ ____________________
____________________ ____________________ ____________________ ____________________

  1. Make a graph of the class results, with mass of precipitate vs. moles of potassium iodide (Before you begin, which one is the x-axis?  What are your scales?).

  2. Add another x-axis above the graph, with moles of lead nitrate added.

  3. Draw a vertical line all the way through your graph at the point where the most precipitate is formed.

  4. Which substance was "in excess" to the left of the vertical line on your graph?  Label your graph accordingly.

  5. Which substance was "in excess" to the right of the vertical line on your graph?  Label your graph accordingly.

  6. For your vertical line, how many moles of potassium iodide were used?

  7. For your vertical line, how many moles of lead nitrate were used?

  8. According to your results, what is the empirical formula for lead iodide?


  9. Write a complete balanced equation for the reaction of potassium iodide with lead nitrate.


[Continuous Variation Lab #2 score sheet][MHS Chem page]