An Experiment to Determine the Empirical Formula of Lead Iodide

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An Experiment to Determine the Empirical Formula of Lead Iodide


        The empirical formula shows the simplest whole number of ratio of atoms of each element in a molecule of a compound.

In this experiment, we will determine the empirical formula of lead iodide. An insoluble lead iodide compound is formed by dissolving the lead in nitric acid and reacting with potassium iodide. Then, the lead iodide is filtered and dried for a week. In the end of the experiment, the mass of lead, filter papers and filter paper with lead iodide are recorded.

The ratio of moles of lead to moles of iodine in the compound can be obtained either by weighing/calculating the mass of each element from the experiment raw data. In order to get the mass of iodide in the lead iodide compound, we can calculate by deducting the initial mass of lead from the mass of the precipitate. By knowing the mass of each element, we can determine the amount of each element (moles) than the ratio of the compound.




30 cm3 3M HNO3 ; distilled water ;  1.2g potassium iodide (KI)


Amount of Lead (Pb)


Amount of lead iodide formed

Method for controlling variables:

Glassware, electronic balance



  • 3 x 250 cm3 beaker
  • 1 x 150 cm3 beaker
  • 3 x watch glass
  • 1 x Electronic balance (300 g, readability ±0.001 g)
  • 3 x cartridge burner
  • 3 x iron stand
  • 1 x 50 cm3 graduated cylinder (1 cm3 graduation ± 0.5cm3)
  • 3 x filter paper
  • 3 x long-stemmed funnel
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  • Distilled water
  • Granulated lead
  • 3M HNO3 (nitric acid)
  • Potassium iodide, KI


  1. About 0.130 and 0.150 g of granulated lead was weighed accurately on the electronic balance in a  250 cm3 beaker marked #1. and the mass of  lead was recorded to the nearest 0.001g
  2. The process (1) was repeated with two other beakers marked #2 and #3.
  3. Approximately 30 cm3 of 3 mol dm-3 nitric acid solution (HNO3) was placed in a 50 cm3 graduated cylinder.
  4. 1/3 (10cm3) of 3 mol dm-3 nitric acid was poured onto each ...

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