Precipitate%20Formation:%20Formation%20of%20Lead%20(II)%20Iodide

1
Precipitate Formation Formation of Lead (II)
Iodide

• When mixed, two clear solutions produce a dense
  yellow precipitate

2
Purpose

• To observe the formation of a precipitate from
  ionic compounds in an aqueous state.

3
Demonstration

• The formation of PbI2(s) from Pb(NO3)2 and 2KI
  solutions.

Pb2- NO3-
K I-
NO3-

K
PbI2(s)
4
Concepts

• Double Replacement Reactions
• Solubility
• Precipitates

5
Double Replacement Reactions

• Occur when the elements in a solution of reacting
  compounds exchange places, or replace one
  another.
• AB CD ? AD CB
• For this demonstration
• Pb(NO3)2(aq) 2KI(aq) ? PbI2(s)
  2KNO3(aq)

6
Solubility

• Salts are substances composed of ions many salts
  are soluble in water
• Solubility is the amount of a substance needed to
  make a saturated solution at a specific
  temperature.
• Solubility of solids and liquids varies widely,
  for example
• 35.7g of NaCl dissolves in 100mL of H2O, but
  only 0.044g of PbI2 dissolves in 100mL of H2O

7
Solubility

• Solubility is temperature dependent.
• For gases, an increase in temperature will
  decrease the amount of gas that can dissolve
• For salts, the amount and rate of dissolving will
  increase as temperature increases

Amount Rate of Dissolving of Salt
Temperature
8
Precipitates

• A precipitate is an insoluble solid formed when
  two ionic solutions react.
• Pb(NO3)2 and KI are ionic compounds that
  dissociate into ions as they dissolve in water,
  but when mixed together, undergo a double
  replacement reaction to form an insoluble yellow
  precipitate, PbI2.
• Sometimes a downward arrow behind a compound is
  used to indicate that the compound is insoluble
  sometimes the letter s in parentheses for
  solid is used
• PbI2 (s) or PbI2
• Both mean precipitate

9
Conclusions

• Soluble ionic compounds dissociate into water and
  when allowed to react, may produce an insoluble
  compound known as a precipitate.
• If a precipitate is produced, the reaction that
  occurs is known as a double replacement reaction.