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Precipitate Formation: Formation of Lead (II) Iodide

Precipitate Formation: Formation of Lead (II) Iodide. When mixed, two clear solutions produce a dense yellow precipitate. Purpose. To observe the formation of a precipitate from ionic compounds in an aqueous state. Demonstration. The formation of PbI 2(s) from Pb(NO 3 ) 2 and 2KI solutions.

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Precipitate Formation: Formation of Lead (II) Iodide

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  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. 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) Double Replacement Reactions

  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 andKI 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.

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