Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mineral cotunnite.
Structure and properties
In solid PbCl2, each lead ion is coordinated by 9 chloride ions – 6 lie at the apices of a trigonal prism and 3 lie beyond the centers of each prism face. The 9 chloride ions are not equidistant from the central lead atom, 7 lie at 280–309 pm and 2 at 370 pm. PbCl2 forms white orthorhombic needles. While Lead(II) chloride is abundant in many natural water reserves, it is unsafe for human consumption and must be filtered out.
Vaporized PbCl2 molecules have a bent structure with the Cl-Pb-Cl angle being 98° and each Pb-Cl bond distance being 2.44 Å. Such PbCl2 is emitted from internal combustion engines that use ethylene chloride-tetraethyllead additives for antiknock purposes.
The solubility of PbCl2 in water is low (4.5 g/L at 20 °C) and for practical purposes it is considered insoluble. Its solubility product constant (Ksp) is 1.7×10−5. It is one of only four commonly insoluble chlorides, the other three being silver chloride (AgCl) with Ksp = 1.8×10−10, copper(I) chloride (CuCl) with Ksp = 1.72×10−7 and mercury(I) chloride (Hg2Cl2) with Ksp = 1.3×10−18.
PbCl2 occurs naturally in the form of the mineral cotunnite. It is colorless, white, yellow, or green with a density of 5.3–5.8 g/cm3. The hardness on the Mohs scale is 1.5–2. The crystal structure is orthorhombic dipyramidal and the point group is 2/m 2/m 2/m. Each Pb has a coordination number of 9. Cotunnite occurs near volcanoes: Vesuvius, Italy; Tarapacá, Chile; and Tolbachik, Russia.
- Pb(NO3)2(aq) + 2 NaCl(aq) → PbCl2(s) + 2 NaNO3(aq)
- Pb(CH3COO)2(aq) + HCl(aq) → PbCl2(s) + 2 CH3COOH(aq)
- basic PbCO3 + 2 HCl(aq) → PbCl2(s) + CO2(g) + H2O
- Pb(NO3)2(aq) + 2 HCl(aq) → PbCl2(s) + 2 HNO3(aq)
Treatment of lead dioxide with hydrochloric acid gives lead(II) chloride as well as chlorine gas:
Treatment of lead oxide with hydrochloric acid gives lead(II) chloride as well as water
- PbO(s) + 2 HCl → PbCl2(s) + H2O
PbCl2(s) also forms by the action of chlorine gas on lead metal:
- Pb + Cl2 → PbCl2
Addition of chloride ions to a suspension of PbCl2 gives rise to soluble complex ions. In these reactions the additional chloride (or other ligands) break up the chloride bridges that comprise the polymeric framework of solid PbCl2(s).
- PbCl2(s) + Cl- → [PbCl3]-(aq)
- PbCl2(s) + 2 Cl- → [PbCl4]2-(aq)
PbCl2 reacts with molten NaNO2 to give PbO:
- PbCl2(l) + 3 NaNO2 → PbO + NaNO3 + 2 NO + 2 NaCl
PbCl2 is used in synthesis of lead(IV) chloride (PbCl4): Cl2 is bubbled through a saturated solution of PbCl2 in aqueous NH4Cl forming [NH4]2[PbCl6]. The latter is reacted with cold concentrated sulfuric acid (H2SO4) forming PbCl4 as an oil.
Lead(II) chloride is the main precursor for organometallic derivatives of lead, such as plumbocenes. The usual alkylating agents are employed, including Grignard reagents and organolithium compounds:
- 2 PbCl2 + 4 RLi → R4Pb + 4 LiCl + Pb
- 2 PbCl2 + 4 RMgBr → R4Pb + Pb + 4 MgBrCl
- 3 PbCl2 + 6 RMgBr → R3Pb-PbR3 + Pb + 6 MgBrCl
These reactions produce derivatives that are more similar to organosilicon compounds, i.e. that Pb(II) tends to disproportionate upon alkylation.
PbCl2 can be used to produce PbO2 by treating it with sodium hypochlorite (NaClO), forming a reddish-brown precipitate of PbO2.
- Molten PbCl2 is used in the synthesis of lead titanate (PbTiO3) and barium lead titanate ceramics by cation replacement reactions:
- xPbCl2(l) + BaTiO3(s) → Ba1-xPbxTiO3 + xBaCl2
- PbCl2 is used in production of infrared transmitting glass, and ornamental glass called aurene glass. Aurene glass has an iridescent surface formed by spraying with PbCl2 and reheating under controlled conditions. Stannous chloride (SnCl2) is used for the same purpose.
- Pb is used in HCl service even though the PbCl2 formed is slightly soluble in HCl. Addition of 6–25% of antimony (Sb) increases corrosion resistance.
- A basic chloride of lead, PbCl2·Pb(OH)2, is known as Pattinson's white lead and is used as pigment in white paint.
- PbCl2 is an intermediate in refining bismuth (Bi) ore. The ore containing Bi, Pb, and Zn is first treated with molten caustic soda to remove traces of acidic elements such as arsenic and tellurium. This is followed by the Parkes desilverization process to remove any silver and gold present. The ore now contains Bi, Pb, and Zn. It is treated with Cl2 gas at 500 °C. ZnCl2 forms first and is removed. Then PbCl2 forms and is removed leaving pure Bi. BiCl3 would form last.
Like other lead containing compounds, exposure to PbCl2 may cause lead poisoning.
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