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Ch.17 - Additional Aspects of Aqueous Equilibria
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.17 - Additional Aspects of Aqueous EquilibriaProblema 97d
Capitolo 17, Problema 97d

Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?

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Step 1: Write the dissolution equation for lead(II) carbonate: PbCO_3(s) \(\rightleftharpoons\) Pb^{2+}(aq) + CO_3^{2-}(aq).
Step 2: Use the solubility product constant (K_{sp}) for PbCO_3 to express the equilibrium concentrations of the ions. The K_{sp} expression is K_{sp} = [Pb^{2+}][CO_3^{2-}].
Step 3: Assume the solubility of PbCO_3 is 's' mol/L. At equilibrium, [Pb^{2+}] = s and [CO_3^{2-}] = s. Substitute these into the K_{sp} expression to solve for 's'.
Step 4: Convert the solubility 's' from mol/L to ppb (parts per billion) for lead ions. Use the molar mass of lead to convert moles to grams, and then convert grams to ppb.
Step 5: Compare the calculated ppb of lead ions in the saturated solution to the EPA threshold of 15 ppb to determine if the solution exceeds the limit.

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Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is a numerical value that represents the extent to which a compound can dissolve in water. For lead(II) carbonate, PbCO3, Ksp can be used to determine the concentration of lead ions in a saturated solution. If the concentration of lead ions exceeds the EPA limit of 15 ppb, the solution is considered unsafe.
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Solubility Product Constant

Lead(II) Carbonate Dissociation

Lead(II) carbonate dissociates in water to produce lead ions (Pb²⁺) and carbonate ions (CO3²⁻). The equilibrium established during this dissociation is crucial for calculating the concentration of lead ions in a saturated solution. Understanding this dissociation helps in assessing whether the lead concentration surpasses regulatory limits.
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Percent Dissociation Example

Parts Per Billion (ppb)

Parts per billion (ppb) is a unit of measurement used to express very dilute concentrations of substances. In the context of water quality, it indicates the number of parts of a substance per billion parts of water. The EPA's threshold of 15 ppb for lead ions is critical for determining the safety of drinking water, making it essential to compare the calculated lead concentration against this standard.
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Parts per Billion (ppb)
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