Textbook Question
The following data were collected for the desturction of O3 by H (O3 + H → O2 + OH) at very low concentrations (b) Calculate the rate constant
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Ch.18 - Chemistry of the Environment
Chapter 18, Problem 90a
The precipitation of Al(OH)3 (Ksp) = 1.3⨉10-33) is sometimes used ot purify water. (a) Estimate the pH at which precipitation of Al(OH)3 will begin if 5.0 lb of Al2(SO4)3 is added to 2000 gal of water
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Convert the mass of Al_2(SO_4)_3 from pounds to grams using the conversion factor 1 lb = 453.592 g.
Calculate the number of moles of Al_2(SO_4)_3 using its molar mass (Al_2(SO_4)_3 has a molar mass of approximately 342.15 g/mol).
Determine the concentration of Al^3+ ions in the solution by dividing the moles of Al_2(SO_4)_3 by the volume of water in liters (1 gal = 3.78541 L).
Use the K_sp expression for Al(OH)_3, which is K_sp = [Al^3+][OH^-]^3, to find the concentration of OH^- needed for precipitation.
Convert the concentration of OH^- to pH using the relation pH + pOH = 14, where pOH = -log[OH^-].
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Solubility Product Constant (Ksp)
The solubility product constant (Ksp) is an equilibrium constant that applies to the solubility of sparingly soluble ionic compounds. It represents the maximum concentration of ions in a saturated solution at a given temperature. For Al(OH)3, Ksp = 1.3 × 10^-33 indicates that the compound is very insoluble, meaning that only a tiny amount can dissolve in water before precipitation occurs.
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Solubility Product Constant
pH and Hydroxide Ion Concentration
pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. In the context of Al(OH)3 precipitation, the pH must be sufficiently high to increase the concentration of hydroxide ions (OH-) in the solution. As the pH rises, the solubility of Al(OH)3 decreases, leading to precipitation when the product of the ion concentrations exceeds Ksp.
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06:12Hydroxide Ion Concentration Example
Stoichiometry and Dilution
Stoichiometry involves the calculation of reactants and products in chemical reactions, while dilution refers to the process of reducing the concentration of a solute in a solution. In this question, understanding how to convert the mass of Al2(SO4)3 added to water into moles and then into hydroxide ion concentration is crucial for estimating the pH at which Al(OH)3 will begin to precipitate.
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Related Practice
Open Question
The degradation of CF3CH2F (an HFC) by OH radicals in the troposphere is first order in each reactant and has a rate constant of k = 1.6x10^8 M-1s-1 at 4 °C. If the tropospheric concentrations of OH and CF3CH2F are 8.1x10^5 and 6.3x10^8 molecules/cm3, respectively, what is the reaction rate at this temperature in M/s?
Textbook Question
The Henry's law constant for CO2 in water at 25 °C is 3.1x10^-2 M atm-1. (a) What is the soubility of CO2 in water at this temperature if the soltuion is in contact with air at normal atmospheric pressure?
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Textbook Question
The valuable polymer polyurethane is made by a condensa- tion reaction of alcohols (ROH) with compounds that con- tain an isocyanate group (RNCO). Two reactions that can generate a urethane monomer are shown here: (i)
(ii)
(c) If you wanted to promote the formation of the isocyanate intermediate in each reaction, what could you do, using Le Châtelier's principle?
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Textbook Question
The pH of a particular raindrop is 5.6.
(a) Assuming the major species in the raindrop are H2CO3(aq), HCO3-(aq) and CO32- (aq), Calculate the concentrations of these species in the raindrop, assuming the total carbonate concentration is 1.0 * 10-5 M. The appropriate Ka values are given in Table 16.3.
(b) What experiments could you do to test the hypothesis that the rain also contains sulfur-containing species that contribute to its pH? Assume you have a large sample of rain to test.
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Textbook Question
The pH of a particular raindrop is 5.6. (b) What experiments could you do to test the hypothesis that the rain also contains sulfur-containing species that contribute to its pH? Assume you have a large sample of rain to test.
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