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Ch.16 - Acids and Bases
Chapter 16, Problem 132

Lakes that have been acidified by acid rain can be neutralized by liming, the addition of limestone (CaCO3). How much limestone (in kg) is required to completely neutralize a 4.3 billion liter lake with a pH of 5.5?

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1
Determine the concentration of hydrogen ions \([H^+]\) in the lake using the pH value: \([H^+] = 10^{-pH}\).
Calculate the total moles of \([H^+]\) in the lake by multiplying the concentration of \([H^+]\) by the volume of the lake in liters.
Write the balanced chemical equation for the neutralization reaction: \(CaCO_3 + 2H^+ \rightarrow Ca^{2+} + CO_2 + H_2O\).
Use stoichiometry to find the moles of \(CaCO_3\) needed, knowing that 1 mole of \(CaCO_3\) neutralizes 2 moles of \(H^+\).
Convert the moles of \(CaCO_3\) to mass in kilograms using the molar mass of \(CaCO_3\) (100.09 g/mol).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pH and Acidity

pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or alkalinity. A pH of 7 is neutral, while values below 7 indicate acidity. In this case, a pH of 5.5 suggests the lake is acidic, which can harm aquatic life. Understanding pH is crucial for determining how much limestone is needed to neutralize the lake.
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Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt, effectively reducing the acidity of the solution. In this scenario, limestone (CaCO3) acts as a base that reacts with the hydrogen ions in the acidic lake water, raising the pH towards neutrality. Knowing the stoichiometry of this reaction is essential for calculating the amount of limestone required.
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Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. To determine how much limestone is needed, one must use the molar mass of CaCO3 and the volume of the lake to find the total moles of hydrogen ions present. This allows for the precise calculation of limestone required to achieve neutralization.
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Related Practice
Textbook Question

The binding of oxygen by hemoglobin in the blood involves the equilibrium reaction: HbH+(aq) + O2(aq) ⇌ HbO2(aq) + H+(aq) In this equation, Hb is hemoglobin. The pH of normal human blood is highly controlled within a range of 7.35 to 7.45. Given the above equilibrium, why is this important? What would happen to the oxygen-carrying capacity of hemoglobin if blood became too acidic (a dangerous condition known as acidosis)?

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Textbook Question

Carbon dioxide dissolves in water according to the equations:

CO2(g) + H2O(l) ⇌ H2CO3(aq)

H2CO3(aq) + H2O(l) ⇌ HCO3(aq) + H3O+(aq)

Carbon dioxide levels in the atmosphere have increased about 20% over the last century. Given that Earth's oceans are exposed to atmospheric carbon dioxide, what effect might the increased CO2 be having on the pH of the world's oceans? What effect might this change be having on the limestone structures (primarily CaCO3) of coral reefs and marine shells?

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Textbook Question

People often take milk of magnesia to reduce the discomfort associated with acid stomach or heartburn. The recommended dose is 1 teaspoon, which contains 4.00×102 mg of Mg(OH)2. What volume of an HCl solution with a pH of 1.3 can be neutralized by one dose of milk of magnesia? If the stomach contains 2.00×102 mL of pH 1.3 solution, is all the acid neutralized? If not, what fraction is neutralized?

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Open Question
Acid rain over the Great Lakes has a pH of about 4.5. Calculate the [H3O+] concentration of this rain and compare that value to the [H3O+] concentration of rain over the West Coast, which has a pH of 5.4. How many times more concentrated is the acid in the rain over the Great Lakes compared to the rain over the West Coast?
Open Question
White wines tend to be more acidic than red wines. Find the [H3O+] concentration in a Sauvignon Blanc with a pH of 3.23 and a Cabernet Sauvignon with a pH of 3.64. How many times more acidic is the Sauvignon Blanc than the Cabernet Sauvignon?
Open Question
Common aspirin is acetylsalicylic acid, which has the structure shown here and a pKa of 3.5. Calculate the pH of a solution in which one normal adult dose of aspirin (6.5 * 10^2 mg) is dissolved in 8.0 ounces of water.