Limestone is composed primarily of calcium carbonate, A \(1.0-\mathrm{mm}^{3}\) chip of limestone was accidentally dropped into a water-filled swimming pool, measuring \(10 \mathrm{~m} \times 7 \mathrm{~m} \times 2 \mathrm{~m}\). Assuming that the carbonate ion does not function as a Bronsted base and that the \(\mathrm{pH}\) of the water is 7 , will the pebble dissolve entirely? The density of calcium carbonate is \(2.71 \mathrm{~g} \cdot \mathrm{cm}^{-3}\).

Short Answer

Expert verified
Considering the low solubility of calcium carbonate in neutral pH conditions and the large volume of water in the pool, the limestone pebble will not dissolve entirely.

Step by step solution

01

Calculate the mass of the limestone chip

Determine the mass of the limestone chip using its volume and the density of calcium carbonate. The volume of the chip is given as 1.0 mm³, which is equivalent to 0.001 cm³ since \(1 \text{mm}^3 = 0.001 \text{cm}^3\). The density of calcium carbonate is 2.71 g/cm³. The mass (m) is calculated by the formula: \[m = \text{density} \times \text{volume}\] Thus, \[m = 2.71 \text{g/cm}^3 \times 0.001 \text{cm}^3\]
02

Dissolution of calcium carbonate

Consider the solubility of calcium carbonate in water. The pH of the water in the pool is 7, which is neutral, meaning it is neither acidic nor basic. Since it is assumed that the carbonate ion does not act as a Bronsted base, the pH of the water will not change due to the addition of limestone. Calcium carbonate is only slightly soluble in water, and its solubility is even lower in neutral to alkaline conditions. Given the neutral pH, we can infer that the calcium carbonate will not dissolve much.
03

Consider the size of the pool

The volume of the swimming pool can be calculated using its dimensions. However, because the size of the pool is vastly larger than the size of the limestone chip, and the solubility of calcium carbonate is low, the relative amount of water is large enough that it won't be saturated with calcium carbonate from just a single chip. This implies that the entirety of the chip is unlikely to dissolve.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Calcium Carbonate Solubility
Calcium carbonate ((CaCO_3)) is an ionic compound widely found in geological formations such as limestone and chalk, and also in organisms like mollusks and corals. Solubility is an important property that dictates how much of this compound can dissolve in water. Calcium carbonate is considered to be only slightly soluble in water, meaning that only a small amount of this compound can be dissolved at a given time under standard conditions.

{(CaCO_3 (s) ↔ Ca^{2+} (aq) + CO_3^{2-} (aq))}
The solubility is often expressed as the solubility product constant ((K_{sp})), which for calcium carbonate at room temperature is approximately 3.3 x 10^{-9}, a low value reflecting its limited solubility. This equilibrium process is influenced by various factors, such as temperature and the presence of other ions in solution.

In the context of the educational problem, the mass of a 1.0 mm³ limestone chip can be calculated, but when it comes to dissolving in a large body of water like a swimming pool, calcium carbonate's low solubility means that it is unlikely the chip will dissolve entirely. When students tackle homework involving solubility, understanding the concept of solubility product and the equilibrium process is essential for explaining the behavior of such sparingly soluble compounds in water.
Bronsted Base Theory
The Bronsted-Lowry theory defines an acid as a substance that can donate a proton ((H^+)), while a base is a substance that can accept a proton. This theory expands the definition of acids and bases beyond those simply containing hydrogen or hydroxide ions.

For instance, in aqueous solutions, water can act as both a Bronsted acid and a Bronsted base. This dual behavior is fundamental to many chemical reactions in water. When a substance like calcium carbonate is introduced to water, we'd consider whether the carbonate ion ((CO_3^{2-})) could act as a Bronsted base and thus alter the water's pH. In the textbook exercise, it is assumed that the carbonate ion does not act as a Bronsted base; if it did, it would accept a proton and potentially change the pH value by forming bicarbonate ((HCO_3^-)).

Understanding this aspect of the Bronsted base theory is crucial to determining the subsequent chemical reactions that might influence solubility and the pH of the solution. In the given scenario, assuming that the carbonate ion doesn't behave as a base simplifies the problem by eliminating the need to consider changes in pH due to the dissolution of the limestone chip.
pH and Solubility Relationships
The pH of a solution is a measure of its acidity or basicity, which in turn can impact the solubility of certain compounds. For calcium carbonate, pH plays a critical role. As a rule of thumb, the solubility of calcium carbonate decreases as the pH of the solution increases, meaning it is less soluble in more alkaline conditions. Conversely, in an acidic environment, increased solubility is observed because the excess (H^+) ions react with the carbonate ions to form bicarbonate, which is more soluble.

In a neutral pH of 7, like the water in the swimming pool from our exercise, calcium carbonate has a very low solubility. No additional protons are available from the water to react with (CO_3^{2-}), and consequently, there's little to no increase in solubility that would result from a decrease in pH. It is, therefore, pretty safe to conclude that, with a neutral pH and a carbonate ion not acting as a Bronsted base, the limestone chip in the exercise would not completely dissolve in the pool's large volume of water.

Students learning about solubility should consider how pH affects ionic compounds like calcium carbonate. This is not only crucial for chemistry and environmental science courses but also for practical situations, such as understanding water quality and treatment processes in real-life applications.

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Most popular questions from this chapter

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(a) What must be the ratio of the concentrations of \(\mathrm{CO}_{3}{ }^{2-}\) and \(\mathrm{HCO}_{3}{ }^{-}\)ions in a buffer solution having a \(\mathrm{pH}\) of \(11 . \mathrm{O}\) ? (b) What mass of \(\mathrm{K}_{2} \mathrm{CO}_{3}\) must be added to \(1.00 \mathrm{~L}\) of \(0.100 \mathrm{M} \mathrm{KHCO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ? (c) What mass of \(\mathrm{KHCO}_{3}\) must be added to \(1.00 \mathrm{~L}\) of \(0.100 \mathrm{M} \mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ? (d) What volume of \(0.200 \mathrm{M} \mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) must be added to \(100 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{KHCO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ?

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