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About half of the hydrochloric acid produced annually in the United States ( 3.0 billion pounds) is used for metal pickling. This process involves the removal of metal oxide layers from metal surfaces to prepare them for coating. (a) Write the overall and net ionic equations for the reaction between iron(III) oxide, which represents the rust layer over iron, and HCl. Identify the Br贸nsted acid and base. (b) Hydrochloric acid is also used to remove scale (which is mostly \(\mathrm{CaCO}_{3}\) ) from water pipes. Hydrochloric acid reacts with calcium carbonate in two stages; the first stage forms the bicarbonate ion, which then reacts further to form carbon dioxide. Write equations for these two stages and for the overall reaction. (c) Hydrochloric acid is used to recover oil from the ground. It dissolves rocks (often \(\mathrm{CaCO}_{3}\) ) so that the oil can flow more easily. In one process, a 15 percent (by mass) HCl solution is injected into an oil well to dissolve the rocks. If the density of the acid solution is \(1.073 \mathrm{~g} / \mathrm{mL},\) what is the \(\mathrm{pH}\) of the solution?

Step by step solution

01

Balance the Overall Reaction for Iron (III) Oxide and HCl

The reaction between iron(III) oxide (Fe鈧侽鈧�) and hydrochloric acid (HCl) produces iron(III) chloride (FeCl鈧�) and water (H鈧侽). The balanced overall reaction is:\[Fe鈧侽鈧� + 6HCl \rightarrow 2FeCl鈧� + 3H鈧侽\]

02

Identify the Br酶nsted Acid and Base

In the reaction of Fe鈧侽鈧� and HCl, HCl acts as the Br酶nsted acid because it donates protons (H鈦�), and Fe鈧侽鈧� is the Br酶nsted base, accepting protons to form water.

03

Write the Net Ionic Equation

The net ionic equation focuses on the species that change during the reaction. For the reaction between Fe鈧侽鈧� and HCl, the net ionic equation is:\[Fe鈧侽鈧� (s) + 6H鈦� (aq) \rightarrow 2Fe鲁鈦� (aq) + 3H鈧侽 (l)\]

04

Write the Equations for Calcium Carbonate Reaction

Calcium carbonate reacts with HCl in two steps:1. \[CaCO鈧� + HCl \rightarrow Ca(HCO鈧�)鈧� + CaCl鈧俓]2. \[Ca(HCO鈧�)鈧� + HCl \rightarrow CO鈧� + H鈧侽 + CaCl鈧俓]The overall reaction is:\[CaCO鈧� + 2HCl \rightarrow CO鈧� + H鈧侽 + CaCl鈧俓]

05

Calculate the Molarity of HCl

To find the molarity of the HCl solution, first calculate the mass of HCl in 1000 mL of solution. Given a 15% by mass solution and a solution density of 1.073 g/mL:\[\text{mass of solution} = 1000 \, \text{mL} \times 1.073 \, \text{g/mL} = 1073 \, \text{g}\]\[\text{mass of } HCl = 1073 \, \text{g} \times 0.15 = 160.95 \, \text{g}\]Convert the mass of HCl to moles using its molar mass (36.46 g/mol):\[\text{moles of } HCl = \frac{160.95 \, \text{g}}{36.46 \, \text{g/mol}} \approx 4.414 \text{ moles}\]Thus, the molarity \([H^+]\) of HCl solution is approximately 4.414 M.

06

Calculate the pH of the HCl Solution

The pH of a solution is calculated using the formula:\[\text{pH} = -\log[H^+]\]For a concentration of 4.414 M, plug it into the equation:\[\text{pH} = -\log(4.414) \approx 0.355\]Thus, the pH of the HCl solution is approximately 0.36.

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Key Concepts

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

Net Ionic Equations

Understanding net ionic equations is crucial for chemistry students. These equations simplify chemical reactions by only showing the components that undergo change. This allows us to clearly see and focus on the core changes occurring during the reaction.

For instance, in the reaction between iron(III) oxide (\(Fe_{2}O_{3}\)) and hydrochloric acid (\(HCl\)), the net ionic equation is:\[ Fe_{2}O_{3} (s) + 6H^+ (aq) \rightarrow 2Fe^{3+} (aq) + 3H_{2}O (l) \]

The net ionic equation strips away the 'spectator ions,' ions that do not participate directly in the reaction. Here, we focus on how oxide ions (\(O^{2-}\)) in rust react with hydrogen ions (\(H^+\)), leading to the formation of water and iron ions (\(Fe^{3+}\)).

When practicing writing net ionic equations, follow these steps:

• Start by writing the balanced molecular equation.
• Identify and separate the strong electrolytes into their individual ions.
• Remove ions that do not change throughout the reaction (spectator ions).

This technique is helpful for recognizing the chemistry happening in transformations, like metal pickling.

Bronsted Acids and Bases

The Br酶nsted-Lowry model of acids and bases is essential to understand chemical reactions involving proton transfer. This theory defines acids as proton donors and bases as proton acceptors.

Using the reaction of iron(III) oxide and HCl again, we can see how this model applies. Hydrochloric acid (HCl) donates protons (\(H^+\)) and is therefore a Br酶nsted-Lowry acid. Meanwhile, iron(III) oxide (\(Fe_{2}O_{3}\)), accepts these protons, acting as a Br酶nsted-Lowry base. This reaction results in the formation of water and iron(III) ions.

Here are a few tips to help identify Br酶nsted acids and bases:

• Look for substances that start with hydrogen or that release hydrogen ions into the solution (typical of acids).
• Bases usually have a lone pair of electrons that can accept protons.

Through this mechanism of exchange, you can see how acids and bases activate changes within a solution, which is a key feature in many chemical processes.

pH Calculation

Calculating the pH of a solution is a fundamental skill in chemistry. It helps in determining how acidic or basic a solution is, which is essential for understanding the chemical environment.

The pH scale normally ranges from 0 to 14. It is calculated using the formula:\[ \text{pH} = -\log[H^+] \]For example, with a hydrochloric acid (HCl) solution having a concentration of 4.414 M, the pH can be determined as:\[ \text{pH} = -\log(4.414) \approx 0.36 \]

These are the steps to calculate pH:

• Find the concentration of hydrogen ions (\[H^+\]) in the solution.
• Use the pH formula to convert this concentration into a pH value.
• Interpret the pH value: a pH less than 7 denotes an acidic solution, pH of 7 is neutral, and above 7 is basic.

Through pH calculations, gains insights can be acquired on how chemical reactions might behave, and help balance equations accurately within practical scenarios like industrial metal treatment.