Problem 43 - Chemistry: The Central Science

Question

(a) What is a strong acid? (b) A solution is labeled \(0.500 \mathrm{M} \mathrm{HCl}\). What is \(\left[\mathrm{H}^{+}\right]\) for the solution? (c) Which of the following are strong acids: \(\mathrm{HF}, \mathrm{HCl}, \mathrm{HBr}, \mathrm{HI}\) ?

Step-by-Step Solution

Answer

(a) A strong acid is an acid that ionizes completely in an aqueous solution, donating all its protons (\(\mathrm{H}^{+}\)) to the surrounding water molecules and resulting in a high concentration of \(\mathrm{H}^{+}\) ions. (b) For the \(0.500 \mathrm{M}\ \mathrm{HCl}\) solution, \(\left[\mathrm{H}^{+}\right] = 0.500 \mathrm{M}\) as \(\mathrm{HCl}\) ionizes completely in water. (c) The strong acids among the given list are \(\mathrm{HCl}, \mathrm{HBr}\), and \(\mathrm{HI}\).

Step 1: Definition of a Strong Acid

A strong acid is a type of acid that ionizes (dissociates) completely in an aqueous solution, meaning it donates all of its protons (\(\mathrm{H}^{+}\)) to the surrounding water molecules. This also results in a high concentration of \(\mathrm{H}^{+}\) ions, making the solution highly acidic.

Step 2: Calculating \(\mathrm{H}^{+}\) Concentration in \(\mathrm{HCl}\) Solution

Given that the solution is labeled as \(0.500 \mathrm{M}\ \mathrm{HCl}\), we can find the concentration of \(\mathrm{H}^{+}\) ions. Since \(\mathrm{HCl}\) is a strong acid, it ionizes completely in water. Thus, the concentration of \(\mathrm{H}^{+}\) ions will be equal to the concentration of \(\mathrm{HCl}\) in the solution. So, \(\left[\mathrm{H}^{+}\right] = 0.500 \mathrm{M}\).

Step 3: Identifying Strong Acids

Among the given list of acids, \(\mathrm{HF}, \mathrm{HCl}, \mathrm{HBr}, \mathrm{HI}\), we need to identify the strong acids. A helpful rule to remember is that hydrogen halides (acids formed when hydrogen combines with a halogen) are generally strong acids, with the exception of \(\mathrm{HF}\). Thus, the strong acids in this list are \(\mathrm{HCl}, \mathrm{HBr}\), and \(\mathrm{HI}\).

Key Concepts

Acid Ionization

When we talk about acid ionization, we refer to the process where an acid breaks down in water, releasing hydrogen ions ( H^{+}) into the solution. This reaction is crucial because it determines how acidic the solution becomes. One important element of ionization is whether the acid is strong or weak.

• Strong Acid: Completely ionizes in water, releasing all available hydrogen ions. This means that the concentration of hydrogen ions is equal to the starting concentration of the acid.
• Weak Acid: Only partially ionizes, meaning not all the hydrogen ions are released. This results in a lower concentration of hydrogen ions compared to the initial acid concentration.

A strong acid, like hydrochloric acid (HCl), instantly dissociates in water, making it a prime example of complete ionization. This complete ionization contributes to strong acids' characteristic properties, such as high conductivity and low pH values.

Hydrogen Ions Concentration

Hydrogen ions concentration is an essential topic when discussing acids. The concentration of H^{+} ions in a solution indicates its acidity level. The higher the concentration of these ions, the more acidic the solution is. To find this concentration, especially in solutions of strong acids, you often simply look at the molarity of the acid solution. For instance, if you have a 0.500 M HCl solution: - Since HCl is a strong acid, it dissociates completely. - This means the concentration of hydrogen ions, [H^{+}], will also be 0.500 M. Understanding the hydrogen ions concentration allows you to determine the acid strength, predict the reaction’s behavior, and calculate the pH of the solution. Since the concentration [H^{+}] can directly predict how an acid will act in a chemical reaction, it is crucial for solving many chemistry problems.

Hydrogen Halides

Hydrogen halides are compounds formed when hydrogen combines with halogen elements on the periodic table, like fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These compounds can become acids when mixed with water, known as hydrohalic acids. Key Points About Hydrogen Halides:

• Nature of Compounds: These are often gaseous and become acidic when dissolved in water.
• Strength of Acids: Most hydrogen halides, such as HCl, HBr, and HI, are considered strong acids. These ionize completely in water, exhibiting strong acidic behavior.
• Exception: HF (hydrogen fluoride) is an exception, as it is a weak acid. Unlike its counterparts, it only partially ionizes in solution.

The understanding of hydrogen halides is crucial because they illustrate how the bond strength and polarity affect the acid's behavior in a solution. Knowing which hydrogen halides are strong acids helps predict their behavior in reactions and informs safe handling practices.