Question

Is each of the following statements true or false? (a) All strong acids contain one or more H atoms. (b) A strong acid is a strong electrolyte. (c) A 1.0-M solution of a strong acid will have \(\mathrm{pH}=1.0\)

Short answer

(a) True: Strong acids must contain one or more H atoms to donate as protons (H+) in a solution. (b) True: Strong acids are strong electrolytes, as they fully ionize in a solution, releasing all of their protons as H3O+ ions. (c) False: A 1.0-M solution of a strong acid will have a pH of 0, not 1.0, as \(\mathrm{pH} = -\log_{10}(1) = 0\).

Step-by-step solution

Statement (a): All strong acids contain one or more H atoms.

For an acid to behave as an acid, it has to donate a proton (H+) in a solution. Therefore, a strong acid must contain one or more H atoms to be able to donate them. Hence, statement (a) is true.

Statement (b): A strong acid is a strong electrolyte.

When an acid dissolves in water, it donates protons (H+) to the solution, creating hydronium ions (H3O+). A strong acid completely ionizes in water, releasing all of its protons as H3O+ ions. This would increase the conductivity of the solution, as more ions would be available to carry electrical charge. A strong electrolyte is a substance that completely dissociates into ions when dissolved in water. Since strong acids fully ionize in a solution, they are strong electrolytes. Therefore, statement (b) is true.

Statement (c): A 1.0-M solution of a strong acid will have \(\mathrm{pH}=1.0\).

The pH of a solution is calculated using the equation \(\mathrm{pH} = -\log_{10}[\mathrm{H^{+}}]\), where \([\mathrm{H^{+}}]\) represents the concentration of H+ ions in the solution. In a 1.0-M solution of a strong acid, the concentration of H+ ions will be 1.0 M, since the strong acid completely ionizes in water. Plugging the value into the pH equation, we get:\[\mathrm{pH} = -\log_{10}(1) = 0\] Therefore, a 1.0-M solution of a strong acid will have a pH of 0, not 1.0. So, statement (c) is false.

Key concepts

Electrolytes

Electrolytes are substances that, when dissolved in water, form a solution that can conduct electricity. This occurs because the dissolved electrolytes dissociate into ions, charged particles that move freely in the solution and carry electrical current.

There are two main types of electrolytes:

• Strong electrolytes: These include strong acids, strong bases, and salts. They completely break apart into ions in solutions, which highly enhances the solution's conductivity.
• Weak electrolytes: These only partially dissociate into ions in solution, resulting in limited conductivity.

Strong acids are strong electrolytes because they completely ionize in water, releasing all available H+ ions. This means they have a high ion concentration, leading to greater electrical conductivity. For instance, hydrochloric acid (HCl) is a strong acid that dissociates completely in solution into H+ and Cl- ions, thus acting as a strong electrolyte.

pH Calculation

Calculating the pH of a solution is an essential skill in chemistry. The pH scale is a measure of hydrogen ion \([H^+]\) concentration in a solution, determining its acidity or basicity. The pH value is calculated using the formula: \[\mathrm{pH} = -\log_{10}[\mathrm{H^{+}}]\] Here, the concentration of hydrogen ions \([H^+]\) is measured in moles per liter (Molarity).

In the case of a strong acid, because it dissociates fully in water, the concentration of hydrogen ions \([H^+]\) is equal to the initial concentration of the acid. For example, in a 1.0-M solution of a strong acid like hydrochloric acid (HCl), \([H^+]\) is 1.0 M. By substituting into the formula, \[\mathrm{pH} = -\log_{10}(1) = 0\] Therefore, a 1.0-M solution reflects a pH of 0, not 1.0, indicating a very acidic solution. Remember, the lower the pH, the more acidic the solution.

Proton Donor

The concept of a proton donor is central to understanding acids and their behavior in chemical reactions. An acid's ability to donate protons \(H^+\) to a solution is what defines it as an acid.

• Protons are simply hydrogen ions, denoted as \(H^+\), which have lost their unique electron.
• Strong acids such as sulfuric acid (H2SO4) or nitric acid (HNO3) donate protons readily and completely when dissolved in water.

When an acid dissolves in water, it releases protons into the solution. For example, when hydrochloric acid (HCl) dissociates in water, it donates an H+ ion, forming H3O+, also called a hydronium ion. This donation of protons is vital for many reactions, particularly in biochemistry and industrial chemistry. Understanding proton donation helps explain not only the behavior of acids but also the pH changes in solutions and the conductivity associated with strong electrolytes.