Praxis Chemistry Acids Bases and pH Scale Quiz

pH is calculated using the formula pH = -log[H⁺]. For a hydrogen ion concentration of 1 × 10⁻⁵ M, the calculation is pH = -log(1 × 10⁻⁵) = 5. This indicates that the solution is slightly acidic, as lower pH values correspond to higher acidity.

Hydrochloric acid is classified as a strong acid because it completely dissociates in water, releasing a high concentration of hydrogen ions (H⁺). This characteristic leads to a low pH and strong acidic properties, unlike acetic acid, carbonic acid, and hydrofluoric acid, which are weak acids that do not fully dissociate.

A solution with a pH of 8 is considered basic because it has a higher concentration of hydroxide ions (OH⁻) compared to hydrogen ions (H⁺). The pH scale ranges from 0 to 14, with values above 7 indicating basicity. Therefore, a pH of 8 signifies an alkaline solution.

According to Brønsted-Lowry theory, an acid is defined as a substance that can donate a proton (H⁺) to another substance in a chemical reaction. This theory emphasizes the role of protons in acid-base reactions, distinguishing acids from bases, which are proton acceptors. Thus, the term "donor" accurately describes the function of an acid.

The conjugate base of a species is formed by removing a proton (H⁺) from it. When bicarbonate (HCO₃⁻) loses a proton, it transforms into carbonate (CO₃²⁻). Thus, CO₃²⁻ is the species that results from the deprotonation of HCO₃⁻, making it its conjugate base.

A strong base completely dissociates in water, meaning it breaks down entirely into its constituent ions without any remaining undissociated molecules. This complete ionization results in a solution that contains only ions, confirming that it is 100% ionized.

A buffer solution maintains a stable pH by containing a weak acid and its conjugate base. When an acid or base is added, the weak acid can neutralize excess base, while the conjugate base can neutralize excess acid. This equilibrium helps to minimize changes in pH, allowing the solution to resist fluctuations.

A neutral solution at 25°C has a pH of 7, which indicates that the concentration of hydrogen ions (H⁺) is equal to that of hydroxide ions (OH⁻). This balance defines neutrality, distinguishing it from acidic (pH 7) solutions.

A solution's acidity is measured by its pH level, where lower pH values indicate higher acidity. A pH of 3 means there is a higher concentration of hydrogen ions compared to a pH of 5. Therefore, the solution with pH 3 is indeed more acidic than the one with pH 5.

A conjugate acid-base pair consists of two species that differ by one proton. In this case, NH₃ (ammonia) can accept a proton to become NH₄⁺ (ammonium), making them a conjugate acid-base pair. The other options do not represent such a relationship.

At 25°C, the ion product of water (Kw) is 1 × 10⁻¹⁴, indicating that the concentrations of hydrogen ions [H⁺] and hydroxide ions [OH⁻] are both 1 × 10⁻⁷ M in pure water. This equal concentration results in a neutral pH of 7, as pH is defined as the negative logarithm of [H⁺].

pOH and pH are related through the equation pH + pOH = 14. If the pH of a solution is 6, you can find the pOH by subtracting the pH from 14: pOH = 14 - pH = 14 - 6 = 8. Thus, the pOH of the solution is 8.