Step 1: Recall the relationship between pH and the concentration of hydronium ions ([H₃O⁺]). The formula is: . Rearrange this formula to solve for [H₃O⁺]: .
Step 2: Substitute the given pH value (2.50) into the formula to calculate [H₃O⁺]. This will give the concentration of hydronium ions in moles per liter.
Step 3: Use the relationship between [H₃O⁺] and [OH⁻] in water, which is governed by the ion product constant for water: . At 25°C, . Rearrange this formula to solve for [OH⁻]: .
Step 4: Determine whether the substance is acidic, neutral, or basic based on the pH value. A pH less than 7 indicates an acidic solution, a pH of 7 indicates a neutral solution, and a pH greater than 7 indicates a basic solution. Since the pH is 2.50, the solution is acidic.
Step 5: Complete the table by filling in the calculated values for [H₃O⁺] and [OH⁻], and indicate that the solution is acidic based on the pH value.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pH Scale
The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, while values below 7 indicate acidity and values above 7 indicate basicity. The scale is logarithmic, meaning each whole number change represents a tenfold change in acidity or basicity.
In aqueous solutions, the concentration of hydronium ions (H3O+) and hydroxide ions (OH-) determines the pH. An increase in H3O+ concentration results in a lower pH (more acidic), while an increase in OH- concentration results in a higher pH (more basic). The product of these concentrations is constant at 25°C, known as the ion product of water.
Solutions can be classified as acidic, neutral, or basic based on their pH values. Acidic solutions have a pH less than 7, neutral solutions have a pH of exactly 7, and basic solutions have a pH greater than 7. The classification helps in understanding the chemical behavior and reactivity of substances in different environments.