IB DP Chemistry: SL复习笔记8.2.8 Comparing Strong & Weak Acids

• Strong and weak acids can be distinguished from each other by their:
  • pH value (using a pH meter or universal indicator)
  • Electrical conductivity
  • Reactivity

pH value

• An acid dissociates into H⁺ in solution according to:

HA → H⁺ + A^-

• The stronger the acid, the greater the concentration of H⁺ and therefore the lower the pH

pH value of a Strong Acid & Weak Acid Table

Electrical conductivity

• Since a stronger acid has a higher concentration of H⁺ it conducts electricity better
• Stronger acids therefore have a greater electrical conductivity
• The electrical conductivity can be determined by using a conductivity meter
• Like the pH meter, the conductivity meter is connected to an electrode
• The conductivity of the solution can be read off the meter

The diagram shows a digital conductivity meter that measures the electrical conductivity of a solution using an electrode

Reactivity

• Strong and weak acids of the same concentrations react differently with reactive metals
• This is because the concentration of H⁺ is greater in strong acids compared to weak acids
• The greater H⁺ concentration means that more H₂ gas is produced in a shorter time

The diagram shows the reaction of 0.1 mol dm^-3 of a strong acid (HCl) with Mg. The reaction produces a lot of bubbles and hydrogen gas due to the high concentration of H⁺ present in solution

The diagram shows the reaction of 0.1 mol dm^-3 of a weak acid (CH₃COOH) with Mg. The reaction produces fewer bubbles of hydrogen gas due to the lower concentration of H⁺ present in solution

• Similar observations would be made in the reaction between strong and weak acids with carbonates and hydrogencarbonates, although the gas given off this time is carbon dioxide
• With oxides and hydroxides, there may not be a lot of visible changes although it is likely that they would dissolve faster in a strong acid than in a weak acid
• These reactions are also likely to produce larger enthalpy changes which could be seen in higher temperature rises