• 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