Acid-base equilibria

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The equilibrium law helps to make sense of the behaviour of acids and bases. The theory helps to account for the behaviour of strong and weak acids as well as explaining the the way that indicators and buffer solutions work.

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Tutorials

• Sorted FAQs on Acid-Base equilibria
• Ionisation constants for acids: audio tutorial
• Is calcium hydroxide a strong or a weak base?

Webguides

• Indicator colour changes
• The pH of solutions of sulphuric acid
• Key ideas about acid-base equilibria

Recently Asked Questions

• When hydrochloric acid is titrated against a solution containing sodium hydrogencarbonate and sodium carbonate, the reaction takes place in 2 stages: Stage 1: Na₂CO₃ + HCl ---> NaHCO₃ + NaCl and the colour change of phenolphthalein indicates the end point Stage 2: NaHCO₃ + HCl---> NaCl + H₂O + CO₂ (some NaHCO₃ is originally present in the mixture while some is converted from Na₂CO₃) and the colour change of methyl orange indicates the end point. I wonder why all of the Na₂CO₃ must convert to NaHCO₃ before the reaction between NaHCO₃ and HCl starts - in other words, why don't Na₂ CO₃ and NaHCO₃react with HCl together? 280410
• When hydrochloric acid and aqueous ammonia react with water, the following reactions occur : HCl(aq) + H₂O(l) --> H₃O⁺(aq) + Cl^-(aq) and NH₃(aq) + H₂O(l) --> NH₄⁺(aq) + OH^-(aq). What happens when it is gaseous hydrogen chloride and gaseous ammonia that is reacting with water? Do the state symbols of the products change? 280410
• Does the pH of a weak acid increase upon dilution or does it remain the same? 280410

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Tests

• Acid-base equilibria (A2)

updated: 09 July 2003