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The differences between strong and weak acids

The differences between strong and weak acids. Hydrochloric acid is a strong acid. Acetic (ethanoic) acid is a weak acid. What are the differences between strong and weak acids?. 1 pH. pH measures the hydrogen ion concentration of the solution.

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The differences between strong and weak acids

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  1. The differences between strong and weak acids

  2. Hydrochloric acid is a strong acid. Acetic (ethanoic) acid is a weak acid. What are the differences between strong and weak acids?

  3. 1 pH pH measures the hydrogen ion concentration of the solution. The greater the pH, the lower [H+].

  4. Universal indicator is added to 1.0 mol L-1 hydrochloric acid (left) and 1.0 mol L-1 acetic acid (right). The hydrochloric acid solution turns red, the acetic acid solution turns orange-red. Hydrochloric Acetic acid acid pH = 0 pH = 2

  5. Both solutions contain the same concentration of acid, but the strong acid has a lower pH. Strong acids contain a greater concentration of hydrogen ions than weak acids.

  6. 2 Electrical conductivity Solutions conduct electricity only if they contain ions which are free to move. The greater the number of ions in solution, the better the electrical conductivity.

  7. Hydrochloric acid is a good conductor of electricity. This light bulb glows brightly. Hydrochloric acid contains a large number of ions in solution.

  8. Acetic acid conducts electricity poorly. The light bulb is not glowing brightly. The acetic acid solution contains comparatively few ions in solution.

  9. Strong acid Weak acid Strong acids contain many ions in solution. Weak acids contain few ions in solution.

  10. Strong acids are fully ionised in solution: HCl(g) + H2O(l) H3O+(aq) + Cl- The normal arrow shows that the reaction goes to completion: every acid molecule reacts with water to form H3O+ and Cl-. Weak acids are only partially ionised in solution: CH3COOH(l) + H2O(l) H3O+(aq) + CH3COO-(aq) The equilibrium arrow shows that the reaction does not go to completion. Only a few of the acid molecules react with water to form ions; the rest remain as CH3COOH molecules.

  11. Rate of reaction with • magnesium ribbon

  12. 1 mol L-1 acetic acid (left) and 1 mol L-1 hydrochloric acid (right) with magnesium ribbon. Both test tubes contained the same volume of acid before equal lengths of magnesium ribbon were added and the bungs put in. The reaction in the right hand tube (HCl) is more rapid.

  13. The HCl (right) is reacting quite vigorously, while the CH3COOH reaction is relatively slow.

  14. The reaction in the right hand tube is now finished, but the left hand (acetic) acid is still bubbling away.

  15. Still going…

  16. Finally, after about 10 minutes, the reaction in the left hand tube is also finished. The total volume of hydrogen gas produced is the same in strong and weak acids, but their reaction rates are different.

  17. 2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g) 2CH3COOH(aq) + Mg(s) → (CH3COO)2Mg(aq) + H2(g) In each case Mg(s) is reacting with H+(aq). The rate of reaction is determined by the concentration of H+ in solution, which is about 100 times greater in the strong acid HCl (pH = 0) than in CH3COOH (pH = 2). The volume of H2 formed is determined by the number of moles of Mg and HCl or CH3COOH. Since the mass of Mg and the concentrations of acids were equal, the volume of H2 formed is the same.

  18. Strong acids are fully ionised. They contain high concentrations of H3O+, have low pHs and react rapidly with magnesium ribbon. Weak acids are only partially ionised. They contain low concentrations of H3O+, have higher pHs and react slowly with magnesium ribbon. Equal volumes of strong and weak acids of the same concentration will react with the same mass of magnesium ribbon because they contain the same amount (number of moles) of acid.

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