7.1 Acids and alkalis - PowerPoint PPT Presentation

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7.1 Acids and alkalis

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  1. 13 October 2014 7.1 Acids and alkalis Why are solutions acidic or alkaline? How do we measure acids? Acids Alkalis

  2. 13 October 2014 7.1 Acids and alkalis • Acids are solutions which produce H+ ions when added to water. • Bases are substances which neutralise acids. • Alkalis are soluble bases. They produce OH- ions in water. • The pH scale shows how acidic or alkaline a solution is. Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!

  3. What are acids and bases? • Acids dissolve in water to produce Hydrogen (H+) ions. Hydrochloric Acid has the formula HCl. HCl(g)water H+(aq) + Cl- (aq) What do the terms (g), (s) and (aq) mean? • Alkalis dissolve in water to produce Hydroxide (OH-) ions. Sodium Hydroxide has the formula NaOH. NaOH(s)water Na+(aq) + OH- (aq)

  4. Measuring Acidity • Indicators are chemicals which change colour when added to acids or alkalis. E.g. Litmus, beetroot juice. • pH goes from 0 = strong acid to 14 = strong alkali. Universal indicator shows the whole range.

  5. Which is the most alkaline? • Test a number of substances using universal indicator to find the strongest alkaline. • Record your results in a table with the pH level. P197 Summary questions.

  6. 13 October 2014 7.1 Acids and alkalis • Acids are solutions which produce H+ ions when added to water. • Bases are substances which neutralise acids. • Alkalis are soluble bases. They produce OH- ions in water. • The pH scale shows how acidic or alkaline a solution is. Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!