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Published byWalter Jefferson Modified over 9 years ago
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Acidic, basic and neutral salts
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Salts Salts are formed when acids react with bases. acid + base → salt + water When strong acids react with strong bases they neutralise each other, because the salts formed are neutral. The salts of weak acids or weak bases are not neutral though…
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Pure water has a pH of 7. It turns universal indicator green. Sodium chloride is the salt formed when hydrochloric acid (a strong acid) reacts with sodium hydroxide (a strong base).
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Add salt to water……and stir. The solution remains neutral. When NaCl dissolves in water the ionic crystal breaks up, the ions separate and become surrounded by water molecules: NaCl(s) → Na + (aq) + Cl - (aq) Since the pH of the water remains neutral, we know that neither Na + nor Cl - react with water.
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Sodium ethanoate (sodium acetate, CH 3 COONa), is formed when ethanoic acid (a weak acid) reacts with sodium hydroxide (a strong base). Sodium ethanoate is added to water.
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As it dissolves the colour of the universal indicator changes. The final solution has a pH of about 8.5. WaterSodium ethanoate
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Sodium ethanoate is an ionic compound. When it dissolves in water the ions separate and become surrounded by water molecules: CH 3 COONa(s) → CH 3 COO - (aq) + Na + (aq) One of these ions reacts with water to form OH -. Since we know Na + does not react with water, it must be CH 3 COO - : CH 3 COO - (aq) + H 2 O(l) OH - (aq) + CH 3 COOH(aq) The salt of a weak acid and a strong base is basic. Another basic salt you should remember from Year 12 is sodium carbonate: Na 2 CO 3 (s) → 2Na + (aq) + CO 3 2– (aq) CO 3 2– (aq) + H 2 O(l) HCO 3 – (aq) + OH – (aq)
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Ammonium chloride is formed when HCl (a strong acid) reacts with ammonia, NH 3, which is a weak base. When solid ammonium chloride is added to water the pH drops to about 5.
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The ammonium ion reacts with water to form H 3 O + : NH 4 Cl(s) → NH 4 + (aq) + Cl - (aq) The salt of a strong acid and a weak base is acidic. NH 4 + (aq) + H 2 O(aq) H 3 O + (aq) + NH 3 (aq)
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NH 4 Cl pH = 5 NaCl pH = 7 CH 3 COONa pH = 8.5 Learn these compounds and these pHs.
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