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Acidic, basic and neutral salts. Salts Salts are formed when acids react with bases. acid + base → salt + water When strong acids react with strong bases.

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Presentation on theme: "Acidic, basic and neutral salts. Salts Salts are formed when acids react with bases. acid + base → salt + water When strong acids react with strong bases."— Presentation transcript:

1 Acidic, basic and neutral salts

2 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…

3 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).

4 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.

5 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.

6 As it dissolves the colour of the universal indicator changes. The final solution has a pH of about 8.5. WaterSodium ethanoate

7 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)

8 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.

9 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)

10 NH 4 Cl pH = 5 NaCl pH = 7 CH 3 COONa pH = 8.5 Learn these compounds and these pHs.


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