Chemistry_Grade_10-12 (1).pdf

Exercise acids and bases 1 in the following reactions

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Exercise: Acids and bases 1. In the following reactions, identify (1) the acid and the base in the reactants and (2) the salt in the product. (a) H 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O (b) CuO + H 2 SO 4 CuSO 4 + H 2 O (c) H 2 O + C 6 H 5 OH H 3 O + + C 6 H 5 O (d) HBr + C 5 H 5 N (C 5 H 5 NH + )Br 2. In each of the following reactions, label the conjugate acid-base pairs. (a) H 2 SO 4 + H 2 O H 3 O + + HSO 4 (b) NH + 4 + F HF + NH 3 (c) H 2 O + CH 3 COO CH 3 COOH + OH (d) H 2 SO 4 + Cl HCl + HSO 4 15.1.4 Acid-base reactions When an acid and a base react, they neutralise each other to form a salt . If the base contains hydroxide (OH ) ions, then water will also be formed. The word salt is a general term which applies to the products of all acid-base reactions. A salt is a product that is made up of the cation from a base and the anion from an acid. When an acid reacts with a base, they neutralise each other. In other words, the acid becomes less acidic and the base becomes less basic. Look at the following examples: 1. Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (the salt) and water. Sodium chloride is made up of Na + cations from the base (NaOH) and Cl anions from the acid (HCl). HCl + NaOH H 2 O + NaCl 2. Hydrogen bromide reacts with potassium hydroxide to form potassium bromide (the salt) and water. Potassium bromide is made up of K + cations from the base (KOH) and Br anions from the acid (HBr). HBr + KOH H 2 O + KBr 270
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CHAPTER 15. TYPES OF REACTIONS - GRADE 11 15.1 3. Hydrochloric acid reacts with sodium hydrocarbonate to form sodium chloride (the salt) and hydrogen carbonate. Sodium chloride is made up of Na + cations from the base (NaHCO 3 ) and Cl anions from the acid (HCl). HCl + NaHCO 3 H 2 CO 3 + NaCl You should notice that in the first two examples, the base contained OH ions, and therefore the products were a salt and water . NaCl (table salt) and KBr are both salts. In the third example, NaHCO 3 also acts as a base, despite not having OH ions. A salt is still formed as one of the products, but no water is produced. It is important to realise how important these neutralisation reactions are. Below are some examples: Domestic uses Calcium oxide (CaO) is put on soil that is too acid. Powdered limestone (CaCO 3 ) can also be used but its action is much slower and less effective. These substances can also be used on a larger scale in farming and also in rivers. Biological uses Acids in the stomach (e.g. hydrochloric acid) play an important role in helping to digest food. However, when a person has a stomach ulcer, or when there is too much acid in the stomach, these acids can cause a lot of pain. Antacids are taken to neutralise the acids so that they don’t burn as much. Antacids are bases which neutralise the acid. Examples of antacids are aluminium hydroxide, magnesium hydroxide (’milk of magnesia’) and sodium bicarbonate (’bicarbonate of soda’). Antacids can also be used to relieve heartburn.
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