Introducing Acids and Bases Chapter 13

Acids Acids are commonly used in our homes. Acids are commonly used in our homes. They are used in many foods to enhance the flavour, the sour tastes in many foods is due to their acid content. They are used in many foods to enhance the flavour, the sour tastes in many foods is due to their acid content. Vinegars have ethanoic acid, orange juice contains citric acid and soft drinks contain carbonic acid. Vinegars have ethanoic acid, orange juice contains citric acid and soft drinks contain carbonic acid.

Acids Acids in foods are not strong. Acids in foods are not strong. Can anyone tell me three common laboratory acids. Can anyone tell me three common laboratory acids. Acids can be dangerous when misused. They can cause severe burns due to corrosion. Acids can be dangerous when misused. They can cause severe burns due to corrosion. Acid rain causes soils to become ‘sour’ and stunts plant growth. Acid rain causes soils to become ‘sour’ and stunts plant growth.

Properties of Acids In general, acids can: In general, acids can: Change the colour of some indicators Change the colour of some indicators Be corrosive Be corrosive Taste sour Taste sour React with bases React with bases Have a relatively low pH Have a relatively low pH

Bases React with acids. React with acids. Can be just as dangerous as acids. Can be just as dangerous as acids. Bases are effective cleaners because they can react with fats or oils to produce water soluble soaps. Bases are effective cleaners because they can react with fats or oils to produce water soluble soaps.

Bases In general bases can: In general bases can: Turn litmus paper blue Turn litmus paper blue Have a slippery feel Have a slippery feel Are caustic Are caustic React with acids React with acids Have a relatively high pH Have a relatively high pH

Neutralisation When an acid and base react to form a solution of salt and water. When an acid and base react to form a solution of salt and water. This is called neutralisation. This is called neutralisation. Acids and bases are said to neutralise each other. Acids and bases are said to neutralise each other. That is the eliminate each others properties. That is the eliminate each others properties. Some neutralisation reactions are very dangerous however. Some neutralisation reactions are very dangerous however.

Safety Wear safety glasses Wear safety glasses Wear a lab coat Wear a lab coat Label bottles and containers. Label bottles and containers. If possible store separately If possible store separately When diluting acids, add the acid to the water and not the water to the acid. When diluting acids, add the acid to the water and not the water to the acid. Why might we use these precautions? Why might we use these precautions?

Indicators A substance that has different colours depending on its acid or base form. A substance that has different colours depending on its acid or base form. Litmus paper is red for acids and blue for bases. Litmus paper is red for acids and blue for bases. Indicators themselves can be acids or bases. Indicators themselves can be acids or bases. They change from one colour in acid to another one in basic solutions They change from one colour in acid to another one in basic solutions

Indicators

Reactions involving acids and bases Before we begin you need to note that when we say a salt. It does not mean table salt that you put on your chips. Before we begin you need to note that when we say a salt. It does not mean table salt that you put on your chips. It does not mean NaCl. It does not mean NaCl. A salt can be a compound that is derived from an acid. A salt can be a compound that is derived from an acid. Salts are usually made up of a metal cation and a non-metal anion. Salts are usually made up of a metal cation and a non-metal anion. The salt produced will depend on the acid used. The salt produced will depend on the acid used.

Reaction Type 1 Acid + reactive metal ―› salt + hydrogen Acid + reactive metal ―› salt + hydrogen Reactive metals include Ca, Mg, K and Zn but not Cu, Ag or Au Reactive metals include Ca, Mg, K and Zn but not Cu, Ag or Au For example For example 2HCl(aq) + Zn(s) ―› ZnCl 2 (aq) + H 2 (g) Who can write this equation as an ionic equation??

Reaction Type 2 Acid + metal hydroxide ―› salt + water Acid + metal hydroxide ―› salt + water Metal hydroxides include NaOH, Ca(OH) 2 and Mg(OH) 2. Metal hydroxides include NaOH, Ca(OH) 2 and Mg(OH) 2. For example H 2 SO 4 (aq) + 2NaOH(aq) ―› Na 2 SO 4 (aq) + 2H 2 O(l) Write the ionic equation and write the spectator ions down.

Reaction Type 3 Acid + metal oxide ―› salt + water Acid + metal oxide ―› salt + water Metal oxides include Na 2 O, MgO, CaO and ZnO Metal oxides include Na 2 O, MgO, CaO and ZnO Give me an example of an equation if nitric acid reacts with solid calcium oxide.

Reaction Type 4 Acid + metal carbonate ―› salt + water + carbon dioxide Acid + metal carbonate ―› salt + water + carbon dioxide Metal carbonates include Na 2 CO 3, MgCO 3 and CaCO 3 Metal carbonates include Na 2 CO 3, MgCO 3 and CaCO 3 Show an equation for nitric acid reacting with MgCO 3. Show both the balanced equation and the ionic equation.

Reaction Type 5 Acid + metal hydrogen carbonate ―› Acid + metal hydrogen carbonate ―› salt + water + carbon dioxide salt + water + carbon dioxide Metal hydrogen carbonates include NaHCO 3, KHCO 3 and Ca(HCO 3 ) 2. Metal hydrogen carbonates include NaHCO 3, KHCO 3 and Ca(HCO 3 ) 2. HCl(aq) + NaHCO 3 (aq) ―› NaCl(aq) + H 2 O(l) + CO 2 (g) Ionic Equation H + (aq) + HCO 3 - (aq) ―› H 2 O(l) + CO 2 (g)

Reaction Type 6 Acidic oxide (non-metal oxide) + base ―› salt + water Acidic oxide (non-metal oxide) + base ―› salt + water Acidic oxides include SO 2, SO 3, P 4 O 10 and CO 2. Acidic oxides include SO 2, SO 3, P 4 O 10 and CO 2. CO 2 (aq) + Ca(OH) 2 (aq) ―› CaCO 2 (aq) + H 2 O(l)