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Introducing Acids and Bases

Introducing Acids and Bases. Chapter 13. Acids. 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.

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Introducing Acids and Bases

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  1. Introducing Acids and Bases Chapter 13

  2. Acids • 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. • Vinegars have ethanoic acid, orange juice contains citric acid and soft drinks contain carbonic acid.

  3. Acids • Acids in foods are not strong. • Can anyone tell me three common laboratory acids. • 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.

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

  5. Bases • React with 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.

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

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

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

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

  10. Indicators

  11. 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. • It does not mean NaCl. • 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. • The salt produced will depend on the acid used.

  12. Reaction Type 1 • Acid + reactive metal ―› salt + hydrogen • Reactive metals include Ca, Mg, K and Zn but not Cu, Ag or Au • For example 2HCl(aq) + Zn(s) ―› ZnCl2(aq) + H2 (g) Who can write this equation as an ionic equation??

  13. Reaction Type 2 • Acid + metal hydroxide ―› salt + water • Metal hydroxides include NaOH, Ca(OH)2 and Mg(OH)2. For example H2SO4(aq) + 2NaOH(aq) ―› Na2SO4(aq) + 2H2O(l) Write the ionic equation and write the spectator ions down.

  14. Reaction Type 3 • Acid + metal oxide ―› salt + water • Metal oxides include Na2O, MgO, CaO and ZnO Give me an example of an equation if nitric acid reacts with solid calcium oxide.

  15. Reaction Type 4 • Acid + metal carbonate ―› salt + water + carbon dioxide • Metal carbonates include Na2CO3, MgCO3 and CaCO3 Show an equation for nitric acid reacting with MgCO3. Show both the balanced equation and the ionic equation.

  16. Reaction Type 5 • Acid + metal hydrogen carbonate ―› salt + water + carbon dioxide • Metal hydrogen carbonates include NaHCO3, KHCO3 and Ca(HCO3)2. HCl(aq) + NaHCO3(aq) ―› NaCl(aq) + H2O(l) + CO2(g) Ionic Equation H+(aq) + HCO3-(aq) ―› H2O(l) + CO2(g)

  17. Reaction Type 6 • Acidic oxide (non-metal oxide) + base ―› salt + water • Acidic oxides include SO2, SO3, P4O10 and CO2. CO2(aq) + Ca(OH)2(aq) ―› CaCO2(aq) + H2O(l)

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