Acids and Alkalis(bases)

1. Acids and Alkalis(bases) Learning Objectives • To know that solutions can be sorted by whether they are: acid, alkali or neutral. • To understand that an alkali reacts with an acid to cancel it out. • To know that indicators show you how acidic or alkaline a solution is.

4. Acids and alkalis Show video on acids and alkalis Answer the following questions from the video. • What does the warning symbol on acids mean? • What are the common acids? • What is an alkali? • Can metals be dissolved by acids and alkalis, give and example. • What is an indicator. • What is the pH of neutral substance? • How can you measure the pH of shampoo? • What is litmus paper? What colour is it in acid/base?

5. Acids and alkalis When a substance dissolves in water it makes a solution. Solutions can be sorted by whether they are: acid, alkali or neutral.

6. Acids and Bases • Acids and bases are substances with certain physical and chemical properties • We can determine if substances are acidic or basic by testing their pH or by indicators.

7. Acids have a sour taste. They are corrosive. They have pH of <7 The acid in car batteries is sulfuric acid.

8. Acids There are many acids present in our everyday lives. Lemon juicecontainscitric acid,andvinegar contains ethanoic acid. Some strong acids are hydrochloric acid, sulphuric acid and nitric acid. Some weak acids are ethanoic acid, citric acid and carbonic acid.

9. Common bases (alkalis) Drain Cleaners Soap Stomach upset cures.

10. Alkalis (Bases) Many everyday substances are alkalis. They feel soapy. They are corrosive. Bases (alkalis) have ph > 7 Alkalis react with acids and neutralisethem.

11. Alkalis (base that dissolve in water) Alkalis are present in many cleaning substances in use in our homes. Kitchen cleaners are alkaline because they contain ammonia or sodium hydroxide, which attack grease. Calcium hydroxide and sodium hydroxide arestrong alkalis. The most recognisable and common weak alkali is ammonia.

12. Indicators • Organic substances that change color in the presence of an acid or a base. • Red cabbage juice will change color in the presence of acids or bases

13. Indicators Indicators help you find out whether a solution is acidic or not. They change colour in acid or alkaline solutions. Different indicators change to different colours.

14. LitmusTest • Litmus is an indicator. It changes colour in acid and alkaline solutions. • Litmus is red in an acid. • Litmus is blue in an alkali.

15. Universal Indicator • Universal indicator changes colour in acids and alkalis. ACIDS ALKALIS Neutral Its colour shows the strength of an acid or alkali.

16. The pH scale 1 – 6 8 - 14 Alkalis 7 Acids Neutral

17. Measuring pH • pH can be measured using a ph meter. Simply put the sensor in a solution and read the pH. • pH can measured using universal indicator, comparing the colour on chart for pH

18. Common Laboratory Acids The two most common laboratory acids are • sulfuric acid (H2SO4) • Hydrochloric acid (HCl)

19. Bases • Named just like other ionic compounds • Name these bases: • Ca(OH)2 • NaOH • NH4OH calcium hydroxide sodium hydroxide ammonium hydroxide

20. Neutralisation • Acids and alkalis react with each other. The alkali cancels out the acid in the reaction. This is called neutralisation. Acid + Base = Water + Salt Hydrochloric + Sodium  Sodium + Water Acid hydroxide Chloride (PASS) Ex: HCl+ NaOH  H2O + NaCl (Honours) A saltis made. A neutral substance no longer acts as an acid or a base

21. Applications of Neutralisation • Insect Stings Bee stings are acidic and can be neutralised with baking soda (bicarbonate of soda). Wasp stings are alkaline and can be neutralised with vinegar. • Indigestion: Our stomach carries around hydrochloric acid. Too much of this leads to indigestion. To cure indigestion, you can neutralise the excess acid with baking soda or specialised indigestion tablets.

22. Soil Treatment: When soils are too acidic (often as a result of acid rain) they can be treated with slaked lime, chalk or quicklime, all alkalis. Plants and crops grow best in neutral soils. More Applications of Neutralisation Factory Waste: Liquid waste from factories is often acidic. If it reaches a river it will destroy and kill sea life of many forms. Neutralising the waste with slaked lime can prevent this.

23. Acids react with bases and carbonates. Acid + Base Salt + Water sulfuric acid + sodium sulfate + sodium hydroxide water Acid + Carbonate Salt + Water + Carbon dioxide sulphuric acid + copper sulphate + water + copper carbonate carbon dioxide

24. Salts • A salt is formed when the hydrogen in an acid is replaced by a metal • The salt made depends on the acid and base used. • The salt contains the metal atom from the alkali, and part of the acid molecule. The salts of sulphuric acid are known as sulfates. The salts of hydrochloric acid are known as chlorides. The salts of nitric acid are known as nitrates.

25. Making a Salt by Titration Hydrochloric Acid (HCl) • Titration is way of adding an acid (in a burette) (HCl) slowly to a base (in conical flask) (NaOH) until the acid is neutralised. • Acid is added dropwise until the indicator (methyl orange) just changes colour (yellow to pink). • The liquid in the conical flask is then evaporated to get the salt. (NaCl) Burette Conical flask Sodium Hydroxide (NaOH)