1. © OUP: To be used solely in purchaser’s school or college 7E Acids and alkalis Acids and alkalis Indicators Neutralisation 7E Acids and alkalis

2. © OUP: To be used solely in purchaser’s school or college 7E Acids and alkalis Acids and alkalis

3. © OUP: To be used solely in purchaser’s school or college 7E Acids and alkalis - Where are they found?

4. © OUP: To be used solely in purchaser’s school or college 7E Acids and alkalis - Concentrated and dilute Compare the particle model of a concentrated acid with a weak acid. Which sentence best describes which acid? A. This acid has only a few acid particles compared to water particles. B. This acid has a lot of acid particles compared to water particles. Why is a dilute acid less hazardous than a concentrated acid? concentrated acidweak acid

5. © OUP: To be used solely in purchaser’s school or college FALSE! The Latin word “acere” means “sour”. Acids have a sour or bitter taste. 7E Acids and alkalis - True or false? True or False? FALSE! Ethanoic acid is the chemical name for vinegar. Vinegar on pancakes - YUCK! Most people prefer citric acid in lemon juice. TRUE! Pure water is called neutral. In nature, rainwater is weakly acidic and seawater is weakly alkaline. FALSE! They are called corrosive. Dangerous alkalis are sometimes called caustic. FALSE! Only strong acids are dangerous. Weaker acids, like citric acid, are not harmful to skin. TRUE! Arabic chemists used to make alkalis from the remains of plant ashes. 1. The word acid comes from the Latin word “acere” meaning “sweet”. 2. The word “alkali” comes from the Arabic “al-qily” which means “plant ashes”. 3. All acids are dangerous and can burn skin.4. Acids and alkalis that are dangerous to taste and touch are called caustic. 5. Pure water is not an acid or an alkali.6. The acid some people like to put on pancakes is called ethanoic acid.

6. © OUP: To be used solely in purchaser’s school or college 7E Acids and alkalis Indicators

7. © OUP: To be used solely in purchaser’s school or college Litmus is always red in an acid. 7E Indicators - What is an indicator? How can you tell if a solution is an acid or an alkali? Some chemicals have different colours in acid or alkaline solutions. These coloured chemicals are called indicators. Litmus indicator is a vegetable dye. Litmus is purple in water.Litmus is always blue in an alkali.

8. © OUP: To be used solely in purchaser’s school or college 7E Indicators – Litmus test

9. © OUP: To be used solely in purchaser’s school or college 7E Indicators – Universal and pH scale universal indicator pH scale pH FACT: The pH scale was invented in 1909 by Soren Sorenson, a Danish chemist who was working on beer quality! To tell the strength of an acid or alkali we need an accurate indicator called … It shows the strength of acids and alkalis based on the… How can you tell if an acid or alkali is weak or strong? Universal indicator is a mixture of several indicators.

10. © OUP: To be used solely in purchaser’s school or college

11. 7E Acids and alkalis Neutralisation

12. © OUP: To be used solely in purchaser’s school or college 7E Neutralisation - What is neutralisation? What happens to pH when an alkali is added to an acid? An acid has a pH less than 7. acid + universal indicator An alkali has a pH greater than 7. alkali + universal indicator

13. © OUP: To be used solely in purchaser’s school or college Why has the indicator turned green? Mix an acid and an alkali together and a chemical reaction takes place. 7E Neutralisation - What is neutralisation?

14. © OUP: To be used solely in purchaser’s school or college What would happen to the pH value if more acid was added to the mixture? If the right amounts of an acid and an alkali are added together the pH of the mixture changes to neutral (pH 7). This reaction is neutralisation. 7E Neutralisation - What is neutralisation? What would happen to the pH value if more alkali was added to the mixture? acid + alkali neutral solution

15. © OUP: To be used solely in purchaser’s school or college 7E Neutralisation - Using neutralisation Neutralisation can be a very useful reaction. Match each problem with the correct neutralising treatment. 5. Mouth bacteria produce acid from sugary foods 4. Nettle sting contains acid which irritates skin 3. Power stations produce gas which forms acid rain 2. Acid rain pollutes lakes and poisons wildlife 1. Indigestion caused by too much stomach acid Acidic problem E. Calcium carbonate reduces acidity of water D. Calcium carbonate neutralises acidic gas before it is released C. Antacid tablets B. Regular brushing with alkaline toothpaste A. Rub with leaves of alkaline plant Neutralising treatment