Explain pH and how neutralisation occurs Learning Objective To be able to: Explain pH and how neutralisation occurs Key Words: Ions, water, pH

Exam question Friday, 24 May 2019 pH and Neutralisation Date and title in books. You need a pen, pencil & ruler. Starter Activity – 5 minutes Exam question

Learning Outcomes Identify the ions in an acid and an alkali Target 9-1 Identify the ions in an acid and an alkali (F/H) Target 4-9 Describe how neutralisation occurs (H) Target 5-9 Explain, using ions, how water is produced during neutralisation reactions Extension: Application of Knowledge Target 8/9 Write balanced equations for a range of reactions Learning Outcomes

What are acids and alkalis? Boardworks GCSE Additional Science: Chemistry Acids and Alkalis Photo credits: vinegar © Ivaylo Ivanov, Shutterstock.com 2011; fertillizer © flashgun, Shutterstock.com 2011

Boardworks GCSE Additional Science: Chemistry What are bases? Boardworks GCSE Additional Science: Chemistry Acids and Alkalis All alkalis are bases. Bases are substances that react with acids by absorbing hydrogen ions (H+). The oxides, hydroxides and carbonates of metals, such as sodium hydroxide, are bases. Some bases are soluble in water. These are called alkalis. All alkalis contain hydroxide ions (OH–). The more OH– ions in the solution, the stronger the alkali.

What does the pH scale show? Boardworks GCSE Additional Science: Chemistry Acids and Alkalis The pH scale runs from 1 to 14. The numbers 1 to 6 represent acidic conditions and 8 to 14 represent alkali conditions. A pH value 7 is neutral. What are the pH values of some everyday items? 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acids strong weak acid acid neutral What are acids? They are substances that: Have a pH below 7. Turn litmus red. Turn universal indicator yellow, orange or red. Form solutions containing H+ ions. The more H+ ions in the solution, the stronger the acid. Universal indicator pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 strong acid weak acid neutral

Common acids What are some common acids? Acid Formula Strength sulfuric acid H2SO4 strong hydrochloric acid HCl strong nitric acid HNO3 strong ethanoic acid (vinegar) CH3COOH weak 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Bases weak base strong base neutral What are bases? They are substances that: Have a pH above 7. Turn litmus blue. Turn universal indicator dark green, blue or purple. Are capable of neutralizing acids. Universal indicator pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 neutral weak base strong base

Common bases What are some common bases? Base Formula Strength sodium hydroxide * NaOH strong potassium hydroxide * KOH strong calcium hydroxide * Ca(OH)2 strong ammonia * NH3 weak calcium carbonate CaCO3 weak * = the base is also an alkali 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neutralization reactions A neutralization reaction occurs when an acid reacts with a base or alkali to produce a neutral solution of salt and water. alkali salt acid  + water

H+ (aq) + OH- (aq)  H2O (l) Producing Water In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation: H+ (aq) + OH- (aq)  H2O (l)