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

2. 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

3. 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

4. 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

5. 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.

6. 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

7. 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
strong
acid
weak acid
neutral

8. 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

9. 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
neutral
weak base
strong base

10. 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

11. 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

12. 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)