Equilibria · SHS3 Chemistry

Lesson notes

Learning Objectives

Indicator: 3.1.2.LI.1 - Explain acid-base indicator, determine a suitable indicator for a titration and draw graphs to represent titration.

By the end of the lesson, learners can:

Define an acid-base indicator and explain its nature as a weak acid or weak base whose colour changes over a specific pH range.
State the working pH range of common indicators including litmus, phenolphthalein, methyl orange, and methyl red.
Explain why the choice of indicator for a titration depends on the nature of the acid and base used, the type of salt formed, and the steep part of the titration curve.
Sketch and label titration curves for all four combinations of strong and weak acids titrated against strong and weak bases.
Select and justify the most suitable indicator for a given acid-base titration by referring to the pH range of the indicator and the vertical portion (equivalence point region) of the titration curve.

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Curriculum details

Strand: Physical Chemistry (Strand 1)
Sub-strand: Equilibria (1.2)
Content standard: 3.1.2.CS.3 - Demonstrate understanding of concepts of hydrolysis of salt in the choice of indicators based on titration curves. 3.1.2.LO.1 Use the knowledge in pH to distinguish between solutions that are acidic, neutral or basic. 5 Gender Equality and Social Inclusion 6 Socio-Emotional Learning 3.1.2.LO.2 Use your knowledge and understanding of concepts in hydration and hydrolysis to determine the types of salts. 3.1.2.LO.3 Use the understanding of hydrolysis of salts to decide on suitable indicator as well as plot and interpret titration curves. 3.1.2.LO.4 Describe oxidation and reduction reactions and apply their principles to electrochemical cells as well as their importance in everyday life.
Indicator: 3.1.2.LI.1 - Explain acid-base indicator, determine a suitable indicator for a titration and draw graphs to represent titration.
Suggested placement: Semester 1, Week 11 (Week 11 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: NaCCA curriculum document, p. 98

Exemplars (from the NaCCA curriculum)

Collaborative Learning:
- In mixed gender-based groups, discuss acid-base indicators, their nature and their respective working ranges.
- Discuss the suitable indicator for an acid-base titration reaction taking into consideration the nature of the acid and base involved, the type of salt formed and the working range of acid-base indicators.
Exploratory Learning: Work in groups to explore the use of different indicators for undertaking titrations in the laboratory.
Activity-Based Learning: Draw or sketch an acid-base titration curve and indicate the appropriate indicator for: a. Strong acid against a strong base b. Strong acid against a weak base c. Weak acid against a strong base d. Weak acid against a weak base
Teaching and Learning Materials:
- * Acid-base indicators * Acidic substance
- * Basic substance * Beaker
- * Graph
- board
Assessment (3.1.2.AS.1). The document marks these depth-of-knowledge levels for this indicator: Level 3 Strategic reasoning.