QCY520 Problem Solving - Students

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teacher education ▪ research ▪ outreach

QCY520

The Teaching of

Chemistry I

Problem Solving Oct

2013

Ms Low Bee Yen

[email protected]

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Teaching Problem Solving Skills Classification of Problems

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Introduction

N₂ + 3 H₂ → 2 NH₃

What is left in the reaction flask when 4 moles of nitrogen and 6 moles of hydrogen are

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Introduction

Students have difficulty solving problems in chemistry, such as

• Stoichiometry

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Introduction

Main reasons for difficulty

• Cannot understand the problem statement • Cannot link the problem statement to their

knowledge/cannot apply their knowledge to the problem

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Classification of Problems

(Johnstone, 1993)

Type Data Methods Goals/

outcome Skills bonus

1 Given Familiar Given Recall of algorithms

2 Given Unfamiliar Given Looking for parallels to known methods

3 Incomplete Familiar Given Analysis of problem to decide what further data are required

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Classification of Problems

Chain of reasoning involved such as: “If I knew the mass of the coin and if I assumed that it was pure copper and if I had the atomic mass of copper and Avogadro’s number, I could get an answer, but it would only be approximate. But if I have no balance and only a ruler, I could get its volume (approximately) and if I knew the density of copper, I could get a good estimate”.

(Wood, 2006)

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Classification of Problems

(Johnstone, 1993)

5 Given Familiar Open

Decision making about appropriate goals. Exploration of knowledge networks

6 Given Unfamiliar Open

Decisions about goals and choices of appropriate methods. Exploration of knowledge

and technique networks

7 Incomplete Familiar Open

Once goals have been specified by the student, these data are seen to be incomplete

8 Incomplete Unfamiliar Open

Suggestion of goals and methods to get there; consequent need for

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Classification of Problems

This could yield a range of responses, including the oxidation state of the cobalt ion and its ‘d’-electron

configuration, the name of the complex, its percentage composition, its isomers, its likely reactions, and so on.

(Wood, 2006)

Type 5 – much more open and is left to the judgments of the student as to what would constitute a reasonable

answer.

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Classification of Problems

(Johnstone, 1993)

5 Given Familiar Open

Decision making about appropriate goals. Exploration of knowledge networks

6 Given Unfamiliar Open

Decisions about goals and choices of appropriate methods. Exploration of knowledge

and technique networks

7 Incomplete Familiar Open

Once goals have been specified by the student, these data are seen to be incomplete

8 Incomplete Unfamiliar Open

Suggestion of goals and methods to get there; consequent need for

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• Translate the Problem

• Search for solution

• Evaluate the solution

Steps to Solve a Problem

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Translate the Problem

Understand the whole problem statement

• what type of problem? (rate of reaction, etc)

• what is to be solved?

• what do you have to know to solve the problem?

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Translate the Problem

N₂ + 3 H₂ → 2 NH₃

What is left in the reaction flask when 4 moles of nitrogen and 6 moles of hydrogen are

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Translate the Problem

Magnesium oxide has the same geometric form of crystal lattice as sodium chloride. Draw a

diagram showing the arrangement and type of

particles present in a crystal of magnesium oxide.

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Translate the Problem

Magnesium oxide has the same geometric form of crystal lattice as sodium chloride. Draw a

diagram showing the arrangement and type of

particles present in a crystal of magnesium oxide.

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Translate the Problem

• What is magnesium oxide? • What is a crystal lattice?

• What is sodium chloride?

• What is the crystal lattice of sodium chloride • Draw crystal structure (not dot-and-cross

diagram!) of sodium chloride.

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Search for Solution

• Select information from translation

• Retrieve information from memory

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Search for Solution

• Magnesium is a metal, oxygen is a non-metal

• Compound formed is MgO and ionic.

• A crystal lattice shows the arrangement of particles in a solid

• There are Mg2+ and O2- ions in the crystal lattice.

• Sodium is a metal, chlorine is a non-metal

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Search for Solution

• In the crystal lattice of sodium chloride, each sodium ion has 6 neighbouring chloride ions and vice versa.

• MgO has similar structure as NaCl.

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Exercises

When 5.40g of an oxide of uranium 238 (U) were reduced, 4.76g of uranium metal were obtained. Calculate the

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Exercises

Electrolysis of a concentrated aqueous solution of potassium chloride using carbon electrodes gave a

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Exercises

P, a pure solid, is a good conductor of electricity. P reacts with dilute HCl forming a green solution, Q. Chlorine

reacts with solution Q forming a yellow solution R. Identify

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Exercises

T is a pure, white solid which dissolves in water. When NaOH is added to a solution of T, a white ppt, U, is

formed which dissolves in excess NaOH. When silver

nitrate (aq) is added to a solution of T in dilute nitric acid, a white ppt, V, is formed. Identify V. Draw as many

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Cognitive Requirements

Students need problem translation skills – accuracy, especially for unfamiliar problems.

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Cognitive Requirements

Many students do not understand the chemistry concepts involved in the problem or cannot apply their knowledge to solve the problem.

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Teaching Linking Skills

Word association • combustion • metal

Idea association (big picture) • ethanol

• chromatography

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In an electrolysis experiment, the same

current deposited 16 g of copper and 6 g of titanium for a given time.

What was the charge on the titanium ion?

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Outline how you would prepare lead(II) sulfate from lead(II) oxide.

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Teaching Translation Skills

Understand the whole problem statement (overview)

• What type of problem? • What is to be solved?

• Use of diagrams and symbols.

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Teaching Translation Skills

Translating parts of problem statement / setting goals or subgoals (specific)

• Underline important key words.

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Teaching Translation Skills

Whimbey’s Think-Aloud Pair method

Listener to encourage problem solver to • verbalise every stage

Elaborate

• Do not let the problem solver continue if you do not understand what he/she has done. • You think a mistake has been made

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Teaching Translation Skills

Whimbey’s Think-Aloud Pair method

• Metacognition – awareness of what one is doing during problem solving.

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Teaching Translation Skills

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Teaching Translation Skills

Selenium (Se) is in Group VI and has a relative atomic mass of 79. The chemistry of selenium closely resembles that of sulfur. Selenium burns in oxygen to form an oxide which contains 71.2% by mass of selenium. When this oxide is heated with an excess of magnesium, a mixture of

magnesium oxide and magnesium selenide is

formed. Addition of dilute hydrochloric acid to this mixture results in the formation of a colourless

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Summary

Problem solving

Translate the problem

• making sense of problems and linking

problem with prior knowledge

Search for solution

• previous problems encountered and

algorithms used

Evaluate solution

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References

• Tan, A-G., Lee, K-W.L., Goh, N-K., & Chia, L-S. (Eds.) (2002). New paradigms for science education. Singapore: Prentice Hall. Part I, pp. 15-75.

• Gabel, D.L. & Bunce, D.M. (1994). Research on problem solving: chemistry. In D.L. Gabel (Ed.), Handbook of research on science teaching and learning (pp. 177-210). New York: Macmillan.

• Reid, N., & Yang, M.-J. (2002). The solving of problems in

chemistry: the more open-ended problems. Research in Science and Technological Education, 20(1), 83-98.