Teaching school science within the cognitive and affective domains

Chemical Reaction

After viewing the experiment on the video clips, which experiment produces a more violent reaction when the metal was thrown into the beaker of water?

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Potassium reacts with water vigorously/explosively but iron reacts very slowly with water.

These examples can be likened to situations when others throw abusive comments or tease us in order to lure us into a fight or quarrel. We can impulsively fight back or we can remain calm and not be drawn into a fight.

a. Which metal - potassium or iron, do you think best describes your emotional reaction when you are being verbally abused or teased?

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b. After potassium has reacted, the reaction mixture is hot and becomes a very strong (caustic) alkali because potassium hydroxide is produced.

If your emotional reaction is like the way potassium reacts, describe briefly what may happen to you or your loved ones after you have been involved in a fight or an uncontrolled quarrel with someone else.

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The reactivities of sodium and potassium metals can be controlled by putting them in oil which separates them from air.

Think of a situation in which some people you know had a heated argument. How did you, borrowing the idea of sodium/potassium in oil, stop their quarrelling?

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MESSAGE: We should control our emotions, especially in the event that others are challenging us to a quarrel/fight. It is always good to have someone (acting like oil) to separate us from them, thus preventing a possible fight that may result in injuries.

Sample student responses:

B Lesson 2: Activity on separation techniques (Sec 3 Express)

Sedimentation

You are provided with two mixtures:

Observe Mixture (A) and write your observation in the table provided below.

Now shake Mixture (B) gently by swirling the container until a suspension is formed.

Observe Mixture (B) after you have shaken the container and placed it on your bench. Then write your observation in the table provided below.

Compare your observations on these 2 mixtures below:

Mixture A (left standing untouched overnight)

Mixture B (which you have just shaken/stirred)

Why is Mixture (B), when shaken, often referred to as a suspension but not Mixture (A)?

By allowing the mixture to settle, sand can be separated from the water. Suggest another method by which sand can be separated from water.

Reflection

If you have a quarrel with your best friends, which of the two mixtures [Mixture (A) or Mixture (B)] would represent your emotion (or confusion)?

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You would have observed that by allowing the shaken Mixture (B) to stand untouched for some time it will soon appear to look like Mixture (A).

Using this observation, suggest how would you attempt to deal with your emotions (or confusion) in the situation where you had been quarrelling with your friends.

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Sample student responses:

(1) If you have a quarrel with your best friends, which of the 2 mixtures [(A) or (B)] would represent your emotion (or confusion)?

All responded to question (1) with “Mixture B”.

(2) You would have observed that by allowing the shaken Mixture (B) to stand untouched for sometime it will soon appear to look like Mixture (A). Suggest how you would attempt to separate your emotion (or confusion) in the situation when you have been quarrelling with your friends.

“I would leave myself alone to cool down and soon my mood will stop changing easily. Things will become easier to see too.”

C Lesson 3: Reactions of weak and strong acids (Sec 2 Express)

Aim: To compare the reaction characteristics of weak and strong acids.

Apparatus & materials: Hydrochloric acid, ethanoic acid, magnesium ribbon, test tubes.

Procedure:

(a) Pour 3 cm3 of aqueous hydrochloric acid into test tube A.
(b) Pour 3 cm3 of aqueous ethanoic acid into test tube B.

Put in a piece of magnesium ribbon into test tube A, then observe.
(a) Record your observations.
(b) Insert a burning splint into the mouth of the test tube. A ‘pop’ sound indicates that the gas produced is hydrogen.
(c) Repeat steps 1 and 2 for test tube B.

Observations:

Describe what happen when the magnesium ribbon is added to hydrochloric acid.

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Describe what happens when burning splint is introduced.

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Which solution is a weak acid? Hydrochloric acid or ethanoic acid?

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Is the action of weak acid more vigorous or less vigorous than the action of strong acid?

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Conclusion: Complete the following word equation
Therefore, Acid + ___________________ à Salt + ____________________

The following are some expected observations from the experiment with hydrochloric acid, a strong acid and ethanoic acid, a weak acid (the same volume being reacted with a fixed length of magnesium ribbon).

Observation within same time frame (say 5 minutes)	Strong acid	Weak acid
Rate of bubbles produced (visual inspection)	fast	slow
Amount of gas evolved	more	less
Amount of solid reactant used up	more	less

If the magnesium ribbon represents your monthly allowance (say S$300/-) would you consider your spending habits to be similar to the reaction characteristics of the strong acid or the weak acid?

Explain your daily life experiences based on your answer in (1).

Do you think this is an important value to embrace, or habit to practice in life? Why?

Do you think your habit will help you in times of emergency?

Sample student responses:

¹ Student response has been edited by first author for the purpose of replacing student’s original word with a similar and more appropriate phrase.