Thinking about salt hydrolysis

Salt hydrolysis is difficult. To help my students grapple with this concept I used a routine from the visible thinking

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project called the 4C’s.

  1. Connect
  2. Challenge
  3. Concept
  4. Change

In this activity the thinking centres on a text that explains salt hydrolysis. This could be a relevant chapter in the textbook, a webpage that explains salt hydrolysis or a teacher produced document. The students use the text to make connections between salt hydrolysis and prior knowledge, ask questions, identify key ideas and consider applications.

This routine works best when the text incorporates complex ideas, concepts or perspectives that students grapple with. It is this grappling that promotes deep thinking and meaningful discussion. In this regard, the text is far more than a source of information but provides a context for focusing the discussion on what matters and for developing thinking skills.

Steps

1. The 4C’s are described and the students told that they will form the framework for the discussion.

2. Students read the text independently and identify a connection, challenge, concept, change.

  • What connections can you make to what you already know or have learned? In other words what can you identify with?
  • What challenges do you face in learning about salt hydrolysis? Is there anything else you need to know before you move on?
  • What are key concepts / understandings? These are important ideas that you might share with someone who asks about the salts formed in neutralization reactions.
  • What are the implications of knowing this? Why is knowing this important? How did it change the way you think? Be prepared to give reasons and justification.

3. Students share their 4C’s, starting first with a round of connections, followed by rounds of challenges, concepts and changes.

The student’s 4C’s gave me insights into their understanding of salt hydrolysis and how it fitted conceptually within the wider context of acid-base chemistry. The challenges they shared provided good data for me to assess where they were in their learning, enabling me to direct further teaching.

Some of the student challenges!

Understanding why when the charge on the metal ion increased, and the ionic radius decreases that their is a greater tendency for a salt to react with water.

I don’t know how to predict the pH of a salt

In the case where both acid/base conjugates are strong how is the kind of salt determined.

There are many reactions taking place and I am not sure of the significance is of each.

When and where do we use Bronsted-Lowry and Lewis theories.

It is worth noting that each of the C’s can stand alone. For example, at the end of a discussion / lesson students could be asked what connection they made with the lesson today and other work.

IB Links NOTES
Prior knowledge Theories and properties of acids and bases. pH scale Strong and weak acids and bases. pH curves
Chemistry syllabus & cross curricular links (first exams 2016) 18.3
Learner Profile attributes Thinkers, Knowledgeable, Reflective
Approaches to Learning Thinking skills

Reference:

Ritchhart, R., Church, M., & Morrison. (2011). Making Thinking Visible. San Francisco: Josseyboss.

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