Representing chemical reactions | Structure strip

Structure strips can be used to support and promote independent writing. Learners will write about chemical reactions using key terms, compare word and symbol equations and write independently about balanced symbol equations. 

Learning objectives

1. Recall the definition of reactants and products.
2. Compare and contrast the features of word and symbol equations.
3. Interpret chemical formulas to balance symbol equations.

Introduction

Chemical reactions can be represented using word equations or balanced symbol equations. Word equations show the names of the reactants and the products separated by an arrow. Balanced symbol equations give more detail, showing the reactants and products, how they are bonded together and how mass is conserved by balancing the equation. Symbol equations also give detail about whether a substance is a solid, liquid, gas or is in solution (aqueous) through the presence of state symbols: (s), (l), (g) or (aq).

How to use structure strips

Structure strips are a type of scaffolding you can use to support learners to retrieve information independently. Use them to take an overview at the start of the topic, to activate prior knowledge, or to summarise learning at the end of a teaching topic. For more ideas on how to use structure strips with your learners, visit 5 ways to use structure strips effectively. 

Structure strips have sections containing prompts, sized to suggest the amount that learners must write. Learners glue the strips into the margin of an exercise book and write their answers next to the sections, in full sentences. When learners have finished using the structure strip, they should have an A4 page set of notes and examples.

The strips are printed five to a page and will need to be trimmed to size. Find them on the second page of the student sheet.

Scaffolding

• Encourage learners to use the suggested key words and phrases in their answers.
• To further support learners, include additional prompts in the structure strip. If learners are struggling to engage with the task, supply them with sentence starters created from the model answers.
• As learners grow in confidence, ask them to attempt the extension question first and then use the structure strip to improve or self-assess their answer.

Key words

Balanced symbol equation, word equation, reactants, products, chemical formula, conservation of mass, balancing number. 

Metacognition

This resource supports learners to develop their metacognitive skills in three key areas.

• Planning: the strips provide scaffolding to plan the written response. Learners will decide where to gather information from (textbooks, own notes, revision websites). Ask learners: is the source of information you are using reliable?
• Monitoring: learners are prompted by the questions in the structure strip and can check their own answer against the prompts. Ask learners: have you covered all of the prompts in the space provided? Do you need to change anything to complete the task?
• Evaluation: learners can self-assess or ask a peer to check their work against the answers. Ask learners: did you achieve what you meant to achieve? What might you do differently another time?

Answers

Suggested answers for the structure strip activity are given in the downloadable teacher notes.

Answers to extension question

The number of hydrogen, chlorine and oxygen reactants and products are all correct in the table. However, the number of calcium atoms in the reactants column is wrong. In the formula for the subscript ‘2’ only refers to the elements in the brackets. A correct table tally is available in the teacher notes.

Balanced symbol equations show how mass is conserved by balancing the equation.

The incorrect equation included in the learner question is:

 HCl + Ca(OH)₂ → CaCl₂ + H₂O

The correct balanced equation is below:

 2HCl + Ca(OH)₂ → CaCl₂ + H₂O

To balance the equation, learners need to add a large ‘2’ before . This means they now have four hydrogens and two oxygens in the products. Learners then need to add a ‘2’ in front of hydrogen chloride to mean that they now have four hydrogens in the reactants and two chlorines in the products. The equation is now balanced and mass is conserved.