Reacting masses and gas volumes | Structure strip | 14–16 years | Resource

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Use scaffolded prompts to support learners to write about reacting masses and gas volumes

Structure strips can be used to promote independent writing. In this resource learners write about masses and gas volumes using key words, describe methods for measuring gas volumes and determine theoretical and percentage yields.

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Use the editable structure strips to support learners to find or retrieve information and write independently about reacting masses and gas volumes.

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Learning objectives

Define molar volume and explain how to use this when finding reacting volumes in a gas phase reaction.
Explain how to find the theoretical and percentage yield of a product in a reaction.
Combine writing with calculations to give a full explanation of chemical concepts.

Introduction

This resource asks learners to demonstrate their thought process, rather than simply using methods they have memorised for carrying out calculations. This will help them to develop deeper understanding. It will also show them how to set out calculations more clearly in exam answers, so that an examiner can follow what they have done, and they can check their own answers more easily.

Usually, learners are introduced to reacting mass calculations using only masses first. Therefore, they often forget that finding reacting volumes in reactions that occur entirely in the gas phase is more straightforward, using Avogadro’s law. Both the scaffolded structure strips and the extended answer question juxtapose these two methods to encourage learners to recognise the differences and be ready to apply whichever best suits the context of their calculation.

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, see 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

Measuring cylinder, gas syringe, delivery tube, conical flask, mole, molar volume, theoretical yield, actual yield, percentage yield.

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?

Extended answer question

Instruct learners to answer the question after they have attempted the structure strip. The structure strip activates the required knowledge, which learners can then apply to the question.

Consider re-framing the context of this question to one that your learners are more familiar with, to empower them to unlock their existing science capital. Read more about science capita l.

Answers

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

Answer to extension question

One mole of any gas occupies the same volume at room temperature and pressure, 24dm³ or 24,000cm³. In the reaction between methane and steam, the reactants and products are all gases. Therefore, the volumes of gases used and produced will be in the same ratio as the reactants and products in the balanced symbol equation. The ratio of methane to hydrogen in the equation is 1:4. Therefore the volume of gas will also be 1:4. So to produce 240cm³ of hydrogen we need 240/4 = 60cm³ of methane.

In the second reaction, only the hydrogen is a gas, so we need to convert the volume of gas into moles in order to be able to compare this with the mass of zinc.

moles of hydrogen in 240cm³ = 240/24000 = 0.01mol

According to the balanced equation, 1 mole of zinc is needed to make 1 mole of hydrogen. Therefore, the amount of zinc needed is also 0.01mol.

mass of zinc = moles x A_r

= 0.01 x 65

= 0.65g

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