Topic Three (1.3): Empirical and Molecular Formulae, Moles and the Avogadro Constant

Introduction

We need to be able to predict the amounts of substances involved in chemical reactions. Production of ammonia in a chemical plant would be a very wasteful process if we did not mix the right quantities of nitrogen and hydrogen gas. This section builds on your IGCSE knowledge and forms the basis of all calculations throughout the course. You should be confident at rearranging equations and working out ratios. If you are not, refer back to the Student Maths guide before starting this section.

Reading

Edexcel AS/A Level Chemistry Student Book 1 pages 16 to 39

Edexcel International A Level Chemistry Lab Book pages 6 to 8

Tasks

Complete the following:

• Read pages 16 to 17, making appropriate notes.
• Complete the ‘checkpoint’ questions.
• Make sure the definitions (subject vocabulary) and equations are clearly written out on revision cards.

WATCH – Moles (YouTube) Links to an external site.

• Read pages 18 to 37, making appropriate notes.
• Complete the ‘checkpoint’ questions.
• There are plenty of worked examples of calculations which you should review with care and ‘subject vocabulary’, which needs to be added to your revision cards.

COMPLETE – Gridlocks: Concentration of Solutions 1 (RSC) Download COMPLETE – Gridlocks: Concentration of Solutions 1 (RSC)

COMPLETE – Gridlocks: Concentration of Solutions 2 (RSC) Download COMPLETE – Gridlocks: Concentration of Solutions 2 (RSC)

COMPLETE – Gridlocks: Volume of Gases (RSC) Download COMPLETE – Gridlocks: Volume of Gases (RSC)

COMPLETE – Gridlocks: Moles Equations (RSC) Download COMPLETE – Gridlocks: Moles Equations (RSC)

REVIEW – Worked Examples: Calculations Download REVIEW – Worked Examples: Calculations

 Practical Knowledge

Introduction to Core Practical 1

WATCH – Collecting Gases Video Clip 1 (YouTube) Links to an external site.

WATCH – Collecting Gases Video Clip 2 (YouTube) Links to an external site.

• The first clip is the same method (vinegar = ethanoic acid and baking soda is sodium hydrogen carbon).
• The second clip is a more accurate way of measuring released gases and is more suitable for monitoring rates.

REVIEW & COMPLETE - Core Practical 1 Exercise (Measure the Molar Concentration of a Gas) Download REVIEW & COMPLETE - Core Practical 1 Exercise (Measure the Molar Concentration of a Gas)

REVIEW - Core Practical 1 Answers Download REVIEW - Core Practical 1 Answers

• It is especially important that you can draw a good diagram of the apparatus.
• You can use this data to complete CORE PRACTICAL 1 in your Chemistry Lab book (pages 6 to 8).

WATCH – Water of Crystallisation (YouTube) Links to an external site.

WATCH – Making Nickel Sulphate (YouTube) Links to an external site.

REVIEW & COMPLETE – Practical Exercise 1.1 (Make a Salt and Calculate the Percentage Yield of Hydrated Nickel Sulphate) Download REVIEW & COMPLETE – Practical Exercise 1.1 (Make a Salt and Calculate the Percentage Yield of Hydrated Nickel Sulphate)

REVIEW - Practical 1.1 Answers Download REVIEW - Practical 1.1 Answers

WATCH – Double Salt Preparation (YouTube) Links to an external site.

REVIEW & COMPLETE – Practical Exercise 1.2 (Make a Salt and Calculate the Percentage Yield of Ammonium Iron (ii) Sulphate) Download REVIEW & COMPLETE – Practical Exercise 1.2 (Make a Salt and Calculate the Percentage Yield of Ammonium Iron (ii) Sulphate)

REVIEW - Practical 1.2 Answers Download REVIEW - Practical 1.2 Answers

Top Tips

Make sure that you understand the following key points:

• Always use the periodic table that you can download from canvas or from your textbook.
• If you are doing a multi-step calculation only round at the final stage. Carry forward all the answers on your calculators.
• Remember quantities are given to two decimal places you must also work to two decimal places. This means that the mass is 2.30 grams NOT 2.3 grams.
• You may be asked for significant figures OR decimal places so take note of this. If asked a mark will be lost if you fail to do this. If not asked you can show your answer with a sensible number.

Key Terms

Add the following subject vocabulary with definitions to your glossary.

• Molar mass
• Avogadro’s constant
• Mole
• Hydrate
• Theoretical yield
• Actual yield
• Percentage yield
• Atom economy
• Empirical formula
• Molecular formula
• Molar mass
• Molar volume
• Solute
• Solvent
• Solution
• Mass concentration
• Molar concentration
• Parts per million (ppm)

Tasks

Complete the following:

• Complete the Exam Practice on pages 38 to 39.

COMPLETE – Exam Practice Calculations Download COMPLETE – Exam Practice Calculations

REVIEW – Exam Practice Calculations Answers Download REVIEW – Exam Practice Calculations Answers

REVIEW – Learning Outcomes for Module One Download REVIEW – Learning Outcomes for Module One

• Use this as a checklist to assess your knowledge.

Assignment

When you have completed all the activities and are fully prepared and feel confident with the material, you should complete Assignment One and submit it to your tutor via Canvas for marking and feedback.