Concentration & Volume Calculations | A-level Chemistry | OCR, AQA, Edexcel

Introduction

This tutorial provides a comprehensive guide to understanding concentration and volume calculations in A-level Chemistry. It covers essential concepts, formulas, and practical examples to help you grasp how to calculate the concentration of solutions and the number of moles of solute present.

Step 1: Understand the Concept of Concentration

• Concentration is defined as the amount of solute that is dissolved in a given volume of solvent.
• The formula used to calculate concentration is:
  • n = Number of moles of solute (mol)
  • c = Concentration of the solution (mol/dm³)
  • V = Volume of the solution (dm³)

Practical Tip

• Remember that 1000 cm³ equals 1 dm³. This conversion is crucial when working with volume measurements.

Step 2: Learn the Difference Between Concentrated and Dilute Solutions

• Concentrated Solutions: These contain a large amount of solute per dm³ of solvent.
• Dilute Solutions: These contain a small amount of solute per dm³ of solvent.

Common Pitfalls

• Misunderstanding these terms can lead to errors in calculations. Ensure you identify whether a solution is concentrated or dilute before performing calculations.

Step 3: Perform Concentration Calculations

To find the number of moles of solute in a solution, use the formula:

• n = c × V

Example Calculation

Calculate the number of moles in 10 dm³ of a 2 mol/dm³ solution.

1. Identify the values:
   • c (Concentration) = 2 mol/dm³
   • V (Volume) = 10 dm³
2. Plug the values into the formula:
   • n = 2 mol/dm³ × 10 dm³
   • n = 20 moles

Practical Advice

• Always double-check your units to ensure they align with the formula requirements.

Step 4: Practice with Exam Style Questions

• Familiarize yourself with the types of questions you may encounter in exams related to concentration and volume calculations.
• Practice problems that require you to calculate either the concentration or the number of moles based on given data.

Conclusion

In summary, understanding concentration and volume calculations is essential for success in A-level Chemistry. Remember the key formula ( n = c \times V ) to determine the number of moles in a solution. Practice with various problems to reinforce your understanding, and pay attention to the differences between concentrated and dilute solutions. For further study, consider reviewing exam-style questions to prepare effectively for assessments.