Acids and bases (A-level only) exam tips

Exam tips

• Show all steps in calculations

  When calculating pKa or concentrations, clearly show each step of your working.

  This helps to avoid mistakes and allows partial credit for correct methodology, even if the final answer is incorrect.

• Use of pKa

  When comparing acid strengths, use pKa values instead of Ka values.

  pKa values are easier to interpret; lower pKa indicates a stronger acid, making comparisons straightforward.

• Show all working in calculations

  Always write down the formula used, substitute values clearly, and include units.

  This helps to avoid losing marks for calculation errors and demonstrates your understanding of the process.

• Sketching pH Curves

  When sketching pH curves, clearly label the axes and mark the initial pH, equivalence point, and regions of gradual and steep changes.

  A well-labeled sketch helps in visualizing the titration process and understanding the behavior of acids and bases.

• Practice sketching pH curves

  Regularly practice sketching pH curves for different acid-base titrations to familiarize yourself with their shapes and key features.

  Understanding the shape of pH curves helps in predicting the behavior of the solution during titrations and selecting appropriate indicators.

• Show all workings in calculations

  When performing calculations, clearly show each step, including the formula used and units.

  This helps to avoid losing marks for minor errors and demonstrates your understanding of the process.

• Always use the correct equation for buffer calculations

  When calculating the pH of a buffer, ensure you use the Henderson-Hasselbalch equation correctly, paying attention to the concentrations of the acid and conjugate base.

  Using the correct equation helps to accurately determine the pH and understand the buffer's capacity to resist changes.

• Use the Henderson-Hasselbalch equation correctly

  Always check the concentrations of the weak base and its conjugate acid before applying the equation.

  Using the correct concentrations ensures accurate pH calculations for buffer solutions.

• Show all steps in calculations

  When calculating pH, clearly show the use of the Henderson-Hasselbalch equation, including the values substituted and the final answer.

  This helps to avoid losing marks for not demonstrating understanding of the calculation process.

• Use the Henderson-Hasselbalch equation wisely

  Always check if the concentrations of the weak acid and conjugate base are provided before applying the Henderson-Hasselbalch equation.

  This equation is only applicable when you have both components in the buffer solution, ensuring accurate pH calculations.