Acid-Base Titrations: Calculations and Methods
This page provides a comprehensive overview of acid-base titrations, covering key definitions, calculation methods, practical procedures, and techniques for reducing uncertainties. It is designed to help A-level chemistry students master both the theoretical and practical aspects of titrations.
Key Definitions
The page begins by defining essential terms used in acid-base titrations:
Vocabulary: A standard solution is a solution with a known concentration.
Definition: Acids are proton donors that produce H+ ions, while alkalis are proton acceptors that produce OH- ions.
The difference between weak and strong acids is explained, noting that weak acids partially dissociate while strong acids fully dissociate.
Vocabulary: The endpoint of a titration is reached when the two solutions have fully reacted, typically indicated by a color change in the indicator.
Calculation Methods
The document provides detailed examples of titration calculations for determining unknown concentrations and molar masses:
Example: A problem involving 25.0cm³ of 0.150moldm³ sodium hydroxide reacting with 23.40cm³ of sulphuric acid is used to demonstrate how to calculate the concentration of H₂SO₄.
The solution is presented in a step-by-step manner, illustrating how to:
- Calculate moles of the known substance (NaOH)
- Find moles of the unknown substance using the molar ratio from the balanced equation
- Calculate the concentration of the unknown substance (H₂SO₄)
A similar approach is used to demonstrate calculations for determining unknown molar mass.
Titration Procedure
The page outlines the titration method step by step for A Level students:
- Use a pipette to add 25cm³ of acid to a conical flask with a few drops of indicator
- Pour alkali into the burette and record the initial volume
- Perform a trial titration, swirling the conical flask and stopping when the endpoint is reached
- Repeat titrations to obtain concordant results (within 0.1cm³)
Highlight: The importance of obtaining concordant titres is emphasized for accurate results.
Reducing Uncertainties
The document provides valuable advice on reducing uncertainties in chemistry titrations:
Example: To reduce burette reading uncertainty, students are advised to increase the titre volume by either increasing the volume or concentration of the substance in the conical flask or decreasing the concentration of the substance in the burette.
The importance of washing the conical flask between titrations to avoid contamination is also stressed.
Creating Accurate Results Tables
The page concludes with guidance on creating accurate titration results tables for chemistry studies:
Highlight: All results should be recorded to two decimal places, including zero readings.
An example table is provided, showing how to properly record rough and concordant runs, with notes on identifying and discarding anomalous results.
This comprehensive guide equips students with the knowledge and skills necessary to perform accurate acid-base titrations and calculations, preparing them for both practical lab work and theoretical exam questions.
