We want to solve this problem using Excel. There are two ways to approach it (easily). In this first method, we will look at the circular references method: (The second method is to use matrices)
Two substances, A and B, absorb light according to the Beer-Lambert law A = ecL where e is the extinction coefficient, c is the concentration of the absorbing substance and L is the path length (0.1 dm). If both species are in solution and the absorbance at 300 nm is measured to be 3.5 and the absorbance at 500 nm is 2.3, use simultaneous equations to calculate the concentrations of A and B in the mixed solution. The extinction coefficients, e are:
* At 300 nm, e(A) = 80; e(B) = 150 units
* At 500 nm, e(A) = 52, e(B) = 100 units.
This resource explains the background to and illustrates the use of the van’t Hoff equation. Along with some details on how it can be used, there are a number of questions to try, with some hints if you need them.
Details of the resource:
some parts of this file have audio, but it is not necessary to use this if you do not have an audio source
Derivation of the van’t Hoff to two forms – one for use in experimental analysis via graphs and one for use algebraically
How to use the van’t Hoff equation to understand how temperature changes affect a reaction
Some questions to try with video/picture tips and hints
This resource sumamrises the derviation and use of integrated rate equations in kinetics. Three examples of integrated rate equations are given (zero, first and second order) along with some worked examples and questions to try. Click on the image to access the resource:
Details of Resource:
Demonstrations and downloadable PDFs of the derivations for zero, first and second order equations
Questions with demonstrated worked examples to show you how answers were obtained
This resource covers the calculations required in volumetric and mass analysis, as well as giving an outline of how to perform a titration. Click on the image to access the resource:
Details of Resource:
Outline of how to perform a titration
Worked examples on titrations in volumetric and mass analysis
Examples for you to try with feedback and answer printouts
Raoult’s Law relates the vapour pressure of a solution to a pure solvent depending on how much solute is present. It can be used, subject to some limitations, for determing the molar mass of a substance. The interactive graphic below provides an overview of the experimental technique and details how the number of moles and hence molar mass of solute can be determined. One of the steps involves algebra that students can find difficult. Click on the image below to begin:
Details of Resource
The resource includes:
An overview of the experimental method in determining vapour pressure along with the parameters that would be measured to determine molar mass of solute by Raoult’s Law
An interactive worked example where students can decide which step they would choose in each of the four main steps in the calculation
A quiz with some questions and worked solutions to test your own knowledge
Links to downloads of the experimental method and worked example pages
