Graphical Techniques

Graphical representation is crucial in chemistry as it allows complex data sets to be visualised, analysed, and interpreted.
Graphs can reveal trends, correlations, and the degree of scatter in data, enabling predictions about values that were not directly measured.
The choice of graph type depends on the nature of the variables and the type of relationship they possess.

A line graph is typically used to represent continuous data. It is particularly useful for showing trends over time or other continuous variables.
A scatter graph or a scatter plot is used when both the dependent and independent variables are continuous. It can highlight relationships between variables.
A bar chart is used when dealing with categorical data. Each category is represented by a bar, the height of which represents the value of the data.
Histograms are similar to bar charts but are used for continuous data that has been grouped into intervals.
Pie charts are used to represent parts of a whole, showing distribution or proportions of categories.

When creating graphs, the dependent variable (the one being measured) is plotted on the y-axis, and the independent variable (the one being manipulated) is plotted on the x-axis.
The choice of scale should enable effective use of the graph area. Each axis should start at zero unless there’s a reason not to.
Title, labels, and units should be clearly indicated on all graphs.
When interpreting graphs, look for trends or patterns in the data. Trends could be linear (straight line), exponential (curve upwards), or inverse (curve downwards).
If a line of best fit is added – typically a straight line or a smooth curve – it should balance the points above and below the line.

Graphs can be used to determine the rate of reaction by plotting the change in the amount of reactants or products against time.
In titration experiments, the volume of titrant added can be plotted against the pH to create a titration curve.
In spectrophotometry, the absorbance of a solution can be plotted against wavelength to obtain an absorption spectrum.
In thermal chemistry, the potential energy of a system can be plotted against the progress of the reaction to create a reaction energy profile.