Solving a Problem by Intentional Circular Reference

When a formula refers to itself, either directly or indirectly, it creates a circular reference. If a circular reference occurs. Excel issues a Cannot resolve circular references message and displays a zero value in the cell. 

Usually circular references occur unintentionally, because the user incorrectly entered a cell reference in an equation. But occasionally a problem can be solved by intentionally creating a circular reference. 

Another example of a problem that can be solved by intentional circular reference and iteration is the calculation of the pH of a solution of a weak acid. Combining the equations for mass balance and K, we obtain the following equation for the [H ] of a weak acid of concentration C mol/L. 

Provided the extent of dissociation is small (i.e., [H ] Q, the [H ] term can be neglected and the equation reduces to  

Choose Options...from the Tools menu and choose the Calculation tab. Check the Iteration box and enter 0.000001 in the Maximum Change box. 

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