Concentration of phenol red: C1V1 = C2V2.

[Ind-] = (Concentration of phenol red × O.D. of buffer 1 at 555nm) ÷ peak O.D. at λMAX.

[Hind]: Concentration of phenol red - [Ind-].

Concentration ratio = [Ind-] ÷ [Hind].

pKa = pH - log([Ind-] ÷ [Hind]).

The standard deviation of a collection of numbers is a measure of how near they are to the mean.

The points with a low standard deviation (less than 1) are more crowded around the mean, whereas those with a high standard deviation (more than 1) are spread out further.

A low standard deviation indicates that the results are closer to the mean and that the pKa values are stable.

An isosbestic point in spectroscopy is the wavelength at which the entire absorbance of the sample is unaffected by chemical or physical processes.

This may be shown on a graph as the intersection of the optical densities of the two forms of phenol red, since 480 nm is the wavelength at which the absorbance is independent of pH, making it the isobestic point.

Holding the cuvette with bare hands may have resulted in fingerprints on the glass, which fractures the light being projected in a spectrophotometer.

Errors might arise if the spectrophotometer is not properly calibrated before to the experiment.

Errors can arise due to incorrect cuvette positioning in the spectrophotometer, which stops light from shining through the solution unscathed.

Poor mixing procedures used to test the solutions might cause errors.

When the spectrophotometer is not calibrated to zero with distilled water, errors might arise.