When calibrating a pH meter, the buffers must be at least how many pH units apart?

The requirement for buffers to be at least 2 pH units apart when calibrating a pH meter is vital to ensure accuracy and reliability in measurements. This distance minimizes the potential for measurement error and helps the meter achieve a better linear response across the range of pH values.

By using buffers that are spaced out by 2 pH units, the calibration process allows the pH meter to correctly interpolate values between those buffer points. For example, if a meter is calibrated with buffers at pH 4 and pH 6, it can effectively determine the pH of solutions around these values, ensuring more precise readings.

Using buffers closer together does not provide sufficient range to establish an accurate calibration curve, as the meter may not function correctly in the environment of the buffer solutions or may not account for non-linear responses in certain ranges. This is particularly important when measuring solutions with a pH that may fall significantly outside the range of closely spaced calibration points.