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If using a meter with millivolt readout only
1. Adjust the meter to measure mV.
2. Measure 50 mL of the more dilute standard into a 150 mL
beaker. Add 5 mL carbon dioxide buffer. Stir thoroughly.
3. Rinse electrodes with distilled water, blot dry and place into the
beaker. When a stable reading is displayed, record the mV value
and corresponding standard concentration.
4. Measure 50 mL of the more concentrated standard into a second
150 mL beaker. Add 5 mL carbon dioxide buffer. Stir thoroughly.
5. Rinse electrodes with distilled water, blot dry and place into the
second beaker. When a stable reading is displayed, record the
mV value and corresponding standard concentration.
6. Using semilogarithmic graph paper, prepare a calibration curve
by plotting the millivolt values on the linear axis and the standard
concentration values on the logarithmic axis.
7. Measure 50 mL of the sample into a 150 mL beaker. Add 5 mL
carbon dioxide buffer. Stir thoroughly.
8. Rinse electrodes with distilled water, blot dry and place into the
beaker. When a stable reading is displayed, record the mV value.
9. Using the calibration curve prepared in step 6, determine the
unknown concentration.
