Delloyd's Lab-Tech Chemistry


Determination of chloride in sea water by Ion Selective Electrode


MV / Ion meter, chloride electrode (combination), magnetic stirrer, stir bar, stir bar retriever, stop watch.


Volumetric flasks 100ml; Pipettes grad; 1ml, 2ml, 5ml, and 10ml; beakers 250ml, 100ml.

Sample: Sea water. Use 1 ml per 100 ml volume.


Sodium chloride, NaCl, FW = 58.44
Sodium nitrate, NaNO3, FW = 84.99

Solutions preparations:

1. 1M NaCl. Dissolve 58.44 g of the salt in 1 liter distilled water, and store in a polythene bottle.
2. ISA. (Ionic Strength Adjuster) = 5M NaNO3
Dissolve 424.95 g in one liter distilled water.

Analytical notes:

1. Make up sample in triplicate. 1 ml in 100 ml vol.
2. Can use a 2% NaCl solution as a substitute for sea water.
3. Do a four-point calibration of meter, and measure from lowest concentration to the highest concentration. eg 10-5M to 10-1M
4. Activity / response measurements. Make up and measure stds, with ISA (2 mls.)
5. Prepare blank with ISA (2 mls) and distilled water only.
6. Chloride molarity to ppm:
10-1 = 3550ppm = 0.58% Na Cl
10-2 = 355ppm = 0.058% NaCl
10-3 = 35.5ppm = 0.0058% NaCl
10-4 = 3.55ppm = 0.00058% NaCl

Operation of Instrument:

Follow Users Guide: obtain help and advice from Demonstrator or Technician