PASCO PS-2195 Salinity Sensor - Manual (Page 9)

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Model No.PS-2195 Notes on the Experiment
9
Notes on the Experiment
If bubbles form inside the probe, the conductivity reading will be reduced because the
bubbles will form an insulating later on one or both of the electrodes. One way to
eliminate the bubbles is to tap the probe. Another way is to increase the speed of the
magnetic stirrer to allow more solution to flow through the probe.
If time is limited, prepare the solutions before the period begins.
Data Table
Data Analysis
The table lists typical experimental results. In general, ionic salts at low to moderate
concentrations have a temperature dependence of 2% per degree at 25 °C. Acids,
bases, and concentrated salt solutions have somewhat lower values, typically 1.5%
per °C. In contrast, ultra pure water has a much larger value; 5.2% per °C.
Questions
1. The conductivity increases linearly with temperature over the observed tempera-
ture range.
2. The slopes are approximately equal for all the solutions.
3. Temperature, concentration, and solubility will affect the conductivity of a solu-
tion.
Solution percent change/ °C at 25 °C
0.1% NaCl (1000 ppm) 2.1
0.4% NaCl (4000 ppm) 2.0
0.005 M NaOH (1000 ppm) 1.9