Carbon Dioxide Testing

 

Carbon dioxide concentration is typically tested in both the raw and finished water.  In the raw water, a high concentration of carbon dioxide will react with the lime being added during the treatment process.  In the finished water, carbon dioxide can contribute to corrosion in the distribution system. 
First, the operator adds a magnetic stirrer to a clean and dry 250 mL beaker. 
Next, the operator collects a 200 mL sample of finished water.  In this case, he is using a 100 mL graduated cylinder. 
He pours 100 mL of treated water into the beaker.
Next, he adds another 100 mL of treated water to reach a total sample size of 200 mL. 
The digital titrator has been filled with 0.0045 N
 sodium hydroxide.  Now the operator lowers the digital titrator delivery tube into the water sample. 
The operator turns on the magnetic stirrer, which is at the back of the side of the base.
The operator adds six drops of P-170, which is 0.5% phenolphthalein in 50% ethyl alcohol.  The sample water remains clear, which means that carbon dioxide is present in the sample. 
The counter on the titrator is set to 0.  Then the operator slowly turns the knob to inject sodium hydroxide into the water sample. 
When the sodium hydroxide has neutralized all of the carbon dioxide, the sample turns pink.  The operator waits for approximately 20 seconds to ensure that the pink color will not fade.
This deep pink color denotes the end of the carbon dioxide test. 
The operator now reads the counter on the digital titrator.  He has used 3.0 mL of titrant. 

The operator used a different sample size and a different normality of sodium hydroxide than was used in Lab 14.  So he must use the calculations shown here to determine the concentration of carbon dioxide in the sample.