Common Water Quality Tests

pH

pH is a measurement of the hydrogen ion concentration of the water. The pure definition is :   "-log [H⁺]". The pH scale is from 0 to 14. A pH of 7 is considered neutral. pH's below 7 are considered acidic and above 7 are alkaline. pH is very important in water chemistry because it has a direct affect on calcium solubility and corrosion of mild steel or copper alloys. For example, the higher the pH, the lower the calcium solubility or the greater the scaling tendency of the water. In cooling water chemistry, pH control with the addition of sulfuric acid prevents scale formation. However, low pH increases mild steel corrosion rates. In the steam cycle, pH is an important factor in the control of corrosion.

Solubility

Solubility refers to the amount of substance that can be dissolved in a solution such as water. When the solubility level of a compound is exceeded in water, precipitation or scale deposition results. A very important point to remember is that solubility as well as other characteristics varies greatly with temperature and pressure.

Conductivity

Conductivity is a direct method of measuring the dissolved solids content of water by measuring its ability to conduct an electrical current.

Possible Experiment for students

1. Cut a piece of metal into three equal parts.  

2. Prepare three beakers of solution, (jars or drinking glasses will suffice), with different pH's.

1 could be Tap water - pH aprox. 7.2 ave., 1 could be COKE - pH aprox 4.5 to 5.0, and the last could be tap water w/ 1 TBS dish soap pH aprox. 8.0.

3. Allow metal piece to set in each jar for 2-3 weeks.  

4. Write conclusions.