How to Determine the Concentration of a Limewater Solution
- 1). Dilute the limewater solution prior to analysis with the hard-water testing kit. Most test kits only analyze hardness up to about 500 ppm CaCO3, whereas a saturated limewater solution could possess a hardness in excess of 2,000 ppm. Therefore, pour 1 oz. of limewater solution into an 8-oz. measuring cup and then add distilled water to a final volume of 5 oz.
- 2). Follow the test kit manufacturer's instruction for measuring the hardness of the limewater sample by substituting the limewater for tap water. Typically, this involves placing a measured amount of sample into a small bottle, adding an indicator solution to the sample that changes color to let you know when the analysis is complete, and the titration solution itself. Add the titration solution dropwise and count the number of drops required to make the sample change. The instruction manual will provide the necessary information to correlate the number of drops to the hardness in parts per million calcium carbonate or grains of calcium carbonate per gallon.
- 3). Convert the result from the hardness analysis to ppm if it was determined in grains per gallon by multiplying the result by 17.1. For example, a result of 22.1 grains per gallon converts to 22.1 * 17.1 = 378 ppm. This represents the calcium content as milligrams of calcium carbonate per gallon of water.
- 4). Convert milligrams of calcium carbonate per liter to milligrams of calcium hydroxide per liter by multiplying the previous result by 0.74. Continuing the previous example, a calcium carbonate content of 378 ppm is equivalent to a calcium hydroxide content of 378 * 0.74 = 280 ppm Ca(OH)2.
- 5). Determine the ppm of the initial limewater solution by multiplying the ppm Ca(OH)2 by 5. This step compensates for the 1:5 dilution of the original sample prior to the analysis with the hard-water test kit. For the previous example, 280 ppm x 5 = 1400 ppm Ca(OH)2. This represents the concentration of the limewater solution in parts per million.
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