Experiment #10 The Chemistry of Natural Waters Lab Report Jake Shoemaker Group: 11/5/10 Chemistry 111 Section 103
Introduction: Water hardness is defined as a measure of the amount of calcium and magnesium salts dissolved in water4. Hard water is water that contains large amounts of dissolved calcium and magnesium cations, and soft water is water that little or none of the cations10. The hardness of water is important because it affects numerous aspects of our life. Water hardness has an effect on the way water tastes, it creates problems with plumbing and industries, and the water hardness has an effect on cleaning/washing10. The calcium and Magnesium that exist in the water do not taint it in any way. The hardness of water does, however, affect the way the water tastes, but different individuals have different opinions on which type tastes better. The problem of water hardness in the use of industrial water boilers/plumbing systems10 is that the water evaporates leaving behind rocklike deposits consisting mostly of calcite crystals 10. This is a problem because the calcite crystals build up and clogs pipes, blocks jet engines, etc. and is very expensive and difficult to remove, if removable at all10. Problems similar to these can be found everywhere that large volumes of natural waters are used to undergo the industry’s processes3. In washing, when hard water is used to wash away soap the soap anions react with the calcium and magnesium cations to produce a greasy scum3. There are various methods in measuring water hardness. EDTA
(ethylenediaminetetraacetic acid) titration is one method that is commonly used. EDTA titration is a chelating agent3. A chelating agent is a substance whose molecules can form several bonds
to a single cation3. An indicator is added to the sample to be tested that turns red if magnesium is present in the sample. EDTA is added after and first reacts with the calcium cations then the magnesium cations. After titration is complete, the water will turn blue. Where the titration starts can be used to determine the concentration of the calcium and magnesium cations 10. One symptom of using EDTA titration is that the EDTA will reveal to just calcium and magnesium cations, but all +2 cations10. Another method to measure water hardness is Atomic Absorption Spectrophotometry (AA). Unlike EDTA titration, AA uses an instrument called an atomic absorption spectrophotometer that uses monochromatic light that has an energy corresponding to the element of interest (in this case calcium and magnesium tested separately) 10. The atoms in the sample will absorb the light and the amount of absorbance is proportional to the concentration of the atoms in the sample3. As with EDTA titration, AA also has a drawback such that a very soft water (such as Aquafina) will not be measured correctly in the sense that negative amounts of an element are present in the reading. The fact that both methods have flaws in the measuring of calcium and magnesium cations is the reason why more than one method is used to measure hardness. By using one method, another method can then be used to confirm or disagree with the data. I predict that the Aquafina water sample I am using for my sample to be extremely soft because it is purified water. When most water goes through a purification process, the goal of the company is to remove most of the minerals and other unwanted substances from the water. I predict that the water from the Brita water sample will be soft, but not as soft as
Aquafina because the Brita water is also put through a filtration system, but a less extensive one. I predict that the water taken from the Whitmore Building water fountain right outside the classroom to be hard water because public water typically isn’t purified. Procedure: The procedure can be referenced in ChemTrek10. This is an overview of the in depth procedure: The hardness of each of our water...
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