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Investigating how the concentration of a the metal ion affects the hardness of water.

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Introduction

Investigating how the concentration of a the metal ion affects the hardness of water Introduction Causes of hard water Almost 60% of people live in hard water areas. As the rain falls, it reacts with the carbon dioxide in the air to form carbonic acid (1). The rain then falls into streams and as it passes through rocks and soil, the carbonic reacts with minerals. One example of this is limestone; the carbonic acid reacts with calcium carbonate to form calcium hydrogen carbonate (2). This ionic compound in water, separates into calcium ions and hydrogen carbonate ions(3). These calcium ions are what make water hard. Another rock, which causes hard water, is dolerite. It is a fine-grained igneous rock. 1) H2O + CO2 H2CO3 Water +Carbon Carbonic acid Dioxide 2) H2CO3(aq) + CaCO3(s) Ca(HCO3)2 (aq) Carbonic acid + limestone Calcium hydrogen carbonate 3) Ca(HCO3)2 (aq) Ca2+(aq) + 2HCO3-(aq) Calcium hydrogen calcium ions + hydrogen carbonate ions Carbonate Soap One way of testing for hard water is to see its reaction to soap. Soft water will form a lather, but hard water will form a scum, with solid pieces floating around. Soap is sodium stearate, and all sodium compounds dissolve into water. Soap has two parts, a head and a tail. The tail is said to be hydrophobic (water hating). The head on the other hand is hydrophilic (water loving). The tail of the soap, attaches itself to the dirt, as it is trying to avoid the water, while on the other hand the head is staying in the water. The dirt is then pulled off the object as it is rinsed again. ...read more.

Middle

The funnel must then be taken out of the top as there will be a drop of soap solution at the bottom of the funnel and to prevent inaccuracies, this must be taken out. A beaker must then be put under the burette and the tap must be opened to fill the capillary. This must be done, so that the initial reading is accurate. Then, the soap solution must be discarded to prevent any contamination. The following values of distilled water and Calcium ion solution will be put into the conical flask: Volume of Calcium Ion solution in cm3 Volume of distilled water in cm3 Total volume of solution in cm3 25 0 25 20 5 25 15 10 25 10 15 25 5 20 25 0 25 25 Distilled water must be used as this experiment is done to test the concentration of calcium ions and if tap water will be used, there would most likely be calcium ions in it already. Firstly the tap on the burette must be opened fully so 2cm3 of soap pours out. Then the conical flask must have a bung put into it and then must be shaken hard for five seconds. If it looks like a lather might be forming, then the amount of soap solution added will be reduced, if not then 2cm3 will be added continually. When it looks like a lather is going to form, then the soap solution will be added drop by drop. There are different types of lathers, some are for only a short time, and others are for much longer. ...read more.

Conclusion

Also, it was hard to find out when to stop adding soap to the calcium ions. This means, the lather was different each time. This meant that the lather formed was different each time and so, some of the results were too large or too small. Also, the initial and final readings were only accurate to half of the smallest measurement. This means that the results were only accurate to 0.05. To make this more accurate, a burette with more measurements could be used. Lastly, when the solution was shook, it wasn't the same each time. This could be because my arm got tired and therefore some of the results weren't shaken enough or sometimes shaken too much. To ensure that the solutions are shaken the same amount, a shaking machine could be used that shakes the solution for the same time and at the same speed. Instead of this experiment, an EDTA titration experiment could be done. In this experiment, 50cm3 of calcium ions would be put into a Erlenmeyer flask. A few drops of 1M hydrochloric acid would be added so the solution would become acidic. Then, boil the solution for a few minutes. Let the solution cool and add 4 drops of methyl red. Add 1M sodium hydroxide until the red colour disappears. Them, add 1 or 2ml of pH-10 buffer, 3 drops of Eriochrome black T indicator solution, and titrate with standard 0.01M EDTA until one drop causes the solution to turn from red to blue. Titrate slowly. Because the colour changes take place slowly, the solution should be swirled and wait a few seconds between drops as the endpoint is approached. From the amount of EDTA used, the hardness can be told. ...read more.

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