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An investigation of the effect of concentration of a chosen ion on the ''Degree of Hardness'' of water.

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Introduction

An investigation of the effect of concentration of a chosen ion on the ''Degree of Hardness'' of water Preliminary Work I have used a previous experiment that I carried out, to help inform my plan. It is called Investigation the ions, which cause hardness of water and it, will be included in my appendix. In this experiment there were 14 different substances dissolved in distilled water. 4cm� of each one was put in a separate test tube. 30 drops of soap were then added to the solution. A bung was placed in the test tube, and the test tube was shaken. This shaking was done until either a scum or lather formed. This experiment has helped to inform my plan because it showed which metal ions I could have used. I told me that both Magnesium and Calcium ions caused a scum to form in hard water and that I could use either in my investigation. Because of this I chose calcium, as it was readily available to me. At the beginning of my coursework I will take different volumes of Calcium chloride solution and add enough soap to form a later for 10 seconds. ...read more.

Middle

This makes it better to use a large measuring cylinder for large volumes.) Distilled water(-This is pure water, and can therefore be used to clean apparatus and mix to form concentrations without contaminating them.) Bung(-This stops solution from escaping out of the conical flask. ) 0.01M Calcium chloride solution Soap solution Method Safety glasses were put on. An empty conical flask was taken and filled with 20cm� of 0.01M calcium chloride solution. The calcium chloride solution was measured in a measuring cylinder, which can contain a total volume of 20cm�. The 20cm� was measured to the bottom of the meniscus in the measuring cylinder. This gives more accuracy. This was then poured into a conical flask. A conical flask was used because a bung can be put into it. A burette was then clamped to a clamp stand. It was then filled with soap solution. The tap was turned to allow to some soap solution to run through. This got rid of any trapped air. A burette was used because it gave results accurate to � 0.1cm�, which gives greater accuracy. The reading on the burette was then measured to the bottom of the meniscus. ...read more.

Conclusion

A way of improving my experiment would be to use a stopwatch to time the 10 seconds that the lather has to form for. Counting the seconds in my head is not very accurate and this is a way of improving it. Different apparatus could also be used such as a burette marked to a higher degree of accuracy, and a volumetric pipette. A machine could also be used to control the shaking because when I did it, it was not very accurate. The machine could be set a set number of shakes, which would all be the same. This would improve the accuracy of the experiment. The burette is accurate to � 0.1cm�. The smallest volume I measured in the burette was 24.7cm�. Therefore percentage error is 0.1 x 100 =0.4% 24.7 The measuring cylinder is accurate to � 0.5cm�. The smallest volume I measured in the measuring cylinder was 4cm�. Therefore percentage error is 0.5 x 100 =12.5% 4 Therefore total percentage error is 12.9% I have added error bars to my graph. All the points no fit on the line of best fit. This shows that if I had improved the accuracy of the measuring cylinder I would improve my results greatly. The anomalies that I got could have been caused by this inaccuracy in the measuring cylinder. ...read more.

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