Hard and Soft Water

Hard and Soft Water
Hard water is made when water runs over or through landscape containing calcium ( Ca ) and magnesium (mg ) ions. These materials dissolve into the water making it hard. If rain water falls on limestone or chalk ? CaMg (CO ) (this is the common form of limestone which contains both ca and mg ions. Some forms of limestone contain only one of these materials but the result is just the same) then the carbonic acid present causes a reaction Ca CO +H CO Ca (hco ) MgCO + H CO My(hco ) Calcium Hydrogen carbonate and magnesium hydrogen carbonate [Ca(H(O ) ] isn?t strongly soluble in water and therefore it forms temporary hard water. If rain water falls on gypsum (calcium sulphate) then the gypsum dissolves to make a solution known as hard water: Ca SO +H O Ca (hso ) Properties of hard water ======== Water has a layer on top of it known as surface tension, here there are weak van-der-wall forces that hold the molecules together, making a weak curved effect. This layer is unreactive and also makes it impossible for soap to react with the water to form lather. In permanent hard water this layer cannot be broken by soap and therefore will not react with it but will form a layer of scum. The lower the concentration of hard water the softer the layer will be and therefore it will be easier for the soap to react with the water to form lather.
This is due to the absence of Ca and my ions. Hardness of water is defined by the concentration of Ca and mg ions in the water. Hardness (mg /l 2.5 ( concentration of Ca (mg(L)+4.1 (cone of mg (mgl) The classification of hard water concentration falls into five categories. Hardness Concentration Soft water Slightly hard water Moderately hard water Hard water Very hard water 0 to 1 grain /gallon 1 to 3.5 grains/gallon 3.5 to 7 grains/gallon 7 to 10.5 grains/gallon over 10.5 grains/gallon Hard water Hard water affects most households; pipes can become clogged with lime scale or fur (a deposit of calcium or magnesium). The heating element in a kettle would be covered in scale if left untreated for a length of time. This will insulate the element and it will eventually burn itself out. A copper boiler with a thick layer of lime scale inside it will eventually melt because the heat isn?t being transferred to the water properly. The harder the water the harder it becomes to clean anything in it. More and more soap or detergent is needed to build up a sufficient lather and clothes washed in hard water look dull and colourless. There is no risk in drinking hard water, in actual fact it aids growing bones and teeth in children and reduces the risk of heart disease. Soft water Soft water contains little or no mg or Ca ions. Soap lathers easily in soft water and no scum will form. It will not leave lime scale on kettles or other household appliances but it has its disadvantages. The lack of lime scale in the water is damaging to people?s health, leaving people with more brittle bones and prone to heart problems in later life. Pipes will erode quickly as there is no protective layer of lime scale. Scum Scum is formed when soap reacts with the mg and Ca ions in hard water to form calcium and magnesium salts. These coat the outer layer of the soap and therefore stops it reacting with the water to form lather. 2R ? COONa + Ca Ca (R ? coo) 2Na Soap Soap molecules consist of carbon, hydrogen and oxygen and have two parts to them ? a ?head? and a ?tail?. The head section is made from carboxyl that attracts water to it (known as hydrophilic) and a tail part that repels water but attaches to oil and grease ( action known as hydrophobic). Water naturally groups on the surface of the skin in beads because of surface tension. When soap comes into contact with the skin the ?tail? end repels from the water, whilst the ?head? is attracted to it. This causes the film of water to be broken so it can now stick to the skin. The hydrophobic ?tail? end of a soap molecule attaches itself to the oil and grease (secreted by the body to protect it from the environment) on the skin and detaches itself from the skin taking the oil, dirt and grease with it. O The molecular R-C structure of soap O-Na Advantages 1. Soap does not often damage the skin 2. It cleans most types of common dirt. Disadvantages 1. It does not remove some types of dirt well. 2. Scum that is formed stops the lathering with hard water Removing hardness from water Temporary hard water (so called because its removal is reversible) can be removed by one of Three methods. 1.Boiling: Ca CO H O CO Ca (hco ) With this method an insoluble ppte forms (CaCO ) otherwise known as scale or fur. As the Ca is in the ppte the water is now soft. This is known as Distillation. 2.Water Softeners The most used water softener is NaCO (soda crystals) Ca (hco ) Na CO 2NaHCO +Ca CO The (n ions react with the soda crystals and forms the insoluble CaCO 3.Sequestration This method does not remove the Ca ions but reacts with them, forming a complex molecule that cannot react. In domestic situations poly phosphates are used, containing the ion P O (commonly known as calgon). My aim and method I will investigate how, as the volume of soap increases, the volume of lather produced from the reaction increases. I will examine the effects of changing the amount of soap soln. in the water, as well as testing different Molar of hard water. I will try to discover relationships between the Molar of the water and how it reacts with soap in different quantities. Method In order to obtain valid results I will need to conduct a fair test; I will do this by keeping certain details of the practical constant i.e. the water amount. I will also be keeping to a set method. 1.pour into a 250ml measuring cylinder 50cm g one mole of conc. (any of; 0.0, 0.002, 0.004, 0.006, 0.008 and 0.01) of hard water. 2.add a certain amount of soap soln. From the range (5cm ,10cm ,15cm 20cm 25cm ) 3.attempt to shake mixture a certain amount of times at a constant rate and force. 4.measure and note down the resulting amount of lather, if any in terms of volume. 5.empty and clean measuring cylinder thoroughly 6.repeat Apparatus (equipment) 1. 250ml measuring cylinder 2. large amount of soap soln. 3. large amount of permanent hard water 4. large amount of temporary hard water 5. large amount of soft water Predictions Soft water (conc. 0.0) As there are no Ca or my ions in this water type a large amount of lather will be produced. As the soap volume increases so will the lather volume. Predicted Graph Slightly hard water (conc. 0.002) As there is a small amount of Ca and my ions present in this concentration I would expect there to be not much of a change in the amount of lather produced but there will be slightly less than there was for soft water. Predicted Graph Harder water (conc. 0.004) As before there will be less lather made by the reaction because the calcium and magnesium ions will create a film over the water surface, creating a small amount of scum before the soap reacts with the water and forms lather Predicted Graph Hard water (conc. .0.006) I think that there will be very little lather produced in the first few tests. This will change by the time the soap volume has increased to 25cm Predicted Graph Quite hard water (conc. 0.008) I predict that at first there will be no reaction due to the Ca and my ions in the water and only scum will form until the third or fourth test. Predicted Graph Very hard water (permanent hard water -conc. 0.01) I predict that there will be even fewer reactions and less lather than any other experiment Predicted Graph I will obtain these different concentrations by mixing the 4 different types of water together; 0.0 = 50cm soft water 0.002 = 40cm soft water +10cm hard water 0.004 = 30cm soft water +20cm hard water 0.006 = 20cm soft water +30cm hard water 0.008 = 10cm soft water +40cm hard water 0.01 = 50cm permanent hard water Evaluation == Except for one or two problems the practical results are fairly reliable; they prove my original basic hypothesis that ?more soap with the water = more lather, but the higher the conc. of the hard water, the less amount of lather is produced with the same amount of soap?. Proving this hypothesis is about all the results are useful for, because there are so many factors that interfere with the graph points that they render the actual lather amounts noted down un-applicable, leaving only the shape of the graph curves usable. The factors that affected the experiment were as follows ? The cheap school apparatus used was unreliable and inaccurate, along with the difficulty of asserting a precise volume of the lather. ? The heat of the soap soln varied wildly and was never the same temperature and some of the experiments were done at different times of the day, meaning that the weather interfered with the temperature of the materials used. Hot soap solution changed the results dramatically, as the molecules in any material are always vibrating; hot soap soln would be vibrating much, much more, giving it slightly different properties, such as, expanding and giving me comparatively less soap soln (I measure out the solutions in centimetres cubed). ? I am not a machine; therefore I cannot perform a perfect practical each and every time. In each experiment the force and duration of my shaking of the mixtures varied, when I became tired after an hour of shaking the water and soap the results became unreliable. I also couldn?t cover the top of the measuring cylinder entirely and the mixture occasionally spilt, altering the out come Placing the The second graph that I have drawn takes the fifth point in each curve out of the first graph, showing plainly that the amount of lather produced by the reactions decreases steadily in direct proportion to the increased concentration of the hard water. In conclusion ===== If I were to improve the tests, to make them more accurate I would buy more accurate apparatus, i.e. measuring cylinders and heatproof containers (i.e. thermos flasks to keep the liquids at a constant temperature until needed). I would do the tests on one day, or at the same time of day spread over several days so that the heat difference wouldn?t be too great. I would avoid doing the tests on Mondays or Fridays, mornings and evenings, as it is likely that I either be tire, not concentrating on the task at hand, or both. If I could I would use a machine to mix the soap soln and water, as it would do it accurately each time and I would also ensure that the concentration of the hard water stayed constant.

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