There are a number of steps in the treatment of water to ensure supplies are clean and safe.

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1 ExamLearn.ie Water

2 Water The water cycle 1. Heat from the sun causes water to evaporate from seas. 2. As water vapour rises it cools. Condensation produces clouds of tiny droplets of water. 3. Cloud rises and further cooling occurs. Drops of water become heavier and fall as rain. 4. Water collects in streams and rivers 5. Rivers flow to the sea; they dissolve substances from rocks and receive sewage and industrial waste. 6. Some water is diverted to reservoirs. 7. The water is purified in water treatment works. It is the used in homes and industry. 8. After use it is treated in sewage works. 9. It is then returned to rivers and sea. Properties of water: The freezing point is 0 degrees celcius and boiling point is 100 degrees celcius. Water expands as it freezes. The density of water is 1g/cm 3. Water is an excellent solvent. Tests fro presence of water: water turns blue cobalt chloride paper pink and white anhydrous copper sulfate blue. Water tends to cling o glass. The attraction of water to glass explains the shape of the meniscus of water in a measuring cylinder, the water surface is not flat as the water is attracted to the sides of the glass. Water Treatment There are a number of steps in the treatment of water to ensure supplies are clean and safe. 1. Screening stage involves passing water through wire mesh to remove floating debris like plastic bags. 2. Settling water flows into settling tanks. As water flows into tanks, aluminium sulfate is added to take cloudiness out of water. The cloudiness in water is caused by small particles suspended in water.

3 3. Filtration water passed through filter beds with layers of sand and gravel, to ensure not even the smallest particles of dirt stay in the water. 4. Chlorination chlorine is added to water to kill bacteria in water. This process is called disinfecting or sterilizing the water. 5. Fluoridation compounds of sodium fluoride are added to help reduce tooth decay. Mandatory Experiment *To show presence of dissolved solids in sample of water Apparatus required: clock glass, Pyrex beaker, hot plate, tongs, water Method 1. Set up apparatus Pyrex beaker with boiling water on hot plate, clock glass on the beaker with he tap water in it. 2. Bring the water in beaker to boiling point. Note steam produced, evaporates tap water from clock glass. 3. Turn off heat when all water in clock glass evaporated. 4. Using tongs, remove clock glass from beaker. Result Solid material left on clock glass Conclusion Material must have been dissolved in the tap water. In many cases, these dissolved substances add a refreshing taste to the water. Hard and Soft Water Hard water us water that does not easily form a lather with soap. Soft water does form a lather easily with soap.

4 The hardness of water was caused by the presence of calcium and magnesium ions. These ions combine with soap ions to form insoluble calcium compounds. These compounds are the scum that is formed in the water. Hard water is generally found in limestone areas. The chemical name for limestone is calcium carbonate. Limestone does not dissolve in water, so how do calcium ions get into the water? The answer lies in the fact that rainwater is slightly acidic. Rainwater is acidic because carbon dioxide in air dissolves in water to give acidic solution. The acidic rainwater reacts with the insoluble calcium carbonate and changes it to soluble calcium hydrogencarbonate, which then dissolves in water and gives rise to the calcium ions that cause hardness. Mandatory Experiment *To test samples of water for hardness Apparatus required: rack of test tubes, soap flakes, water samples (rain water, tap water, seawater, distilled water, hard water) In this experiment, the hardness of water samples is compared. We add soap flakes to water, small amount at a time until water gives a lather. The harder the water, the more soap flakes are required to give a permanent lather. Method 1. Add same amount of water from each samples to test tubes. 2. Add soap flake to each test tube. 3. Put thumb over test tube and shake each test tube for a few seconds. Put each tube back and wait 20 seconds. If a lather remains after this time, we say one soap flake was required. 4. If lather does not remain, add more soap flakes and shake agin, wait 20 seconds. 5. Continue this way and record number of soap flakes required to produce a permanent lather. Result Each water sample requires different number of soap flakes to form a permanent lather. Conclusion The water sample that needs most soap flakes is the hardest. The water sample that

5 needs least soap flakes is the softest. Removal of Hardness A number of methods may be used to remove the hardness from water, such as boiling and ion exchange. Boiling this removes hardness due to calcium hydrogencarbonate only. Boiling the water converts soluble calcium hydrogencarbonate into insoluble calcium carbonate. Thus, the calcium ions are removed. Ion Exchange Ion exchange resins have the ability to swap ions that cause hardness with ions that cause softness. It swaps calcium and magnesium ions in the water for sodium ions. Therefore, the water has been softened. Hard water advantages: 1. Provides calcium for teeth and bones 2. Nicer taste

6 3. Good for brewing and tanning Hard water disadvantages: 1. Blocks pipes, leaves scale on kettles 2. Wastes soap 3. Produces scum Splitting water into its elements When electricity is passed through water, chemical reaction occurs. A little sulfuric acid is added to water to help it conduct electricity. An electric current is passed through the water using a Hofmann voltameter or using test tubes. This splits the water into hydrogen and oxygen gas. The volume of hydrogen is twice that of oxygen, Therefore, we represent water by the formula H 2 O. The Hofmann voltameter contains two pieces of platinum metal. Platinum must be used, as it does not react with the acid added to the water. These two pieces of platinum are connected to the battery. The results An electric current is allowed flow for few minutes through the voltameter. It is found that two gases are formed. Oxygen forms at the positive electrode of battery (test with glowing splint). Hydrogen forms at the negative electrode (burns with a pop).

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8 Electrolysis: The electric current is causing a chemical reaction to occur. Water is being broken down into the elements hydrogen and oxygen. The production of a chemical reaction using electricity is called electrolysis.