Investigate the hardness of water in 5 different water solutions

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Chemistry coursework: Hardness of water

Planning

Aim

To investigate the hardness of water in 5 different water solutions

Background knowledge about hard water

The hardness of water is caused by the presence of Calcium 2+ and magnesium 2+ ions in the water. These minerals in water can cause some everyday problems. They react with soap and produce a deposit called "soap scum" that remains on the skin and clothes and, because it is insoluble and sticky, cannot be removed by rinsing. Soap curd changes the pH of the skin and may cause infection and irritation. It also remains on the hair making it dull and difficult to manage. Soap scum picks up the dirt from laundry water and holds it on cloth, contributing to a grey appearance of white clothes. It is especially troublesome when wash water is allowed to drain through the clothes. The use of synthetic detergents may help a little, but the active ingredient in the detergent is partially inactivated by hardness and more detergent must be used for the same cleaning task. Some detergents will produce soap during the reaction with oil or grease on the surface being cleaned and as a result they will also deposit soap curd. A ring around the bathtub and spotting on glassware, chrome, and sinks are constant problems in the presence of hard water. They require additional rinsing and wiping, increasing the time spent on everyday cleaning.

Cooking with hard water can also be difficult, producing scale on pots. Some vegetables cooked in hard water lose colour and flavour. Beans and peas become tough and shrivelled. Hard water may also shorten the life of plumbing and water heaters. When water containing calcium carbonate is heated, a hard scale is formed that can plug pipes and coat heating elements. Scale is also a poor heat conductor. With increased deposits on the unit, heat is not transmitted to the water fast enough and overheating of the metal causes failure. Build-up of deposits will also reduce the efficiency of the heating unit, increasing the cost of fuel.

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Prediction

The experiment involves measuring the height of the lather when soap is added to the 5 different types of water. Soft water contains Sodium (Na) ions which bond with the soap to make lather, in contrast to the hard water, it contains less Na ions therefore it should produce less lather. Based on this theory I predict that the more lather that appears in the test tube the softer the water should be.

Method

Apparatus:

  •  5 Test tubes
  •  2 Test tube racks
  • Beaker
  • Measuring cylinder
  • 5 Samples of water labelled A to E
  • Ruler accurate to 1mm
  • ...

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