Hard water is any water containing an appreciable quantity of dissolved minerals.
Some of the minerals come from chalk, limestone or marble, which the water may have flowed over or through. Hard water contains calcium or magnesium ions. Limestone, marble or chalks are insoluble in pure water however they will dissolve slowly in acidic rain. If your water has emerged through limestone or chalk (calcium carbonate) it will be hard. Soft water is gratification water in which the only cation (positively charged ion) is sodium.The minerals in water give it an idiosyncratic taste.
Some natural mineral waters are highly desired for their flavour and the health benefits they may converse. Extremely hard water affects plumbing such as pipes and the performance of certain cleaning agents. When the water is heated the carbonates precipitate out of solution, forming scale in pipes and kettles. Calcium Hydrogen Carbonate and Magnesium Hydrogen Carbonate decompose when they are heated.
The original insoluble carbonate is reformed. This happens when water is boiled.Calcium Hydrogen Carbonate + Carbon Dioxide + Water + Calcium Carbonate. Ca(HCO3)2(aq)+CO2(g) + H2O(l) + CaCO3(s).
Magnesium Hydrogen Carbonate + Carbon Dioxide + Water + Magnesium Carbonate. Mg(HCO3)2(aq) CO2(g) + H2O(l) + MgCO3(s).Boiling the water causes the precipitation of solid calcium carbonate or solid magnesium carbonate. This removes the calcium ions or magnesium ions from the water and so removes the hardness.
Therefore, hardness due to Hydrogen Carbonates is said to be temporary. Calcium sulphate is slightly soluble in water when a river flows over Gypsum; it dissolves some of the rock. Therefore calcium gets into the water. How hard and soft water react with soap.The cardinal disadvantage of hard water is that the dissolved ions (calcium and magnesium) react with the chemicals in soap to create a white precipitate. This effect occurs because the 2 +ions destroy the surfactant properties of the soap by forming a solid precipitate.
Majority of soaps are made from compounds of sodium and potassium for example, sodium stearate. Sodium stearate chemically reacts with calcium compounds in the water to produce calcium stearate. Sodium stearate dissolves in water, but calcium stearate doesn't, meaning you get less lather (it doesn’t bind together). Hard water is often indicated by a lack of suds formation when soap is disconcerted in water, and by the accumulation of lime scale.With hard water, soap solutions form a white precipitate instead of producing lather. Soap is more effective in soft water because it has little or no calcium or magnesium therefore it produces a relatively good lather because no calcium or magnesium salts are being made (soap scum).
Where hard water is most likely to be found in the UK and the reasons why In the Lake District and most areas of Scotland, the water is soft because it is mainly drawn out of surface water and the contact time between water and earth is short. Furthermore, there is not much chalk in the soil to be dissolved. Wales, Devon, Cornwall and parts of North-West England are softer water areas, and range from 0 to 200 ppm this is because they have fresh and pure valleys and streams that don’t come in to contact or have little contact with chalk, limestone or marble. Generally water is mostly hard in urban areas of England where soft water sources are unavailable.
Certain parts of London have hard water because there is a lot of chalk and much of the water is pumped from underground where there has been a longer contact time, hence, the water is hard.Alternative methods for testing the hardness of water other than using soap solution Hardness is most commonly measured by titration with an EDTA solution. A titration involves adding small amounts of a solution to a water sample until the sample changes colour. EDTA is a chelating agent that can donate electrons therefore forming a complex with metal ions. You can titrate a sample for total hardness using a burette or hard water test kit.
You can also measure calcium hardness separately from magnesium hardness by adjusting the pH and using different indicators.Another experiment for testing the hardness of water is Test strips. Using a hard water test strip, a colour develops on the strip and the strip is matched to a chart. The degree of colour change from light yellow to dark red is proportional to the amount of hardness.
The chart shows colours for concentrations; with dark red being above 180 ppm (very hard water). This is a quick and easy test for a rough estimate of water hardness.The colourmetric method consists of using a chemical called calgamite which binds together with calcium and magnesium ions. This then produces a red colouration in the water to signify the hardness of the water.
The colormetric device shines a LED light through the water to measure the intensity of the colour change (red light). The light reddens depending on the amount of ions. A reading over 180 ppm means the water is considered to be very hard.
