Why doesnt hard water produce a lather with soap?
Hard water contains ions such as those of magnesium, Mg2+ and calcium, Ca2+. Soap contains the sodium (or potassium) salts of complex carboxylic acids, e.g. sodium stearate. Although the sodium (or potassium) salts of these acids are soluble in water, the corresponding salts of magnesium and calcium are insoluble. When soap comes into contact with hard water, a precipitation reaction occurs, and these insoluble salts are produced as a ‘scum’. The soap is therefore prevented from forming a lather and from carrying out its washing functions until all the magnesium and calcium ions have been removed by this precipitation process. Igloo Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely
