To study the comparative cleaning capacity of a sample of soap in soft and hard water
Beakers, test tubes, 10 mL measuring cylinder, glass rod, marker.
Distilled water, calcium chloride, magnesium sulphate, soap, tap water, ground water, calcium chloride, magnesium sulphate.
Soap is sodium or potassium salt of higher fatty acid. Salts of higher fatty acids of metals other than sodium and potassium are insoluble in water generally and do not act as cleansing agent. In hard water soluble magnesium and calcium salts are present. These react with soap to form magnesium and calcium salts of fatty acids.
2C17H35COONa + MgSO4 -> (C17H35Coo)2 Mg (Insoluble) + Na2SO4
2C17H35COONa + CaCl2 -> (C17H35Coo)2 Ca (Insoluble) + 2NaCl
Hence, soap reacts with salts of hard water which decreases cleansing capacity of soap in hard water.
(1) Four clean beakers are marked as A, B, C and D.
(2) 20 mL each of distilled water, ground water, distilled water and distilled water are taken in A, B, C and D beakers, respectively.
(3) 0.5 g CaC12 and 0.5 g MgSO4 are added to C and D beakers, respectively.
(4) In each beaker pieces of 1-1 g soap are added.
(5) Content of all beakers are shaken to dissolve soap by clean glass rod.
(6) 3 mL solutions from each A, B, C and D beakers are taken and poured into A, B, C and D marked clean test tubes, respectively.
(7) A, B, C and D test tubes are shaken for equal times to produce lather and length of lather formed in test tubes are measured.
(1) Maximum and minimum length of lather formed is in A and D test tubes, respectively.
(2) Cleaning capacity of distilled water is maximum due to maximum lather formation.
(3) Water containing MgSO4 has minimum cleaning capacity due to minimum lather formation.
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