Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

Science Class 10

Class 10 : Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

The document Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev is a part of the Class 10 Course Science Class 10.
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Our Objective
To study the comparative cleaning capacity of a sample of soap in soft and hard water.

The Theory
Ordinary water does not remove dirt from clothes or skin because the dirt present is oily or greasy in nature. Soaps are one of the most commonly used cleansing agents and are capable of reacting with water to remove  dirt. They are either animal origin or plant in origin.
Chemically, they are water soluble sodium or potassium salts of higher fatty acids such as stearic acid, palmitic acid or oleic acid. Fatty acids are found in fats and oils. When fat or oil is treated with alkali such as caustic soda or caustic potash soap and glycerin are produced.                          

Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

The soap molecule is generally represented as RCOONa. In solution, it ionizes to form RCOO- and Na+. Each soap molecule has a polar head group (carboxylate ion, COO- group) and a long non-polar hydrocarbon tail (R group from long chain fatty acid). The polar head attracts the polar water molecule and is called hydrophilic end and the non-polar tail attracts the water insoluble oily or greasy dirt particles.

When a dirty cloth is placed in soap solution, the long non-polar hydrocarbon tail of soap molecules points towards the oily dirt particles and the polar heads point towards the water. This forms a spherical structure with polar parts of the molecule on the surface and non-polar parts in the center. This spherical structure is called micelle. This micelle is attracted towards water and carries the oily dirt particles along with it. This causes the dirt particles to detach from the fibres of the cloth. In this manner, clothes become free from dirt or dust.

Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

Other important cleansing agents are synthetic detergents. These are sodium salts of long chain sulphonic acids and are generally represented as RSO3Na. The cleansing action of soaps and detergents are same.

Rubbing of clothes with brush or agitation in a washing machine loosens the bond between the dirt particles and the fibres of clothes. This supports the cleansing action of soaps and detergents.

Classification of Water

Water, along with soap, is used for washing purposes. On the basis of effective washing with soap, water has been classified as soft water and hard water.

Soft water: Water which produces good lather with soap is called soft water. When water falls as rain, it is naturally soft. Washing with soap is easy in soft water.

Hard water: Water which does not produce good lather with soap is called hard water. It is difficult to wash with soap in hard water. Water seeping through the ground becomes hard water. It is not useful for laundry and laboratory purposes.

Cleaning Capacity of Soap with Hard and Soft Water

Although soap is a good cleaning agent, its cleaning capacity is reduced when used in hard water. Hardness of water is due to the presence of sulphates, chlorides or bicarbonate salts of Ca2+ or Mg2+ ions. Soaps are sodium or potassium salts of long chain fatty acids. When soap is added to hard water, the Ca2+ and Mg2+ ions present in hard water react with soap. The sodium salts present in soaps are converted to their corresponding calcium and magnesium salts which are precipitated as scum. The insoluble scum sticks on the clothes and so the cleaning capacity of soap is reduced.
Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev
Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

The cleaning action of soap is very effective in soft water because it contains negligible calcium and magnesium ions.

Synthetic detergents are used in the case of hard water also because the calcium and magnesium salts of detergents are soluble in water. Detergents are more soluble than soaps and hence form more lather than soaps.

Types of Water Hardness: There are two types of water hardness.

  • Temporary hardness:It is a type of water hardness caused by the presence of dissolved bicarbonate salts of calcium or magnesium. Temporary hardness can be removed by boiling. When temporary hard water is boiled, the bicarbonates of calcium and magnesium undergo decomposition to form insoluble carbonates.
    Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev
    Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev
  • The insoluble carbonates of calcium and magnesium can be removed by filtration and the water thus obtained is free from calcium and magnesium ions and is soft.
  • Permanent hardness:This type of water hardness is due to the presence of calcium or magnesium sulphates or chlorides. Permanent hardness cannot be removed by boiling. It can be removed by using water softeners.
  • Cleaning with soap is effective in soft water. Soap lathers better in soft water and is scum free.   Things become cleaner and time, money and energy are saved.

Learning Outcomes

  • Students understand the terms: micelle, hard water, soft water, temporary hardness, and permanent hardness.
  • Students acquire knowledge of the cleaning capacity of soap in hard and soft water.
  • Based on the acquired skill, students will be able to classify the given water as hard water or soft water.
  • Students acquire skills to perform the experiment in the real lab.
Materials required:
  • Three beakers
  • Three test tubes
  • Distilled water
  • Well water
  • 2 g Calcium chloride
  • Three glass rods
  • Three pieces of soap each weighing 1 g 
  • Measuring cylinder 
  • Measuring scale  
  • Cloth pieces (5 cm x 5 cm )    
  • Ink     
  • Dropper

Real Lab Procedure:

  • Take three beakers and label them as A, B and C.
  • In beaker A, put 20ml of distilled water using a measuring cylinder.
  • In beaker B, put 20 ml of water obtained from a well using another measuring cylinder.
  • In beaker C, add 20 ml of distilled water. To this, add 2 g of calcium chloride and stir with a glass rod till it dissolves.
  • Take three soap pieces, each weighing 1g.
  • Add one soap piece to each beaker A, B and C.
  • Stir the contents in the beakers with separate glass rods to ensure that soap has dissolved.
  • In case the soap does not dissolve completely, heat the beaker gently on a Bunsen flame with constant stirring.
  • In beaker A, the soap solution formed is almost clear, in beaker B, some turbidity is observed and in beaker C scum is formed.
  • Take three test tubes and label them as A, B and C and place them in a test tube rack.
  • Pour 10 ml of soap solution from beaker A into test tube A and 10 ml of soap solution from beaker B into test tube B and 10 ml of soap solution from beaker C into test tube C, using separate measuring cylinders.
  • Measure the initial length of each soap solution with a measuring scale.
  • Hold the test tube A by hand.
  • Close its mouth with the thumb and shake it thoroughly 10 times in upward-downward direction.
  • It is observed that lather has formed in the test tube.
  • Measure the length of foam and the final length of the soap solution with the measuring scale.
  • Repeat the above four steps for test tubes B and C.

Simulator Procedure:

To start the experiment, select any one of the procedure  from ‘Select Procedure’ drop down list.

If the procedure selected is,

Distilled water

  • Drag the soap piece towards the beaker to add it into the beaker containing distilled water.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn on the burner by clicking on the ‘knob’ of the burner.
  • Drag the beaker towards the Bunsen burner to place it over the burner and gently heat it.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn off the burner by clicking on the ‘knob’ of the burner.
  • Click on the information to see the inference.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Click on the test tube to move it up.
  • Click on the beaker to pour soap solution into the test tube.
  • Click on the test tube to zoom it.
  • Drag the scale towards the test tube and measure the initial length of the soap solution.
  • Click on the close button to go to the previous stage.
  • Click on the test tube to shake it up and down.
  • Click on the information icon to see the inference.
  • Click on the test tube to zoom it. 
  • Drag the scale towards the test tube and measure the length of the lather and final length of the soap solution.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Drag the cloth piece containing ink spot towards the beaker to put it into the beaker containing soap solution.
  • Click on the beaker to see the zoomed view of cloth.
  • Click on the information icon to see the inference.
  • You can redo the experiment anytime by clicking on the ‘Reset’ button.
Well water
  • Drag the soap piece towards the beaker to add it into the beaker containing well water.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn on the burner by clicking on the ‘knob’ of the burner.
  • Drag the beaker towards the Bunsen burner to place it over the burner and gently heat it.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn off the burner by clicking on the ‘knob’ of the burner.
  • Click on the information to see the inference.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Click on the test tube to move it up.
  • Click on the beaker to pour soap solution into the test tube.
  • Click on the test tube to zoom it.
  • Drag the scale towards the test tube and measure the initial length of the soap solution.
  • Click on the close button to go to the previous stage.
  • Click on the test tube to shake it up and down.
  • Click on the information icon to see the inference.
  • Click on the test tube to zoom it. 
  • Drag the scale towards the test tube and measure the length of the lather and final length of the soap solution.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Drag the cloth piece containing ink spot towards the beaker to put it into the beaker containing soap solution.
  • Click on the beaker to see the zoomed view of cloth.
  • Click on the information icon to see the inference.
  • You can redo the experiment anytime by clicking on the ‘Reset’ button.
Distilled water + CaCl2 (s)
  • Drag the soap piece towards the beaker to add it into the beaker containing distilled water with dissolved calcium chloride.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn on the burner by clicking on the ‘knob’ of the burner.
  • Drag the beaker towards the Bunsen burner to place it over the burner and gently heat it.
  • Click on the glass rod to stir the mixture in the beaker.
  • Turn off the burner by clicking on the ‘knob’ of the burner.
  • Click on the information to see the inference.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Click on the test tube to move it up.
  • Click on the beaker to pour soap solution into the test tube.
  • Click on the test tube to zoom it.
  • Drag the scale towards the test tube and measure the initial length of the soap solution.
  • Click on the close button to go to the previous stage.
  • Click on the test tube to shake it up and down.
  • Click on the information icon to see the inference.
  • Click on the test tube to zoom it. 
  • Drag the scale towards the test tube and measure the length of the lather and final length of the soap solution.
  • Click on the ‘NEXT STEP’ button to go to the next process.
  • Drag the cloth piece containing ink spot towards the beaker to put it into the beaker containing soap solution.
  • Click on the beaker to see the zoomed view of cloth.
  • Click on the information icon to see the inference.
  • You can redo the experiment anytime by clicking on the ‘Reset’ button.

Observations:

Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

  • Take three pieces of white cloth of size 5 cm x 5 cm each.
  • Put a drop of ink in the centre of each cloth by means of a dropper and allow it to dry.
  • Place one piece of cloth with ink spot in the remaining soap solution in beaker A, another piece of cloth in beaker B and the third piece of cloth in beaker C.
  • Leave the three beakers undisturbed for about 10 min.
  • Remove the pieces of cloth from the beakers and rub each piece.
  • The ink spot on the cloth in soap solution A has almost disappeared
  • The ink spot on the soap cloth in soap solution B partially disappeared.
  • There is no change in the colour of the ink spot on the piece of cloth dipped in soap solution C, and some scum has been deposited on the surface of the cloth piece.

Conclusions:

Theory & Procedure, Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

Precautions:

  • Use the same sample and same weight of soap for the beakers A, B and C.
  • While stirring the soap solution, do not spill any solution out of the beaker.
  • In case the soap does not dissolve completely, heat the beaker gently with constant stirring on a Bunsen flame. Place the wire gauze on the tripod stand, to ensure heating is gentle and evaporation of water is avoided. Evaporation will reduce the volume of the water.
  • Carefully measure the same quantity of soap solution from the beakers A, B and C to put in the experimental test tubes A, B and C.
  • Give equal number of shakes to the test tubes A, B and C in the same way, without spilling any soap solution.
  • Immediately measure the length of foam produced.
  • The quantity of ink put on each piece of cloth should be equal.
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Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

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Cleaning Capacity of Soap with Hard and Soft Water Class 10 Notes | EduRev

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