Cleaning Capacity of any Soap in Hard and Soft Water

This article will help you to discern the procedure of dirt extraction from clothes with the help of soap. This information presented in this article is solely dedicated to the students who want to perform practical science experiments along with learning the functionality of soap in soft and hard water. This will help in determining the properties of ethanoic acid, acetic acid, the odor, reaction with sodium bicarbonate, solubility in water, and effect on litmus paper.

The Objective of the Experiment

With this experiment, students will be able to learn about the comparative cleaning capacity of soap in soft and hard water. 

Materials Required for the Experiment

  1. Test tube stand

  2. Two test tubes

  3. A measuring cylinder

The Theory

In the study of comparative cleaning capacity of soap in soft and hard water, H2O, in its normal form, sometimes fails to remove dirt and grime from the clothes even after several washes. This is because the dirt or stain present on the clothes has oil content or has a greasy nature. Soaps are one of the commonly used cleaning agents that are used for removing all types of stains and dirt. It reacts with water to extract the oil content and make the cloth clean. Soaps are either formed from animals or plants. They contain potassium salts of water-soluble sodium with higher fatty acids like palmitic acids, stearic acids, or oleic acids. Most fatty acids are available in oils and fats. When oil or fat is mixed alkali like caustic potash soap or caustic soda and glycerin, the cleaning abilities are developed.

Determining Soft Water

Soft water is free from harsh minerals that tend to damage our body and things on which it has been used. Soft water is gentle for our home and body. Soft water does not have much content like calcium and magnesium and, thus, helps in the prevention of scale buildup around the house, including pipelines and appliances. Soft water helps in increasing the effectiveness of soap when compared to hard water. Hard water has a higher chance of inactivating the cleaning quality of soap's ingredients. In terms of health, soft water helps in treating dryness and preventing stickiness caused by cool weather, hard water, and low humidity. Soft water ensures silkier & softer skin and hair after every wash. 

Determining Hard Water

Hard water is water that is rich in magnesium and calcium contents. These are two naturally available minerals in the water. These two minerals are essential for health but not appreciable in terms of general water usage. Hardness in water can cause damage to your home. While using hard water for daily works, you can notice a film of residue on the dishes, or the formation of spots in shower or clothes. Sometimes it is possible to discover fine particles inside the appliances, especially when it comes to dishwasher or laundry machines. Heating hard water can leave deposits of calcium in the beaker. A daily accumulation of calcium deposits can damage the lifespan and performance of any appliance. To make it worse, the heating expenses will skyrocket, and the appliance's efficiencies will certainly plunge. Hardness in water also causes ill effects on personal hygiene. It may give you a feel of residual hair and skin after washing. This makes our skin and hair more dry and brittle.

Getting on with the Experiment

Procedure 1:

  1. Take two plastic cups

  2. Label them with "A" and "B."

  3. Pour soft or distilled water in the cup labeled "A."

  4. Pour a solution of water and plaster of Paris (calcium sulfate) in the cup labeled with "B."

  5. This will help in creating your own hard water. The CaSO4 may not entirely mix with water, but that's okay. 

  6. Add some drops of liquid soap in both the cups

  7. Take a straw and gently blow air into both the liquids.

  8. Observe and record the results


Plastic Cups



Forms good amount of lather


Forms a lesser amount lather when compared to "A." 


  • After this experiment, you can clearly differentiate the qualities and properties of soft and hard water.

  • The cup marked with the letter "B" requires more blowing of air to match the quantity of lather produced by the other counterpart. 

  • Soft water clearly suds more successfully. 

Things to Keep in Mind

  1. Add sufficient and same amount of liquid soap to both the cups so that the differences can be determined based on equal conditions. 

  2. Take cups with the same height, breath, and diameter.

  3. Mix the soap in the similar pattern.

  4. Make sure to blow the same amount and speed of air in both the cups.

Procedure 2:

This experiment will help in determining the quality of water you have in your home

  1. Take a bottle and mark it with the letter "X."

  2. Fill 1/3 of it with tap water 

  3. Mix some liquid soap to the water and shake vigorously for some time. Make sure to use a basic soap that is free from perfumes, dyes, and detergents.

  4. Take a bottle and mark it with the letter "Y."

  5. Fill 1/3 of it with distilled water.

  6. Follow the same step as mentioned in 3


Plastic cups



Lacks in the formation of fluffy bubbles and the appearance may become milky or cloudy


Will form lots of bubbles, sometimes clearing out the resting part of the water left at the bottom of the bottle "X." 


  • After this experiment, you can clearly determine the quality and probable damage you are facing from the daily usage of hard water.

  • The bottle marked with the letter "X" will near the appearance of "Y" only if you receive soft or lesser hard water from home taps. Remember, no tap water can match the quality or richness of bubbles formed from the bottle "Y." 

Things to keep in mind

  1. Add equal and ample amounts of liquid soap to both the bottles so that the experiment clearly indicates the quality of water. 

  2. Take the equal size of the bottles.

  3. Mix the soap gently in both the bottles.

How to Remove Hardness from Water?

Temporary hardness can be removed by boiling the water. It is caused by the presence of dissolved bicarbonate salts of magnesium or calcium. The process of boiling helps in decomposing calcium and magnesium to form insoluble carbonates.

Ca(HCO₃)₂ (aq) [Calcium Bicarbonate] ---Boil---> CaCO₃ (s) [Calcium Carbonate] + CO₂ (g) [Carbon dioxide] + H₂O [Water]

Mg(HCO₃)₂ (aq) [Magnesium Bicarbonate] ---Boil---> MgCO₃ (s) [Magnesium Carbonate] + CO₂

(g) [Carbon dioxide] + H₂O [Water]

The insoluble carbonates of magnesium and calcium can be removed through proper filtration and the result leaves you with water that is free from calcium and magnesium ions. 

FAQ (Frequently Asked Questions)

Q.1. Define the Cleaning Capacity of Soap in Hard Water

Ans. The cleaning capacity of soap in hard water diminishes a lot when compared to soft water. This is caused due to the presence of calcium and magnesium contents in the water. High water is rich in these minerals and, thus, causes damage to appliances and other household products.

Q.2. What Happens When We Mix Soap with Hard Water?

Ans. When soap is mixed with hard water, the ions of Ca2+ and Mg2+, which are already present in the water, causes a reaction. Soaps contain sodium salts, and thus, the reaction converts them into their corresponding calcium and magnesium salts. This generates precipitation and is seen as scum. The scum becomes insoluble and, therefore, sticks with the cloths to reduce the cleaning capacity of soap.

Q.3. Why Soap is Ineffective When Mixed with Acidic Water?

Ans. Soaps are formed from the salts of weak acids, which is why they are vulnerable to acidic water. The salts in the soap get converted into free fatty acids due to the presence of mineral acids. These fatty acids are not much soluble when compared with potassium or sodium salts. This leads to the formation of precipitation or soap scum. This indicates that soaps are ineffective in acidic water.

Q.4. How to Keep Clothes White Even after Washing in Hard Water?

Ans. If staying away from hard water isn't possible, consider opting for a couple of alternatives to increase the brightness of whites. Wash white clothes with regular detergents with a mixture of half cup hydrogen peroxide or a large tablespoon of borax powder. You can also purchase some products that help in keeping out the iron contents.

Q.5. Is Rainfall Hard or Soft?

Ans. Rainwater is naturally soft, but when it makes its way through the ground to the waterways, it becomes prone to hardness due to the exposure of lime, chalk, magnesium, and calcium. Hard water is good for drinking but not for daily works.

Q.6. How to Soften Hard Water?

Ans. Hard water can be softened by bringing it to the boiling point. You can also opt for a filter with an RO system that helps in the removal of ions and other unwanted molecules from water.