
Why do soaps not work in hard water?
Answer
521.4k+ views
Hint: Hard water has salts of the elements which belong to the s-block, especially group 2 elements. When the soap and the salts combine a precipitate is formed rather than mixing up.
Complete step by step answer:
Natural water contains dissolved salts. Depending on the behavior towards soap solution water is classified as soft and hard water:
Soft water: Water that produces lather with soap readily is called soft water. Examples of soft water are rainwater, distilled water, and demineralized water.
Hard water: Water that does not form lather easily with water is called hard water. Some examples of hard water are river water, seawater, spring water, etc.
Cause of hardness of water: It has been established that hardness of water is due to the presence of bicarbonates, chlorides, and sulphonates of magnesium and calcium in it. Hard water does not form lather easily with soap or soap does not work in hard water. This is because:
Soap is sodium or potassium salt of certain higher fatty acids such as stearic acid, palmitic acid, etc. When hard water is treated with soap solution, \[C{{a}^{2+}}\] and \[M{{g}^{2+}}\] ions present in hard water react with the anions of fatty acids present in soap to form scum or curdy white precipitates. As a result, hard water does not produce lather with soap immediately.
\[2{{C}_{17}}{{H}_{35}}CO{{O}^{-}}N{{a}^{+}}+CaC{{l}_{2}}\to {{({{C}_{17}}{{H}_{35}}COO)}_{2}}Ca\downarrow +2NaCl\]
\[2{{C}_{17}}{{H}_{35}}CO{{O}^{-}}N{{a}^{+}}+MgS{{O}_{4}}\to {{({{C}_{17}}{{H}_{35}}COO)}_{2}}Mg\downarrow +N{{a}_{2}}S{{O}_{4}}\]
Thus, hard water is not suitable for washing purposes since a lot of soap is wasted in precipitating out and ions present in hard water.
Note:
However, when all the \[C{{a}^{2+}}\] and \[M{{g}^{2+}}\] ions present in hard water have been precipitated by addition of sufficient amount of soap, resulting water becomes soft and readily produce lather with soap. Instead, we can use detergent in the hard water because it forms lather with detergent.
Complete step by step answer:
Natural water contains dissolved salts. Depending on the behavior towards soap solution water is classified as soft and hard water:
Soft water: Water that produces lather with soap readily is called soft water. Examples of soft water are rainwater, distilled water, and demineralized water.
Hard water: Water that does not form lather easily with water is called hard water. Some examples of hard water are river water, seawater, spring water, etc.
Cause of hardness of water: It has been established that hardness of water is due to the presence of bicarbonates, chlorides, and sulphonates of magnesium and calcium in it. Hard water does not form lather easily with soap or soap does not work in hard water. This is because:
Soap is sodium or potassium salt of certain higher fatty acids such as stearic acid, palmitic acid, etc. When hard water is treated with soap solution, \[C{{a}^{2+}}\] and \[M{{g}^{2+}}\] ions present in hard water react with the anions of fatty acids present in soap to form scum or curdy white precipitates. As a result, hard water does not produce lather with soap immediately.
\[2{{C}_{17}}{{H}_{35}}CO{{O}^{-}}N{{a}^{+}}+CaC{{l}_{2}}\to {{({{C}_{17}}{{H}_{35}}COO)}_{2}}Ca\downarrow +2NaCl\]
\[2{{C}_{17}}{{H}_{35}}CO{{O}^{-}}N{{a}^{+}}+MgS{{O}_{4}}\to {{({{C}_{17}}{{H}_{35}}COO)}_{2}}Mg\downarrow +N{{a}_{2}}S{{O}_{4}}\]
Thus, hard water is not suitable for washing purposes since a lot of soap is wasted in precipitating out and ions present in hard water.
Note:
However, when all the \[C{{a}^{2+}}\] and \[M{{g}^{2+}}\] ions present in hard water have been precipitated by addition of sufficient amount of soap, resulting water becomes soft and readily produce lather with soap. Instead, we can use detergent in the hard water because it forms lather with detergent.
Recently Updated Pages
Master Class 11 Accountancy: Engaging Questions & Answers for Success

Master Class 11 Science: Engaging Questions & Answers for Success

While covering a distance of 30km Ajeet takes 2 ho-class-11-maths-CBSE

Sanjeevani booti brought about by Lord Hanuman to cure class 11 biology CBSE

A police jeep on patrol duty on a national highway class 11 physics CBSE

Master Class 12 Economics: Engaging Questions & Answers for Success

Trending doubts
Which one is a true fish A Jellyfish B Starfish C Dogfish class 10 biology CBSE

The Equation xxx + 2 is Satisfied when x is Equal to Class 10 Maths

Why is there a time difference of about 5 hours between class 10 social science CBSE

Fill the blanks with proper collective nouns 1 A of class 10 english CBSE

Write examples of herbivores carnivores and omnivo class 10 biology CBSE

When and how did Canada eventually gain its independence class 10 social science CBSE
