Hardness of Water: Temporary and Permanent Hardness in Water

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The reason water feels hard is because of the dissolved bicarbonates, chlorides, and sulfates of calcium and magnesium. If water doesn’t create a lather with soap, it’s considered hard water.

Water stands as the most vital substance crucial for sustaining life on Earth. It exists in oceans, rivers, ponds, lakes, glaciers, and more. Rainwater is regarded as pure since it lacks dissolved salts, despite having some dissolved gases.

Water can be categorized into two types: hard water and soft water.

  • Soft water: This type easily forms a lather with soap and is typically rainwater. It is ideal for household chores like laundry and cleaning.
  • Hard water: Named for the presence of calcium and magnesium salts, hard water doesn’t lather with soap but instead creates a precipitate.

What Is Hard Water?

Hard water contains a significant amount of minerals. It develops when water seeps through deposits of chalk and limestone, composed mainly of magnesium and calcium carbonates. As hard water doesn’t create lather with soap, it’s unsuitable for laundry purposes.

Read More: Calcium Carbonate, Formula, Properties, Uses, Application

The hardness of water poses a threat to boilers due to the buildup of salts, causing a decline in boiler efficiency. While hard water is safe for drinking, prolonged use can result in various issues such as:

  • Skin Irritations: The skin may experience strains or discomfort.
  • Increased Water Appliance Strain: Water appliances may operate more strenuously, leading to higher water bills.
  • Stains on Fabrics: Clothes and linens may develop noticeable spots.

Types of Hardness of Water

The hardness of water can be classified into two types:

  • Temporary Hardness 
  • Permanent Hardness

Temporary Hardness of Water

  • Water becomes temporarily hard due to the presence of magnesium and calcium carbonates. Boiling the water can help eliminate this hardness.
  • During boiling, the soluble salts like Mg(HCO3)2 transform into Mg(OH)2, forming an insoluble precipitate that can be removed. After filtration, the resulting water is considered soft water.

Permanent Hardness of Water

  • If the water contains soluble salts of magnesium and calcium in the form of chlorides and sulfides, it is termed permanent hardness because boiling alone cannot eliminate this hardness.
  • To address permanent hardness, we can use washing soda. When washing soda reacts with the sulfide and chloride salts of magnesium and calcium, it forms insoluble carbonates. This chemical reaction converts hard water into soft water.

Drawbacks of Hard Water

  • Excessive Soap Usage: Hard water leads to the wastage of soap as it does not lather easily.
  • Increased Fuel Consumption: The use of hard water often results in higher fuel consumption.
  • Scale Formation on Metal Boilers: Metallic boilers may accumulate scales due to the hardness of water, affecting their efficiency over time.

Remove the Hardness of Water (Temporarily)

Boiling Method

  • Boiling causes soluble bicarbonates to transform into insoluble carbonates, which can then be easily removed through filtration.

Reactions:

  • Ca(HCO3)2 → ΔCaCO3↓ + H2O + CO2
  • Mg(HCO3)2 → ΔMgCO3↓ + H2O + CO2

Clark’s Method

  • Calcium hydroxide, known as Clark’s reagent, is employed. It works by converting bicarbonates into carbonates, thus removing water hardness.

Reaction

  • Ca(OH)2 + Ca(HCO3)2 → 2CaCO3↓ + 2H2O

Read More: Calcium Hydroxide: Physical and Chemical Properties and Uses

Removing Permanent Hardness of Water

Gan’s Permutit Method

  • Utilizes sodium aluminium ortho silicate, also known as permutit or zeolite, to eliminate permanent water hardness.

Reaction

  • Na2 Al2 Si2 O8.KH2O + Ca++ → 2Na+ + Ca Al2 Si2 O8.xH2O

Calgon’s Process

  • Involves sodium-hexa-meta-phosphate (NaPO3)6, commonly called Calgon. The hardness in water is eliminated through the adsorption of Ca++ and Mg++ ions.

Ion Exchange Resin Method

  • This method utilizes resins to remove permanent water hardness. Ca++/Mg++ ions are exchanged with Cl, and SO4-2 ions are exchanged with anion exchange resin (RNH2OH). This results in the formation of demineralized water.

Reactions

  • 2RCOOH + Ca++ → (RCOO)2Ca + 2H+
  • RNH2OH + Cl → RNH2Cl + OH
  • H+ + OH → H2O

Harmful Effects of Hard Water

Several prevalent indications of hard water include:

  • Dull and Rough Textures: Fabrics, linens, and clothes may lose their brightness and feel coarse.
  • Stains and Scale Build-Up: Unsightly stains on white porcelain and the accumulation of scale on faucets.
  • Reduced Shower Pressure: Showers may experience lower water pressure due to pipe blockages.
  • White Residue on Dishes: Chalky, white deposits or spots can appear on dishes.
  • Shower Stains: Stains may develop in the shower, indicating the presence of hard water.

Frequently Asked Questions

Q1. What is water hardness?

Water hardness is a measure of the mineral content, primarily calcium and magnesium, present in water. It is typically categorized as temporary or permanent.

Q2. How does hard water affect laundry?

Hard water can lead to dull and rough textures in clothes and linens due to the reduced effectiveness of soap in forming lather.

Q3. What is the difference between temporary and permanent hardness?

Temporary hardness is caused by the presence of bicarbonates of calcium and magnesium, which can be removed by boiling. Permanent hardness is due to chlorides and sulfides and requires different methods for removal.

Q4. How can we remove temporary hardness?

Boiling is a common method to remove temporary hardness. It involves converting soluble bicarbonates into insoluble carbonates, which can be filtered out.

Q5. What is Calgon, and how does it work in water treatment?

Calgon, or sodium hexa-metaphosphate, is used in water treatment to eliminate hardness by adsorbing calcium and magnesium ions.

Q6. How does ion exchange resin work in water softening?

Ion exchange resin replaces calcium and magnesium ions with chloride ions, effectively reducing water hardness.

Q7. What are the disadvantages of hard water?

Some drawbacks include increased soap usage, higher fuel consumption, and the formation of scales on metal boilers.

Q8. Can hard water affect skin health?

Hard water may lead to skin irritations and discomfort due to reduced lathering of soap.

Q9. How does water hardness impact household appliances?

Hard water can cause scale build-up in appliances like kettles and reduce their efficiency over time.

Q10. Are there any health concerns associated with hard water?

While hard water is generally safe to drink, prolonged use may lead to certain issues, and it’s advisable to address its impact on appliances and daily activities.

More Important Questions on Chemistry:


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As a professional blogger and passionate educator, I am driven by a deep-seated desire to share knowledge and empower others. With years of experience in the field, I am committed to providing valuable insights and guidance to aspiring learners. My passion lies in helping individuals discover their potential and achieve their goals. I am also a firm believer in the power of motivation and strive to inspire others to pursue their dreams with unwavering determination.

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