Rukia Rajper lecture for chemistry students.pptx

Chemistry student lecture

1. Hardness of water : The property of water to form an insoluble curd with soap instead of lather . In other words it is the soap destroying property due to the presence of bicarbonates , sulphates and chlorides of calcium and magnesium, Hard water . Doesn’t form a lather with soap

2. Water hardness primarily comes from dissolved calcium and magnesium ions, which are picked up as water flows through and over earth’s crust. These minerals, found in rocks like limestone and chalk, dissolve into the water, increasing its mineral content and causing hardness. Other minerals like iron, aluminum, and strontium can also contribute, though in smaller amounts.

3. Types of hardness of water: There are tow types of hardness 1) Temporary hardness 2) permeant hardness 1) Temporary hardness : Temporary Hardness (Carbonate Hardness):
Cause: Dissolved bicarbonates of calcium and magnesium.
Removal: Boiling the water, which causes the bicarbonates to precipitate out as carbonates.
Example: Calcium bicarbonate (Ca(HCO3)2) decomposes to calcium carbonate (CaCO3), which is insoluble and can be filtered out.

4. Permeant hardness of water Permanent Hardness (Non-Carbonate Hardness):
Cause: Dissolved sulfates and chlorides of calcium and magnesium.
Removal: Requires chemical treatment methods like ion exchange, lime softening, chelation, or reverse osmosis.
Examples: Calcium sulfate (CaSO4), magnesium chloride (MgCl2).

5. How to removed permeant hardness: Permanent hardness of water, caused by dissolved calcium and magnesium salts like chlorides and sulphates , can be removed by chemical methods such as adding washing soda (sodium carbonate) or a complexinG agent like sodium hexametaphosphate ( Calgon ), or by physical methods like the ion-exchange (zeolite) process or reverse osmosis, which effectively removes the hardness-causing ions.

6. Chemical methods Washing Soda (Sodium Carbonate, Na2co3)
Process: Adding sodium carbonate ( Na₂.co ₃) to the water forms insoluble calcium and magnesium carbonates, which then precipitate out and can be removed by filtration.
Reaction: The carbonate ions from the washing soda react with the dissolved calcium and magnesium ions, effectively removing them from the water as solid precipitates.

7. 2)Reverse osmosis : A Reverse osmosis (RO) water filter is a system that uses a semi-permeable membrane to remove a wide spectrum of contaminants from drinking water. The multi-stage process applies pressure to force tap water through filters, leaving contaminants behind and producing highly purified water .

8. Ion exchange Method ( water softener: The resin beads have a high affinity for the dissolved calcium (Ca2+) and magnesium (Mg2+) ions that cause water hardness.
As water passes over the resin, the hardness ions are attracted to and held by the resin.
In exchange, the resin releases an equal number of less objectionable ions, typically sodium (Na+) in water softeners, into the water.
This exchange effectively replaces the hard-water causing ions with soft-water causing ions .

9. Benefits of hard water Researchers have also found that drinking hard water has been associated with a decrease in cardiovascular disease-related mortality. Magnesium helps regulate your cardiac muscles, while calcium keeps the sodium-potassium balance in your cardiac muscles in check, which they need to function.

10. Type of hardness : s