A Tale of Vinegar and Hard Water
If you live in an area where the water is hard, you may notice
that when you wash utensils, a thin white stain is left behind. Did you know you
can use vinegar to remove these stains?
Sometimes, the water that you get from wells looks a little cloudy and tastes odd. This is called hard water, because it has many insoluble salts mixed in it. Water without such salts is called soft water.
Water in the ground has many ions dissolved in it, including sodium, calcium and magnesium. When the water comes to the surface, it dissolves some carbon dioxide from the air. The carbon dioxide reacts with the dissolved ions to form their respective carbonates. While sodium carbonate dissolves readily in water, calcium and magnesium carbonates do not. They remain present in the water as a fine suspension. You find hard water mostly in coastal and limestone-rich areas.
Where soft water is rare, people use it for bathing and cooking purposes. Hard water is used for the rest. The salts from the hard water adhere to the surface of the utensils, form a fine deposit. This cannot be washed away using soap, because it is insoluble in water. Over time, the deposit accumulates, and makes the vessel unsightly. It must then be cleaned with vinegar.
Vinegar contains acetic acid, which is chemically a ‘stronger’ acid than carbonic acid. In principle, the anion of a stronger acid will displace the anion of a weaker acid from a salt. Therefore, acetic acid reacts with calcium carbonate to form calcium acetate and the carbonic acid, both of which are soluble in water, and get washed away.
To clean a utensil, rinse it in vinegar and leave it for some time to let the acetic acid act. Then wash with a lot of water, and your deposit will have vanished!
What is hard water?
Sometimes, the water that you get from wells looks a little cloudy and tastes odd. This is called hard water, because it has many insoluble salts mixed in it. Water without such salts is called soft water.
Water in the ground has many ions dissolved in it, including sodium, calcium and magnesium. When the water comes to the surface, it dissolves some carbon dioxide from the air. The carbon dioxide reacts with the dissolved ions to form their respective carbonates. While sodium carbonate dissolves readily in water, calcium and magnesium carbonates do not. They remain present in the water as a fine suspension. You find hard water mostly in coastal and limestone-rich areas.
Insoluble deposits
Where soft water is rare, people use it for bathing and cooking purposes. Hard water is used for the rest. The salts from the hard water adhere to the surface of the utensils, form a fine deposit. This cannot be washed away using soap, because it is insoluble in water. Over time, the deposit accumulates, and makes the vessel unsightly. It must then be cleaned with vinegar.
Vinegar and the strength of acids
Vinegar contains acetic acid, which is chemically a ‘stronger’ acid than carbonic acid. In principle, the anion of a stronger acid will displace the anion of a weaker acid from a salt. Therefore, acetic acid reacts with calcium carbonate to form calcium acetate and the carbonic acid, both of which are soluble in water, and get washed away.
To clean a utensil, rinse it in vinegar and leave it for some time to let the acetic acid act. Then wash with a lot of water, and your deposit will have vanished!
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