How can we obtain pure potassium nitrate which is free of soil?
Potassium nitrate (saltpetre) is used as a fertilizer. It occurs naturally, mixed with soil, in many countries. Potassium nitrate is very soluble in hot water, but not very soluble in cold water.
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Potassium nitrate is very soluble in hot water but not in cold water. To obtain pure potassium nitrate from soil follow these steps:
- Take soil rich in potassium nitrate in a beaker.
- First pour cold water water into the beaker. All the chemicals that are soluble in cold water will get dissolved in the water when this is done.
- Strain the soil-water mixture through a fine filter to eliminate the water and collect the soil left behind.
- Now pour water into the soil collected in the previous step and heat it till the water starts to boil. When this is done the potassium nitrate from the soil gets dissolved in the water.
- Again strain the soil-water mixture while the water is hot.This time collect the water and discard the soil.
- Allow the water to cool. As the temperature of water cools the potassium nitrate will precipitate and can be collected.
There are numerous ways to obtain saltpeter from other salts, combined with nitric acid.
KOH + HNO3 -> KNO3 + H2O
2K + 2HNO3 -> 2KNO3 + H2
K2O + 2HNO3 -> 2KNO3 + H2O
2KOH + N2O5 -> 2KNO3 + H2O
NaNO3 + KCl -> KNO3 + NaCl
K2CO3 + 2HNO3 -> 2KNO3 + H2O + CO2
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