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Why does the solubility of Glauber's salt first increase upto 32.4 C and then decrease ?

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The solubility first increases up to 32.4 0C, then decreases. This is due to  Sodium sulphate is a decahydrate complex i.e., has 10 water molecules for every molecule of sodium sulphate. At the above said temperature, the crystal breaks into a sulphate liquid phase and an anhydrous solid phase. That is why after that temperature the solubility decreases as it depends on the anhydrous sulphate. 

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Ans. Due to the fact that this salt is found as a hydrated salt (first Na2SO4.10H20 and then as Na2SO4.7H2O, so, with the increase of temperature it looses moisture (water)). When the Na2SO4.10H2O is heated the solution of this compound decreases because a solid phase and a liquid phase are formed after the initial heating.
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Ans. The solubility actually increased up to 32.4 degrees Celsius, then declines. This is explain by the following:
Sodium sulfate is naturally found as a decahydrate complex (has 10 water molecules in the crystal for every molecule of sodium sulfate). At 32.4 degress Celsium, the crystal breaks into a sulfate liquid phase and and an anydrous solid phase, or in other words, the extra molecules in the complex detach from the sodium sulfate part of the salt.
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