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Solutions — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistrySolutions5 Marks
Question
Concentration terms such as mass percentage, ppm, mole fraction and molality are independent of temperature, however molarity is a function of temperature. Explain.
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Answer

Molarity of a solution is a weight by volume relationship to represent its strength and defined as 'The number of moles of solute dissolved in one litre of solution'. Since volume depends on temperature and undergoes a change with change in temperature, the molarity will also change with change in temperature. On the other hand, the other concentration terms such as mass percentage, ppm, mole fraction and molality are based upon mass by mass relationship of solute and solvent present in a binary solution. Mass does not change with change in temperature, as a result these concentration terms remain unchanged wth variation of temperature. According to the definition of all these terms, mass of the solvent used for making the solution is related to the mass of solute.

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