A solution has relative lowering of vapour pressure \(0.02\). If the total number of moles in the solution is \(5.0\), how many moles of solute are present?
Answer and explanation
Correct answer: \(0.10\,\mathrm{mol}\)
For an ideal solution containing a non-volatile solute, Raoult’s law gives the relative lowering of vapour pressure as the solute mole fraction: \(\Delta p/p^0=X_{\text{solute}}\). Thus, \(X_{\text{solute}}=0.02\). Since mole fraction equals solute moles divided by total moles, \(n_{\text{solute}}=0.02\times5.0=0.10\,\mathrm{mol}\). Therefore, option C is correct.
Frequently asked questions
What is the correct answer to this question?
\(0.10\,\mathrm{mol}\)
Why is this the correct answer?
For an ideal solution containing a non-volatile solute, Raoult’s law gives the relative lowering of vapour pressure as the solute mole fraction: \(\Delta p/p^0=X_{\text{solute}}\). Thus, \(X_{\text{solute}}=0.02\). Since mole fraction equals solute moles divided by total moles, \(n_{\text{solute}}=0.02\times5.0=0.10\,\mathrm{mol}\). Therefore, option C is correct.
Which subject and chapter does this question cover?
This is a Class 12 Chemistry question. Chapter: Chapter 01: Solutions. Topic: 4: Vapour Pressure.
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