Question

when 2.5g of non-volatile solute added into 75g of Water the vapour pressure of solutions is found to be 710mm of He. what be the molar mass of solute if vapour pressure of pure solvent is 700mm of Hg
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Answer 1

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Answer:

Molar mass of solute = 2.5 / 0.06 = 41.67

Explanation:

The formula that would be applied is;

(Pactual − Pnew)/ Pactual = nsolute / nsolvent

Here Pactual is the original vapor pressure, and P new is the vapor pressure after the solute is added to solvent. Also nsolute is the number of moles of solute and nsolvent is the number of moles of solvent

Now,

number of moles of water = 75 / 18 = 4.167

700 - 710 / 700 = nsolute / 4.167

nsolute = 0.06  

Molar mass of solute = 2.5 / 0.06 = 41.67

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