9) 13.2 mg of an unknown non-volatile compound is dissolved in 403 mL of water at 25C. If the solution has an osmotic pressure of 10.44 torr, what is the molar mass of the compound? Show work
A) 223 g/mol B) 68.3 g/mol C) 168 g/mol D) 58.3 g/mol E) 195 g/mol
Answer D)58.3 g/mole
= CRT
where
= osmotic pressure of solution, C= concentration of solution (mol/L) and T = temperature of solution in K
Supposw molar mass of given compound = x g/mole
Number of moles of compound = 0.0132 g/ x g/mole =(0.0132/x) moles
Molarity of the solution = Number of moles of solute / Volume of solution in L = (0.0132/x) moles/0.403 L = (0.032754/x) M
= osmotic pressure of solution = 10.44 torr = (10.44/760) atm
T = temperature of solution = (25 +273) = 298 K
Hence
(10.44/760) atm = (0.032754/x) M X 0.082 L.atm/mol.K X 298 K
x = 58.3
molar mass of given compound = 58.3 g/mole
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