Carol asks…
Predict which solvent will dissolve more of the given solute?
These are from one of my exams that I didn’t do so well in. Can you please explain this to me? I’m having a make-up test tomorrow. Thanks.
(a) Sodium chloride in methanol (CH3OH) or in propanol (CH3CH2CH2OH)
(b) Ethylene glycol (HOCH2CH2OH) in hexane (CH3CH2CH2CH2CH2CH3) or in water.
(c) Diethyl ether (CH3CH2OCH2CH3) in water or in ethanol (CH3CH2OH)
weight loss cardiff answers:
(a) Methanol – NaCl is ionic and will form ion-dipoles with the -OH groups of
both methanol and propanol. Propanol is less hydrophillic (water loving and
polar) to the dispersion forces to a greater extent.
(b) Water – Hexane has no dipoles and is non-polar. It will not interact with the
-OH groups in ethylene glycol. Water can H bond to the ethylene glycol.
(c) Ethanol – Diethyl ether can interact through a dipole and dispersion forces.
Ethanol can provide both while water would like to H bond.
Lisa asks…
Please help explain vapor pressure through the following calculation?
Diethyl ether has a DeltaH°vap of 29.1 kJ/mol and a vapor pressure of 0.703 atm at 25.0°C. What is its vapor pressure at 60.0°C?
final anwser should be in atm.
weight loss cardiff answers:
Clausius Clapyron equation:
ln(p1/p2) = (∆Hv/R) (1/T2 – 1/T1)
Just substitute (T in Kelvins)
ln(p1 / 0.703 atm) = [(29,100 J/mol) / (8.314472 J/K*mol)] (1/298 K – 1/333 K)
Solving, p1 = 2.42 atm.
The vapor pressure is above 1 atm 60.0 °C because the normal boiling point is 35 °C.
Mary asks…
You are busy carrying out an experiment when a classmate asks for your help.?
You are busy carrying out an experiment when a classmate asks for your help.
Your friend is holding up a reaction tube and seems confused about which layer is
aqueous and which is organic. You are in the middle of a different experiment
and you have no idea what is in the reaction tube. So you ask your friend about
the solvent he has used for his experiment. Your friend says he thinks he used
diethyl ether, but is not sure. He shows you the bottle from which he obtained the
solvent, but the label seems to be faded. What can you do to help your friend
solve the mystery about the aqueous and organic layers?
weight loss cardiff answers:
Mark the interface on the tube, add a little more solvent (or water) and see which layer gets bigger.
Works every time.
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