soalan past year PSPM II PDT phase +ve / -ve deviation

August 01

The boiling point of H₂O is 100°C while the boiling point of HNO₃ is 86°C. When these two solutions were added, the vapour pressure of the mixture was less than the vapour pressure of pure H₂O and pure HNO_3. The azeotropic mixture was formed when the per cent composition of HNO₃ is 68%.

State the type of deviation exhibited by the mixture. Explain

Sketch and label the diagrams of temperature-composition and vapour pressure-composition for the mixture.

State the product and residue for the distillation of a mixture containing 50% H₂O and 50% HNO₃.

August 02

A solution was formed by adding carbon tetrachloride to ethanol. The interacting

forces between molecules ethanol and between carbon tetrachloride molecules

were found to be greater than the interacting forces between ethanol and carbon

tetrachloride molecules.

i.      The solution deviates from Raoult’s law. Explain.

ii.     There was a change in temperature while forming the solution. Explain.

iii.     State whether the value of DH is positive or negative?

Sept 03

X and Y form an azeotropic mixture with composition of 42% X. The mixture boils at a temperature of 341 K and pressure of 760 torr. At this pressure, X and Y boil at 351 K and 353 K respectively.

Sketch the phase diagram of temperature versus per cent composition for the mixture.

Do these mixtures show positive or negative deviation from ideality? Explain.      State the distillate collected and the residue left in the flask if a mixture of 60% X and 40% Y is fractionally distillated.

Oct 05

The boiling point of an azeotropic mixture containing B and C with a mole 

 fraction x_B = 0.7 is 120°C. Pure B and C boil at 65°C and 90°C respectively. 

Sketch a labelled phase diagram from the above data.

Show in the diagram above the composition variation during successive boilings 

and condensations of a mixture with initial mole fraction, x_C=0.8.

A mixture with initial mole fraction, x_B=0.5 is distilled using fractional  distillation. Name the distillate and residue.

Oct 08

A mixture consisting of 0.40 mol fraction of hexane, C₆H₁₄, and 0.60 mol fraction of heptane, C₇H₁₆, forms an ideal solution. State two properties of an ideal solution and explain why a mixture of heptane-hexane forms an ideal solution.

 By drawing an appropriate phase diagram, state how the mixture of these liquids can be separated.

    

                [boiling point: C₆H₁₄ = 69^oC, C₇H₁₆ = 98^oC]