40) Benzene has a melting point of 5.53 °C and a boiling point of 80.09 °C at at

Question

40) Benzene has a melting point of 5.53 °C and a boiling point of 80.09 °C at atmospheric pressure. Its density = 48.34 atm, and a triple point at T 5.52 °C, and P 0.0473 atm. Starting from a point at 200 K and 66.5 atm, trace the following path on a phase diagram: (1) First, increase T to 585 K while keeping P constant (2) Next, decrease P to 38.5 atm while keeping T constant. (3) Then, decrease T to 278.66 K while keeping P constant. (4) Finally, decrease P to 0.0025 atm while keeping T constant. What is your starting phase, and what is your final phase? (Hint: In order to answer the question, you may need to construct a phase diagram based on the given data.) 41) Calculate the amount of water (in grams) that must be added to (a) 5.00 g of urea (NH2) CO in the preparation of a 16.2 percent by mass solution, and (b) 26.2 g of MgCl in the preparation of a 15.0 percent by mass solution

Explanation / Answer

40. i am unable to upload the phase diagram but according to my diagram the starting phase of benzene was solid and final phase is gas.

starting point had temperature even les sthan the triple point(where solid, liquid and gas phases coexist) and pressure higher than critical pressure. hence, it was in solid state.

final point had temperature greater than triple point but pressure extremely less, lesser than triple point preussure. so it was in gas phase

41. percent by mass or mass percent means 1g solute in 100g total solution.

(a) you want 16.2% by mass, i.e, 16.2 g urea in 100g water

you have 5g urea

simple cross multiplication

(5*100)/16.2= 30.86g

you need to dissolve 5g urea in 30.86g water to get 16.2% by mass solution

(b) 15 g in 100g

26.2g in = (26.2*100)/15

=174.67g

mix 26.2g MgCl2 in 174.67g water to get 15% by mass solution

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