AP Chemistry - Raoult's Law 1. What specific fact about a physical property of a solution must be true to call it a colligative property? 2. What specific property must be present for Raoult's Law to be true? 3. What causes a solution with a nonvolatile solute to have  a lower vapor pressure than the pure solvent at the same temperature? 4. How is Raoult's Law used when we want to calculate the total vapor pressure of a liquid solution made up of two volatile liquids? 5. What kinds of data would have to be obtained to find out if a binary solution of two miscible liquids is almost exactly an ideal solution? 6. The vapor pressure of water at 20oC is 2.33 kPa.  A 20% w/w solution of ethylene glycol in water is prepared.  Assuming that the solute is non-volatile, do a calculation to estimate the vapor pressure of the solution. 7. Pentane and heptane are two hydrocarbon liquids present in gasoline.  At 20oC, the vapor pressure of pentane is 56.00 kPa and the vapor pressure of heptane is4.80 kPa.  What is the total vapor pressure of a solution prepared with a concentration of 30.0 mole percent pentane in heptane? 8. Benzene and toluene help give lead-free good engine performance.  At 40oC, the vapor pressure of benzene is 24.0 kPa, and that of toluene is 8.0 kPa.  To prepare a solution of these that have at 40oC a total vapor pressure of 12.8 kPa requires what mole percent concentration of each? 9. At 21.0oC, a solution of 19.35 grams of a non-volatile, non-polar compound in 34.88 g of ethyl bromide, C2H5Br, had a vapor pressure of 44.80 kPa.  The vapor pressure of pure ethyl bromide at this temperature is 53.33 kPa.  Calculate the following: a)  The mole fractions of solute and solvent b)  The moles of solute present c)  The formula weight of the solute 10. At 20oC, the vapor pressure of cyclohexane, a hydrocarbon solvent, is 8.92 kPa and that of toluene (another solvent) is 2.81 kPa.   What is the vapor pressure of a solution of these two at 20oC when each is present at a mole fraction of 0.500?