Version 063 – hw02 – Holcombe – (53570) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points At 75 ◦ , the vapor pressure of water, methanol, diethylether and benzene are 289, 1126, 2680, and 644 torr, respectively. Which of these is NOT above its boiling point at normal atmo- spheric pressure? 1. methanol, diethylether, and benzene 2. diethylether 3. None of these 4. water 5. methanol and diethylether 6. water and benzene correct Explanation: The vapor pressures for water and benzene are still below 760 torr at 75 ◦ C, which means that they are not up to the boiling point yet and are in fact, below the boiling point. Methanol and diethylether are well above 760 torr at this temperature which means they are above their normal boiling points. 002 10.0 points What is the vapor pressure of carbon disulfide at its normal boiling point? 1. 0.5 atm 2. 2.0 atm 3. 2.5 atm 4. 1.2 atm 5. 0.3 atm 6. 1.0 atm correct Explanation: 003 10.0 points The solubility of a gas such as O 2 in water (decreases, increases, stays the same) with increasing temperature. 1. increases 2. stays the same 3. decreases correct Explanation: At higher temperatures the gas molecules have more energy and are better able to es- cape from the solvent. 004 10.0 points According to Henry’s Law, the concentration of gas dissolved in water has what relationship to the pressure of the gas? 1. proportional to correct 2. inversely proportional to 3. independent of 4. exponentially dependent on Explanation: P = k X The amount of gas that dissolves increases as gas pressure increases. 005 10.0 points Which of the following is a FALSE state- ment? 1. The solubility of a gas decreases with in- creasing temperature. 2. The solubility of a gas depends both on temperature and pressure. 3. The solubility of a gas decreases with in- creasing pressure of a gas above the solution. correct 4. The solubility of a gas increases with in- creasing pressure of the gas above the solu-
Version 063 – hw02 – Holcombe – (53570) 2 tion. Explanation: Gases become more soluble as pressures increases and temperatures decrease. 006 10.0 points The solubility of oxygen at a certain tempera- ture is 8 ppm. If the partial pressure of oxygen is doubled at this temperature, the solubility is 16 ppm. 1. False 2. True correct Explanation: 007 10.0 points Hint: The units for Henry’s constant should indicate what form of Henry’s Law to use. Calculate the number of moles of oxygen that will dissolve in 45 L of water at 20 ◦ C if the partial pressure of oxygen is 0.21 atm. Henry’s constant for oxygen is 0.0013 mol L · atm . 1. 0.28 mol 2. 0.0062 mol 3. 0.0013 mol 4. 0.012 mol correct 5. 0.00027 mol Explanation: 008 10.0 points What is the vapor pressure of the solvent in an aqueous solution of glucose at 80 ◦ C if the mole fraction of glucose is 0 . 19? The vapor pressure of water at 80 ◦ C is 355 . 26 Torr.
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- Spring '09
- Chemistry, Vapor pressure, Torr, Torr Ptotal