{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Exam 1-solutions

# Exam 1-solutions - Version 026 – Exam 1 – fakhreddine...

This preview shows pages 1–3. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Version 026 – Exam 1 – fakhreddine – (51615) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Kb for benzene is 2.53 C/m and Kf for ben- zene is 5.12 C/m The freezing point of a benzene solution is 2 ◦ C. What is the expected normal boiling point of the solution? The normal freezing point of benzene is 5 . 5 ◦ C and the normal boiling point of benzene is 80 . 1 ◦ C. 1. 83.24 ◦ C 2. 81.83 ◦ C correct 3. 80.20 ◦ C 4. None of these 5. 78.06 ◦ C 6. 79.32 ◦ C Explanation: T 1 = 2 ◦ C k f = 5 . 12 K · mol / kg T 2 = 5 . 5 ◦ C k b = 5 . 12 K · mol / kg Δ T f = 5 . 5 ◦ C- 2 ◦ C = 3 . 5 K = k f m m = Δ T f k f = 3 . 5 K 5 . 12 K · mol / kg = 0 . 683594 mol / kg . The change in boiling point temperature is Δ T b = k b m = 2 . 53 K · mol / kg (0 . 683594 mol / kg) = 1 . 72949 K = 1 . 72949 ◦ C . and the boiling point is BP = 80 . 1 ◦ C + 1 . 72949 ◦ C = 81 . 8295 ◦ C . 002 10.0 points Which one of the following statements is false? 1. Carbon tetrachloride (CCl 4 ) is more mis- cible with hexane (C 6 H 14 ) than it is with a polar solvent such as methanol (CH 3 OH). 2. Gases are generally more soluble in water at high temperatures than at low tempera- tures. correct 3. As temperature increases, the solubilities of some solids in liquids increase and the sol- ubilities of other solids in liquids decrease. 4. Gases are generally more soluble in water under high pressures than under low pres- sures. 5. Water dissolves many ionic solutes be- cause of its ability to hydrate ions in solu- tion. Explanation: The polarity of water allows it to hydrate the individual ions in the ionic solute. CCl 4 is non-polar and will be miscible with another non-polar liquid and not with a polar one. Increasing temperature makes salts with exothermic Δ H sol more soluble, but salts with endothermic Δ H sol less soluble. Gases are generally more soluble in water under high pressures than under low pressures because of Henry’s Law; as the pressure of a gas above a liquid increases, the concentration of the gas in the solution increases. 003 10.0 points Calculate the temperature at which pure wa- ter would boil at a pressure of 404 torr. The heat of vaporization of water is 40431 J / mol at 100 ◦ C. 1. 85.011 2. 89.1842 3. 75.1136 4. 74.1965 5. 82.7572 Version 026 – Exam 1 – fakhreddine – (51615) 2 6. 81.2316 7. 90.9374 8. 76.9366 9. 86.6584 10. 75.9019 Correct answer: 82 . 7572 ◦ C. Explanation: P 1 =760 torr P 2 = 404 torr T 1 = 100 ◦ C + 273 = 373 K T 2 = ? Δ H = 40431 J / mol ln P 2 P 1 = Δ H R parenleftbigg 1 T 1- 1 T 2 parenrightbigg R Δ H ln P 2 P 1 = 1 T 1- 1 T 2 1 T 2 = 1 T 1- R Δ H ln parenleftbigg P 2 P 1 parenrightbigg = 1 373 K- bracketleftbigg 8 . 314 J / mol · K 41000 J / mol × ln parenleftbigg 404 torr 760 torr parenrightbiggbracketrightbigg = 0 . 00281091 K − 1 T 2 = 355 . 757 K- 273 = 82...
View Full Document

{[ snackBarMessage ]}

### Page1 / 9

Exam 1-solutions - Version 026 – Exam 1 – fakhreddine...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online