/15. Chem 202 Name KEY Exam 1 January 30, (3 pts total, 15 pts each) circle the best answer

Size: px

Start display at page:

Download "/15. Chem 202 Name KEY Exam 1 January 30, (3 pts total, 15 pts each) circle the best answer"

Fay Cunningham
5 years ago
Views:

1 Chem 202 KEY Exam 1 January 30, (3 pts total, 15 pts each) circle the best answer Which of the following is (are) true? a. Charles Law assume V and T are constant b. Boyles law assumes P and V are constant c. Avogadros hypothesis assumes T and P are constant e. none of the above. A real gas behaves ideally when a. P is high and T is low b. T is high and P is low c. the a and b constants in the van der Waals equation are both zero d. both a and c e. both b and c If a 1.0 liter sample of 1.00 mole of oxygen gas and another 1.0 liter sample of 2.00 moles of nitrogen gas are both at 25.0 o C, both gas samples: a. have molecules with the same average speed b. have molecules with the same average kinetic energy c. have the same pressure e. a and b only That I(l) has a higher boiling point than Br(l) is primarily due to I(l) having: a. a higher dipole moment b. a greater difference in electronegativity between the two atoms bonded c. a greater polarizability d. a greater charge e. all of the above Which of the following is true? a. Cl 2 has a higher boiling point than LiCl b. Cl has a higher boiling point than F c. e would be more soluble than Kr in a polar solvent e. none of the above /15

2 Chemistry 202, Exam 1, Page 2 2. (8 pts) Ethane (C 3 C 3 ) and ydrazine (N 2 N 2 ) have similar molecular weights, but very different boiling points. Draw the Lewis Dot Diagrams of these two molecules, indicate which is higher boiling, and explain why in one concise sentence: Lewis Dot Ethane: : C : C : Lewis Dot ydrazine: : N : N : igher boiling species = hydrazine because the lone electron pairs on nitrogen allow hydrogen bonding between N atoms on two hydrazine molecules. 3. (10 pts) Propane has the structural formula of C C C Both 1-propanol and ethyl methyl ether have the formula C 3 8 O, but they differ in their structural formula and in their viscosity. Draw the structural formulas of these two molecules, indicate which has the higher viscosity, and explain why in one concise sentence: Structural formula of 1-propanol: C C C O Structural formula of ethyl methyl ether: C C O C More viscous species = 1-propanol because hydrogen bonding can occur between hydroxyl groups in alcohol, but not with an ether, /18

3 Chemistry 202, Exam 1, Page 3 4. (14 pts) Assuming ideal behavior, what is the density (in grams per liter) of a sample of propane gas (C 3 8 ) at a pressure of 743 torr and 26.7 o C? " 1 atm % 743 torr$ ' n V = P RT = # 760 torr& = mole/liter lit atm mol K ( 300.0K) mole liter " g % $ ' = # 1 mole C38& g liter 5. (16 pts) Aluminum metal reacts with a strong acid as indicated: 2 Al(s) (aq) = 2 Al 3+ (aq) (g) Assume that g of aluminum metal are reacted with excess strong acid as shown above. The generated hydrogen gas is collected over water at a temperature of 30.0 o C at and a total gas volume of liters. The vapor pressure of water at this temperature is 31.8 torr. What will be the total pressure, in torrs, of the gas mixture collected? (Assume ideal gas behavior, that hydrogen is not soluble in water, and Dalton s law of partial pressure.) " 1 mole Al% " g Al $ ' 3 moles % 2 $ ' = moles # g &# 2 moles Al & 2 " lit atm% P 2 = n R T.2780 mol $ '( K) # mol K& = =.6915 atm V Liter " 760 torr% P total = P 2 + P 2O =.6915 atm$ ' torr = torr # 1 atm & /30

4 Chemistry 202, Exam 1, Page 4 6. (12 pts) An unknown pure substance is analyzed to contain 37.43% aluminum, 49.99% carbon, and 12.58% hydrogen by mass. Determine the empirical formula of this substance g Al (1 mol Al/ g) = mol Al divide by = g C (1 mol C/ g) = mol C divide by = g (1 mol/ g) = mol divide by = 9.00 Emp Formula = AlC 3 9 (EFW = g/mole) 7. (14 pts) The gaseous substance in the previous problem is analyzed by the Dumas method. A ml gas sample at o C and a pressure of 723 torr weighed g. Determine both the molecular weight and the molecular formula of the substance. MW = grt PV = " lit atm% g $ ' K # mol K& " 1 atm % 723 torr $ ' (.2525 Lit) # 760 torr& ( ) = g/mole 144.2/72.1 = 2; Formula = 2 x emp formula = Al 2 C 6 18 /26

5 Chemistry 202, Exam 1, Page 5 8. (11 points) Consider the diagram to the right. On it are indicated two points (A and B) and three regions (C, D, and E) P, (atm) 2.85 Region C Region D Region E Point A Point B T ( C) a. Identify the two points and the three regions indicated above: Point A is called the critical Point B is called the triple Region C is called the solid Region D is called the liquid Region E is called the gas Point Point b. If the current pressure is 2 Atm. and the current temperature is 250 C, what will happen as the pressure is increased to 45 Atm.? The initial gas will be compressed into a liquid. c. If the current pressure is 2 Atm. and the current temperature is 250 C, what will happen as the temperature is decreased to 0 C? The initial gas is cooled until it deposits and becomes a solid. /11

SUPeR Chemistry CH 222 Practice Exam

SUPeR Chemistry CH 222 Practice Exam This exam has been designed to help you practice working multiple choice problems over the material that will be covered on the first CH 222 midterm. The actual exams