10 States of Matter. Aubrey High School AP Chemistry. Period Date / / 10.2 Problems - Liquids and Gases

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1 Aubrey High School AP Chemistry 10 States of Matter 1. Use the following table to answer these questions. Vapor Pressures of Various Liquids Temp. ( C) Ethyl alcohol Benzene Methyl salicylate Water Carbon tetrachloride a. A beaker of benzene (C 6 H 6 ) is at room temperature (20 C). What is its vapor pressure? mmhg Is this vapor pressure large enough to cause the benzene to boil at sea level? b. When all of the liquids are heated to 80 C, which will boil when the air pressure is 760 mmhg? Name Period Date / / 10.2 Problems - Liquids and Gases d. A beaker of ethyl alcohol and a beaker of benzene both at room temperature (20 C) are placed on a hot plate when the air pressure is only 700 mmhg. Which one of the two liquids will start to boil first? It will boil at about what temperature? e. A beaker of carbon tetrachloride is warmed to 60 C and connected to a vacuum pump so the air pressure above the liquid can be changed. The pump is turned on. At what pressure will the liquid start to boil? mmhg What would this pressure be in atmospheres? atm [show work here] f. At 75 C, in a place where the air pressure is only 650 mmhg, which substances will be boiling? g. The pressure above the five substances is adjusted to 550 mmhg. What is the approximate boiling point of each substance at this pressure? [methyl salicylate is excluded] ethyl alcohol: water: benzene: carbon tetrachloride: h. At 550 mmhg, when the temperature is hot enough to get the ethyl alcohol to boil, will the carbon tetrachloride also be boiling? i. At 75 C, I start the pressure above the liquids at 760 mmhg and slowly reduce it using the vacuum pump. In which order will the substances boil? 1st 2nd 3rd 4th 5th c. If the temperature remains unchanged, but the pressure above the liquids is reduced to 700 mmhg which liquids will now boil?

2 j. Determine the approximate normal boiling point (boiling point at 760 mmhg) of each substance below: ethyl alcohol: water: benzene: carbon tetrachloride: k. Study the chart of vapor pressures at 25 C. Rank the substances in order of increasing IMFs. l. Why doesn t data for methyl salicylate start until 60 C? 2. The following graph shows vapor pressure curves for two substances, A and B: e. At what temperature is the vapor pressure of B equal to kpa? f. What is the normal boiling point of A? g. What is the normal boiling point of B? h. At what temperature would A boil if atmospheric pressure were 93.3 kpa? i. What would the atmospheric pressure have to be in order for B to boil at the temperature you gave as your answer to part h? 3. An ideal gas occupies a volume of 10 L at 27 C. If the pressure on the gas is tripled at this temperature, the volume changes. To what value must the temperature change to restore the volume to the initial 10 L at the new pressure? 4. Consider nitrogen gas. a. Calculate the root mean square speed of nitrogen gas at 25 C. b. What happens to the rms speed if the temperature is doubled to 50 C? a. What is the vapor pressure of A at 35 C? b. What is the vapor pressure of B at 35 C? c. At what temperature is the vapor pressure of A equal to kpa? d. What is the vapor pressure of B at this temperature? c. For nitrogen, the van der Waals constants a and b have values of 1.39 and respectively. Calculate the pressure of 5 moles of nitrogen gas confined to a 1.0 L vessel at a temperature of 300 K using the ideal gas equation and the van der Waals equation of state. Comment on the difference.

3 5. If 1.0 L of oxygen at 2.0 atm pressure, 2.00 L of nitrogen at 1.0 atm pressure, and 2.0 L of helium at 2.0 atm pressure, are all mixed in a 3.0 L vessel with no change in temperature, what is the final pressure of the mixture in the 3.0 L vessel? 6. A gas diffuses 5/3 times faster than carbon dioxide. Which gas might it be? a. O 2 b. N 2 c. CO d. He e. CH 4 7. What is the density of the helium gas at 0.34 atm and 33 C? 8. If the density of a gas is 1.2 g/l at 745 torr and 20. C, what is its molar mass? AP Chemistry 1988 #8 The normal boiling and freezing points of argon are 87.3 K and 84.0 K, respectively. The triple point is at 82.7 K and 0.68 atmosphere. (a) Use the data above to draw a phase diagram for argon. Label the axes and label the regions in which the solid, liquid, and gas phases are stable. On the phase diagram, show the position of the normal boiling point. (b) Describe any changes that can be observed in a sample of solid argon when the temperature is increases from 40 K to 160 K at a constant pressure of 0.50 atmosphere. (c) Describe any changes that can be observed in a sample of liquid argon the pressure is reduced from 10 atmospheres to 1 atmosphere at a constant temperature of 100 K, which is well below the critical temperature. (d) Does the liquid phase of argon have a density greater than, equal to, or less than the density of the solid phase? Explain your answer, using information given in the introduction to this question.

4 AP Chemistry 2011B #6 Use principles of molecular structure, intermolecular forces, and kinetic molecular theory to answer the following questions. (a) A complete Lewis electron-dot diagram of a molecule of ethyl methanoate is given below. (i) Identify the hybridization of the valence electrons of the carbon atom labeled C w. (ii) Estimate the numerical value of the H y C x O bond angle in an ethyl methanoate molecule. Explain the basis of your estimate. (b) Ethyl methanoate, CH 3CH 2OCHO, is synthesized in the laboratory from ethanol, C 2H 5OH, and methanoic acid, HCOOH, as represented by the following equation. C 2H 5OH(l) + HCOOH(l) CH 3CH 2OCHO(l) + H 2O(l) (i) In the box below, draw the complete Lewis electron-dot diagram of a methanoic acid molecule. Methanoic Acid (ii) In the box below, draw the complete Lewis electron-dot diagrams of a methanoic acid molecule and a water molecule in an orientation that allows a hydrogen bond to form between them. Hydrogen Bonding Between Methanoic Acid and Water (c) A small amount of liquid ethyl methanoate (boiling point 54 C) was placed in a rigid closed 2.0 L container containing argon gas at an initial pressure of 1.00 atm and a temperature of 20 C. The pressure in the container was monitored for 70. seconds after the ethyl methanoate was added, and the data in the graph below were obtained. It was observed that some liquid ethyl methanoate remained in the flask after 70. seconds. (Assume that the volume of the remaining liquid is negligible compared to the total volume of the container.) (i) Explain why the pressure in the flask increased during the first 60. seconds. (ii) Explain, in terms of processes occurring at the molecular level, why the pressure in the flask remained constant after 60. seconds.

6 (iii) What is the value of the partial pressure of ethyl methanoate vapor in the container at 60. seconds? (iv) After 80. seconds, additional liquid ethyl methanoate is added to the container at 20 C. Does the partial pressure of the ethyl methanoate vapor in the container increase, decrease, or stay the same? Explain. (Assume that the volume of the additional liquid ethyl methanoate in the container is negligible compared to the total volume of the container.) AP Chemistry 2004B #2 Answer the following questions related to hydrocarbons. (a) Determine the empirical formula of a hydrocarbon that contains 85.7 percent carbon by mass. (b) The density of the hydrocarbon in part (a) is 2.0 g L 1 at 50 C and atm. i. Calculate the molar mass of the hydrocarbon. ii. Determine the molecular formula of the hydrocarbon. (c) Two flasks are connected by a stopcock as shown below. The 5.0 L flask contains CH 4 at a pressure of 3.0 atm, and the 1.0 L flask contains C 2H 6 at a pressure of 0.55 atm. Calculate the total pressure of the system after the stopcock is opened. Assume that the temperature remains constant. (d) Octane, C 8H 18 (l), has a density of g ml 1 at 20 C. A 255 ml sample of C 8H 18 (l) measured at 20 C reacts completely with excess oxygen as represented by the equation below. 2 C 8H 18 (l) + 25 O 2 (g) 16 CO 2 (g) + 18 H 2O (g) Calculate the total number of moles of gaseous products formed.

10. 2 P R O B L E M S L I Q U I D S A N D G A S E S

10. 2 P R O B L E M S L I Q U I D S A N D G A S E S South Pasadena AP Chemistry Name 10 States of Matter Period Date 10. 2 P R B L E M S L I Q U I D S A N D G A S E S 1. Use the following table to answer these questions. Vapor Pressures of Various Liquids