Assorted General Chemistry Problems
10.40) Many gases are shipped in high-pressure containers. Consider a steel tank whose volume is 65.0L and which contains O2 gas at a pressure of 16,500kPa at 23°C. a. What mass of O2 gas does the tank contain? b. What volume would the gas occupy at STP? c. At what temperature would the pressure in the tank equal 150.0atm? d. What would be the pressure of the gas, in kPa, if it were transferred to a container at 24°C whose volume is 55.0L?
10.97) Ammonia, NH3(g), and hydrogen chloride, HCl(g), react to form solid a ammonium chloride, NH4Cl(s):
NH3(g) + HCl(g)  NH4Cl(s)
Two 2.00-L flasks at 25°C are connected by a stopcock. One flask contains 5.00g NH3(g), and the other contains 5.00g HCl(g).
When the stopcock is opened, the gases react until one is completely consumed. a. Which gas will remain in the system after the reaction is complete? b. What will be the final pressure of the system after the reaction is complete? (Neglect the volume of the ammonium chloride formed.)
11.22) Propyl alcohol (CH3CH2CH2OH) and isopropyl alcohol [(CH3)2CHOH], whose space-filling models have boiling points of 97.2°C and 82.5°C, respectively. Explain why the boiling point of propyl alcohol is higher, even though both have the molecular formula of C3H8O.
11.40) The fluorocarbon composed C2Cl3F3 has a normal boiling point of 47.6°C. The specific heats of C2Cl3F3(l) and C2Cl3F3(g) are 0.91J/g-K and 0.67J/g-K, respectively. The heat of vaporization for the compound is 27.49kJ/mol. Calculate the heat required to convert 25.0g of C2Cl3F3 from a liquid at 5.00°C to a gas at 82.00°C.
11.60) Rutile is a mineral composed of Ti and O. Its unit cell contains Ti atoms at each corner and a Ti atom at the center of the cell. Four O atoms are on the opposite faces of the cell, and two are entirely within the cell. a. What is the chemical formula of this mineral? b. What is the nature of the bonding that holds the solid together?
11.78) For each of the following pairs of substances, predict which will have the higher melting point, and indicate why. a. HF, HCl; b. C (graphite), CH4; c. KBr, Br2; d. LiF, MgF2.
12.28) Write the structural formulas for the two substances that are condensed to form Kevlar ®.
12.38) Silicon carbide, SiC, is a three dimensional structure. Describe how the bonding and structure of SiC lead to its great thermal stability (to 2700°C) and exceptional hardness.
12.84) Although polyethylene can twist and turn in random ways the most stable form is a linear one with the carbon backbone. a. What is the hybridization of orbitals at each carbon atom? What angles do you expect between the bonds? b. Now imagine that the polymer is polypropylene rather than polyethylene. Draw structures for polypropylene in which (i) the CH3 groups all lie on the same side of the plane of the paper; (ii) the CH3 groups lie on alternating sides of the paper; or (iii) the CH3 groups are randomly distributed on either side. Which of these forms would you expect to have the highest crystallinity an melting point, and which the lowest? Explain in terms of intermolecular interactions and molecular shapes. c. Polypropylene fibers have been employed in athletic wear. The product is said to be superior to cotton or polyester clothing in wicking moisture away from the body through fabric to the outside. Explain the differenced between polypropylene and polyester or cotton, in terms of intermolecular interactions with water.
13.44) The density of toluene (C7H8) is 0.867g/mL, and the density of thiophene (C4H4S) is 1.065g/mL. A solution is made by dissolving 10.0g of thiophene in 250.0mL of toluene. a. Calculate the mole fraction of thiophene in the solution. b. Calculate the molality of thiophene in the solution. c. Assuming that the volumes of the solute and solvent are additive, what is the molarity of thiophene in the solution?
13. 72) Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00g of lauryl alcohol in 0.100kg of benzene freezes at 4.1°C. What is the approximate molar mass of lauryl alcohol?
13.90) Acetonitrile (CH3CN) is a polar organic solvent that dissolves a wide range of solutes, including many salts. The density of a 1.80 M LiBr solution in acetonitrile is 0.826g/cm3. Calculate the concentration of the solution in a. molality, b. mole fraction of LiBr, c. mass percentage of CH3CN. Solution Summary
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