AP Chem-1st Semester Review

(cotton ball and tube) The experimental apparatus represented above is used to demonstrate the rates at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse from each end and meet somewhere in between, where they react to form a white solid. Which of the following combinations will produce a solid closest to the center of the tube? a. HCl and CH3NH2 b. HCl and NH3 c. HBr and CH3NH2 d. HBr and NH3

a

Are the most difficult to oxidize in a given period of the periodic table a. noble gases b. alkali metals c. halogens d. transition elements e. actinides

a

(3 boxes added make a larger one) The figure above represents three sealed 1.0 L vessels, each containing a different inert gas at 298 K. The pressure of Ar in the first vessel is 2.0 atm. The ratio of the numbers of Ar, Ne, and He atoms in the vessels is 2:1:6, respectively. After all the gases are combined in a previously evacuated 2.0 L vessel, what is the total pressure of the gases at 298 K? a. 3.0 atm b. 4.5 atm c. 9.0 atm d. 18 atm

b

(Inter and intra molecular forces b/w HF molecules) The figure above shows that in solid hydrogen fluoride there are two different distances between H atoms and F atoms. Which of the following best accounts for the two different distances? a. Accommodation of the necessary bond angles in the formation of the solid b. difference in strength between covalent bonds and intermolecular attractions c. different isotopes of fluorine present in the samples d. uneven repulsions among nonbonding electron pairs

b

(bar graph) The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. All of the following statements are true. Which one should be the best basis for concluding that the sample was pure Te? a. Te forms ions with a -2 charge whereas I forms ions with a -1 charge b. Te is more abundant than I in the universe c. I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope d. I has a higher first ionization energy than Te does

c

(molecular diagrams and table) Nonane and 2,3,4-trifluoropentane have almost identical molar masses, but nonae has a significantly higher boiling point. Which of the following statements best helps explain this observation? a. The C-F bond is easier to break than the C-H bond b. The C-F bond is more polar than the C-H bond c. The carbon chains are longer in nonane than they are in 2,3,4-trifluoropentane d. The carbon chains are farther apart in a sample of nonane than they are in 2,3,4-trifluoropentane

c

Are the most likely to form anions a. noble gases b. alkali metals c. halogens d. transition elements e. actinides

c

Cl2(g) + 2e- --> 2Cl-(g) Which of the following expression is equivalent to ^H* for the reaction represented above? a. x + y b. x - y c. x + 2y d. x/2 - y

c

Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the molecular formula of the compound? a. C2H2 b. C2H6 c. C4H8 d. C6H6

c

Container A B C Gas Methane Ethane Butane Temp 27 27 27 Molar mass 16 30 58 Pressure 2.0 4.0 2.0 If the pressure of each gas is increased at constant temperature until condensation occurs, which gas will condense at the lowest pressure? a. methane b. ethane c. butane d. all the gases will condense at the same pressure

c

Process ^H* K(l) --> K(g) v K(g) --> K+(g) + e- w Cl2(g) --> 2Cl(g) x Cl(g) +e- -->Cl-(g) y K+(g) + Cl-(g) --> KCl (s) z What remains in the reaction vessel after equal masses of K(s) and Cl2(g) have reacted until either one or both of the reactants have been completely consumed? a. KCl only b. KCl and K only c. KCl and Cl2 only d. KCl, K, and Cl2

c

(2 beakers added form one large beaker) Beaker X and beaker Y each contain 1.0 L of solution, as shown above. A student combines the solutions by pouring them into a larger, previously empty beaker Z and observes the formation of a white precipitate. Assuming that volumes are additive, which of the following sets of solutions could be represented by the diagram above? Beaker X Beaker Y Beaker Z a. 2.0 M AgNO3 2.0 M MgCl2 4.0 M Mg(NO3)2 and AgCl(s) b. 2.0 M AgNO3 2.0 M MgCl2 2.0 M Mg(NO3)2 and AgCl(s) c. 2.0 M AgNO3 1.0 M MgCl2 1.0 M Mg(NO3)2 and AgCl(s) d. 2.0 M AgNO3 1.0 M MgCl2 0.5 M Mg(NO3)2 and AgCl(s)

d

(2 lewis dot diagrams) Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are a. the same because the molecular formulas are similar b. the same because C and S have similar electronegativity values c. different because the lone pair of electrons on the S atom make it the negative end of a dipole d. different because S has a greater number of electron domains (regions of electron density) surrounding it then C has

d

Container A B C Gas Methane Ethane Butane Temp 27 27 27 Molar mass 16 30 58 Pressure 2.0 4.0 2.0 The average kinetic energy of the gas molecules is a. greatest in container A b. greatest in container B c. greatest in container C d. the same in all three containers

d

Consider a molecule with the formula CH2O2. The structure of this molecule has a geometry around the carbon atom similar to the geometry around carbon in methanamide. In the box provided below, draw the complete Lewis electron-dot diagram for the molecule.

:O: II .. H - C - O - H ''

As the vessel cools to room temperature, droplets of liquid water form on the inside walls of the container. Predict whether the pH of the water in the vessel is less than 7, equal to 7, or greater than 7. Explain your prediction.

Less than 7 because CO2 is soluble in water

An oxidation-reduction reaction that is also a synthesis reaction a. 2Mg(s) + )2(g) --> 2MgO(s) b. Pb2+(aq) + CrO42-(aq) --> PbCrO4(s) c. SO3(g) + 2H2)(l) --> H3O+(aq) + HSO4-(aq) d. 2H2O(g) --> 2H2(g) + O2(g) e. Ag+(aq) + 2NH3 (aq) --> [Ag(NH3)2]+(aq)

a

Ion Ionic radius (pm) Zn2+--74 Ca2+--100 Ba2+--135 Based on the data in the table above, which of the following correctly predicts the relative strength of the attraction of Zn2+, Ca2+, and Ba2+ ions to water molecules in a solution, from strongest to weakest, and provides the correct reason? a. Zn2+>Ca2+>Ba2+ because the smaller ions have a stronger coulombic attraction to water b. Zn2+>Ca2+>Ba2+ because the smaller ions are more electronegative c. Ba2+>Ca2+>Zn2+ because the larger ions are more polarizable d. Ba2+>Ca2+>Zn2+ because the larger ions are less electronegative

a

NaF MgO Boiling Point 1695 3600 Na+ Mg2+ F- Cl- O2- Ionic Radius 76 72 133 181 140 Based on the data in the table above, which of the following statements provides the best prediction for the boiling point of NaCl? a. NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF b. NaCl will have a boiling point between that of NaF and MgO because the covalent character of the bonds in NaCl is intermediate between that of MgO and NaF c. NaCl will have a higher boiling point than MgO because the ions are spaced farther apart in NaCl d. NaCl will have a higher boiling point than MgO because the energy required to transfer electrons from the anion to the cation is larger in NaCl than in MgO

a

Process ^H* K(l) --> K(g) v K(g) --> K+(g) + e- w Cl2(g) --> 2Cl(g) x Cl(g) +e- -->Cl-(g) y K+(g) + Cl-(g) --> KCl (s) z It is observed that the reaction producing KCl from its elements goes essentially to completion. Which fo the following is a true statement about the thermodynamic favorability of the reaction? a. The reaction is favorable and driven by an enthalpy change b. The reaction is unfavorable and driven by an entropy change only c. The reaction is favorable and driven by both enthalpy and entropy changes d. The reaction is unfavorable due to both enthalpy and entropy changes

a

Silicon crystals are semiconductors. Which of the following is a correct reason for the increase in the conductivity of Si crystals when a small fraction of Si atoms are replaced with those of a different element? a. P atoms introduce additional mobile negative charges b. P atoms introduce additional mobile positive charges c. Ge atoms have more electrons than Si atoms d. Ge atoms are much smaller than Si atoms

a

The mass percent of carbon in pure glucose, C6H12O6, is 40.0 percent. A chemist analyzes an impure sample of glucose and determines that the mass percent of carbon is 38.2 percent. Which of the following impurities could account for the low mass percent of carbon in the sample? a. water, h20 b. ribose, c5h10o5 c. fructose, c6h12o6, an isomer of glucose d. sucrose, c12h22o11

a

A 100 g sample of a metal was heated to 100*C and then quickly transferred to an insulated container holding 100 g of water at 22*C. The temperature of the water rose to reach a final temperature of 35*C. Which of the following can be concluded? a. The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained b. The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained c. The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water d. The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased

b

A precipitation reaction a. 2Mg(s) + )2(g) --> 2MgO(s) b. Pb2+(aq) + CrO42-(aq) --> PbCrO4(s) c. SO3(g) + 2H2)(l) --> H3O+(aq) + HSO4-(aq) d. 2H2O(g) --> 2H2(g) + O2(g) e. Ag+(aq) + 2NH3 (aq) --> [Ag(NH3)2]+(aq)

b

Atomic Radius 1st Ionization Energy Calcium 194 pm 590 kJ/mol Potassium --- --- Based on periodic trends and the data in the table above, which of the following are the most probable values of the atomic radius and the first ionization energy for potassium, respectively? a. 242 pm, 633 kJ/mol b. 242 pm, 419 kJ/mol c. 120 pm, 633 kJ/mol d. 120 pm, 419 kJ/mol

b

Container A B C Gas Methane Ethane Butane Temp 27 27 27 Molar mass 16 30 58 Pressure 2.0 4.0 2.0 The density of the gas, in g/L, is a. greatest in container A b. greatest in container B c. greatest in container C d. the same in all three containers

b

Process ^H* K(l) --> K(g) v K(g) --> K+(g) + e- w Cl2(g) --> 2Cl(g) x Cl(g) +e- -->Cl-(g) y K+(g) + Cl-(g) --> KCl (s) z Which of the values of ^H* for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)? a. z only b. y and z only c. x, y, and z only d. w, x, y, and z

b

(2 marshmallow-looking diagrams I2 is larger than Br2) The diagram above shows molecules of Br2 and I2 drawn to the same scale. Which of the following is the best explanation for the difference in the boiling points of liquid Br2 and I2, which are 59*C and 184*C, respectively? a. Solid iodine is a network covalent solid, whereas solid bromine is a molecular solid b. The covalent bonds in I2 molecules are weaker than those in Br2 molecules c. I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2 d. Bromine has a greater electronegativity than iodine, thus there are stronger dipole-dipole forces in liquid bromine than in liquid iodine

c

N2 molecules absorb ultraviolet light but not visible light. I2 molecules absorb both visible and ultraviolet light. Which of the following statements explains the observations? a. more energy is required to make N2 molecules vibrate than is required to make I2 molecules vibrate b. More energy is required to remove an electron form an I2 molecule than is required to remove an electron from a N2 molecule c. Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule d. The molecular mass of I2 is greater than the molecular mass of N2

c

Radius Melting Pt. Oxidation State Au 144 1064 1+, 3+ Cu 128 1085 1+, 2+ Ag 144 961 1+ To make Au stronger and harder, it is often alloyed with other metals, such as Cu and Ag. Consider two alloys, one of Au and Cu and one of Au and Ag, each with the same mole fraction of Au. If the Au/Cu alloy is harder than the Au/Ag alloy, then which of the following is the best explanation based on the information in the table above? a. Cu has two common oxidation states, but Ag has only one b. Cu has a higher melting point than Au has, but Ag has a lower melting point than Au has c. Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy d. Cu atoms are less polarizable than are Au or Ag atoms, thus Cu has weaker interparticle forces

c

Substance Equilibrium Vapor Pressure at 20*C C6H6-------75 torr C2H5OH--44 torr CH3OH--92 torr C2H6O2--0.06 torr Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces? a. C6H6 b. C2H5OH c. CH3OH d. C2H6O2

c

(Step 1: small block breaks apart Step 2: large block breaks apart Step 3: small pieces fit into the larger piece) The dissolution of an ionic solute in a polar solvent can be imaged as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, ^H, for each step? a. all three steps are exothermic b. all three steps are endothermic c. steps 1 and 2 are exothermic, and the final step is endothermic d. steps 1 and 2 are endothermic, and the final step is exothermic

d

(photoelectric spectra) The photoelectric spectra above show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum? a. Nitrogen atoms have a half-filled p subshell b. There are more electron-electron repulsions in oxygen atoms than in nitrogen atoms c. Electrons in the p subshell of oxygen atoms provide more shielding than electrons in the p subshell of nitrogen atoms d. Nitrogen atoms have a smaller nuclear charge than oxygen atoms

d

A Lewis acid-base reaction that produces a coordination complex a. 2Mg(s) + )2(g) --> 2MgO(s) b. Pb2+(aq) + CrO42-(aq) --> PbCrO4(s) c. SO3(g) + 2H2)(l) --> H3O+(aq) + HSO4-(aq) d. 2H2O(g) --> 2H2(g) + O2(g) e. Ag+(aq) + 2NH3 (aq) --> [Ag(NH3)2]+(aq)

e

i) Explain why ^H* for the formation of I2(g) from I2(s) is larger than ^H* for the formation of Br2(g) from Br2(l). In your explanation identify the type of particle interactions involved and a reason for the difference in magnitude of those interactions. ii) I2(s) and Br2(l) can react to form the compound IBr(l). Predict which would have the greater molar enthalpy of vaporization. IBr(l) or Br2(l). Justify your prediction.

i) Both have same bonds (covalent), but I2 is stronger because it's larger and has more electrons ii) IBr is polar and dipole-dipole forces tend to increase enthalpy

i) Explain why the hexane layer is light purple while the water layer is virtually colorless. Your explanation should reference the relative strengths of interactions between molecules of I2 and the solvents H2O and C6H14 and the reasons for the differences. ii) In which layer, water or hexane, would the concentration of I3- be higher? Explain

i) It's easier for hexane to dissolve in I2 because of london dispersion forces and H2O has strong hydrogen bonds ii) more soluble in water because like dissolves like

i) Identify a specific error in procedure made by the student that will result in a calculated value for the enthalpy of reaction that is higher than the accepted value ii) Explain how the error that you identified leads to a calculated value for the enthalpy of reaction that is higher than the accepted value

i) Read the thermometer incorrectly ii) If temp is too high, the calculated molar enthalpy is too high

i) Using the data in the table below, calculate the value in kJ/mol of the standard enthalpy change, ^H*, for the reaction at 298 K. ii) based on your answer to i, predict whether the temperature the contents of the insulated container will increase, decrease, or remain the same as the reaction proceeds. Justify your prediction.

i) ^H* = broken - bonded ii) decreases b/c ^H* is positive and therefore endothermic