AP Chem-first quiz

Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms?

B

If the pressure of each gas is increased at constant temperature until condensation occurs, which gas will condense at the lowest pressure?

Butane

Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces?

CH3OH(l)

Based on the information in the table above, which liquid, CS2(l) or CCl4(l), has the higher equilibrium vapor pressure at 25°C, and why?

CS2(l), because it has weaker London dispersion forces

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?

Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy.

The diagram above shows a thin-layer chromatogram of a mixture of products from a chemical reaction. The separation was performed using 50% ethyl acetate in hexane as the solvent (mobile phase) and silica gel as the polar stationary phase. On the basis of the chromatogram and the information about solvents in the table above, which of the following would be the best way to decrease the distance that the products travel up the plate?

Decrease the percentage of ethyl acetate in the solvent.

The survival of aquatic organisms depends on the small amount of O2 that dissolves in H2O. The diagrams above represent possible models to explain this phenomenon. Which diagram provides the better particle representation for the solubility of O2 in H2O, and why?

Diagram 2, because the polar H2O molecules can induce temporary dipoles on the electron clouds of O2 molecules.

A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs?

Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces

Which of the following techniques is most appropriate for the recovery of solid KNO3 from an aqueous solution of KNO3?

Evaporation to dryness

At 298 K and 1 atm, bromine is a liquid with a high vapor pressure, whereas chlorine is a gas. This provides evidence that, under these conditions, the

Forces among Br2 molecules are greater than those among Cl2 molecules

The London (dispersion) forces are weakest for which of the following gases under the same conditions of temperature and pressure?

H2

Is a strong electrolyte in aqueous solution?

HBr(g)

The liquefied hydrogen halides have the normal boiling points given above. The relatively high boiling point of HF can be correctly explained by which of the following?

HF molecules tend to form hydrogen bonds.

Of the following, the best explanation for the fact that most gases are easily compressed is that the molecules in a gas

Have a real, nonzero volume

Which of the following describes the changes in forces of attraction that occur as H2O changes phase from a liquid to a vapor?

Hydrogen bonds between H2O molecules are broken.

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 59oC and 184oC, respectively?

I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2.

The electron cloud of HF is smaller than that of F2 , however, HF has a much higher boiling point than F2 has. Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HF?

Liquid F2 has weak dispersion force attractions between its molecules, whereas liquid HF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.

In solid methane, the forces between neighboring CH4 molecules are best characterized as

London (dispersion) forces

Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C?

NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3.

Based on Coulomb's Law and the information in the table above, which of the following cations is most likely to have the weakestinteraction with an adjacent water molecule in an aqueous solution?

Na+

Which of the following substances is a strong electrolyte when dissolved in water?

Sodium Nitrate

The boiling points of the elements helium, neon, argon, krypton, and xenon increase in that order. Which of the following statements accounts for this increase?

The London (dispersion) forces increase.

Four different liquid compounds in flasks at 20°C are represented above. The table below identifies the compounds. Flask C shows the most particles in the vapor phase. Which of the following is not shown in the model but best helps to explain why flask C must contain pentane?

The strength of the intermolecular forces between the particles in the liquids

In a paper chromatography experiment, a sample of a pigment is separated into two components, X and Y, as shown in the figure above. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results?

Y is more polar than X

In the diagram above, which of the labeled arrows identifies hydrogen bonding in water?

D

Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds. Which of the following diagrams shows the correct representation of the hydrogen bonding (denoted by dashed lines) between thymine and adenine base pairs? (In each diagram, thymine is shown at the left and adenine is shown at the right. The bases are attached to the backbone portion of the DNA strands.)

D

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?

Zn2+ > Ca2+ > Ba2+ because the smaller ions have a stronger coulombic attraction to water

The best explanation for the fact that diamond is extremely hard is that diamond crystals

are giant molecules in which each atom forms strong covalent bonds with all of its neighboring atoms

The mass spectrum of the element Sb is most likely represented by which of the following?

B

The structure of one form of boron nitride is represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

In which of the following processes are covalent bonds broken?

C(diamond) → C(g)

A student obtains a liquid sample of green food coloring that is known to contain a mixture of two solid pigments, one blue and one yellow, dissolved in an aqueous solution of ethanol. Which of the following laboratory setups is most appropriate for the student to use in order to separate and collect a substantial sample of each of the two pigments?

D

A student places a piece of I2(s) in 50.0 mL of H2O(l), another piece of I2(s) of the same mass in 50.0 mL of C6H14(l), and shakes the mixtures. The results are shown above. What do the results indicate about the intermolecular interactions of the substances?

I2 and C6H14 have similar intermolecular interactions, and I2 and H2O do not.

The diagram above is a molecular model of a gaseous diatomic element that is just above its boiling point. Intermolecular forces between the gas molecules will cause them to condense into the liquid phase if the temperature is lowered. Which of the following best describes how the model is limited in its depiction of the phenomenon?

It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.

Based on the data in the tables above, which of the following statements provides the best prediction for the boiling point of NaCl ?

NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?

The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.

Benzene, C6H6 , has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best describes the intermolecular forces of attraction between water and benzene?

There are dipole-induced dipole and London dispersion interactions between water and benzene.