AP Chemistry Questions

a physical change occurs when a substance undergoes a change in _______________ but not a change in composition.

appearance

the most common physical changes are ________________________.

phase changes

what is a generic reaction that yields hydrogen gas?

acid + metal -> salt + hydrogen gas

what is a generic reaction that yields carbon dioxide gas?

acid + carbonate -> salt + water + carbon dioxide

the half-reactions for the oxidation-reduction reaction between Co (s) and Ag+ (aq) are: Co (s) --> Co2+ (aq) + 2 e- and Ag+ (aq) + e- --> Ag (s)

a.) which substance is being oxidized and which substance is being reduced?

b.) write the balanced net ionic equation for the oxidation-reduction reaction based on the half-reactions above

a.) Co is oxidized and Ag is reduced
b.) Co (s) + 2 Ag+ (aq) --> Co2+ (aq) + 2 Ag (s)

the reaction between solid aluminum and aqueous nickel (II) nitrate is represented by the equation: Al (s) + Ni(NO3)2 (aq) --> Al(NO3)3 (aq) + Ni (s)

a.) write the oxidation half-reaction and reduction half-reaction

b.) write the balanced net ionic equation for the oxidation-reduction reaction shown above

a.) oxidation half-reaction: Al (s) --> Al3+ (aq) + 3 e-
reduction half-reaction: Ni2+ (aq) + 2 e- --> Ni (s)
b.) 2 Al (s) + 3 Ni2+ (aq) --> 2 Al3+ (aq) + 3 Ni (s)

when a substance undergoes a physical process, the composition of that substance DOES/DOESN'T change

doesn't

occurs when substance undergoes a change in properties but not in composition (ex: phase change)

physical change

occurs when substances are transformed into new substances, typically with different compositions; involves breaking and/or formation of chemical bonds

chemical change

are heat, light, formation of a precipitate, formation of a gas, and/or color change a sign of a physical or chemical change?

chemical change

a student is asked to form a hypothesis about what would happen to sodium metal when it is placed in water. which of the following hypotheses indicates that the student thinks a CHEMICAL change will occur?
a) if sodium is added to water, it will dissolve
b) if sodium is added to water, heat and light will be released
c) if sodium is added to water, the total mass will be the same
d) if sodium is added to water, the water will remain a clear, colorless liquid

b

true or false: mass and matter are conserved in physical and chemical reactions

true

...Ca3(PO4)2 + ...H3PO4 --> ...Ca(H2PO4)2
when the equation above is balanced and all coefficients are reduced to lowest whole-number terms, what is the coefficient for H3PO4?

4

write a balanced chemical equation for the dissolution of Ca(OH)2 in pure water

Ca(OH)2 --> Ca2+ + 2 OH-

a student mixes 20.0g of white KCl crystals with distilled water in a beaker. after the mixture was stirred, no crystals are visible and the solution is clear. after several days, all of the water evaporates and white crystals are found in the beaker. which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?
a) the solution does not change color
b) the KCl crystals are no longer visible after mixing w/ H2O
c) there is a temperature change during the dissolving process
d) after the water has evaporated, the white crystals in the beaker have a mass of 20.0 g

d

a reaction involving the transfer of one or more electrons between reactants

redox reaction

what is the oxidation number for oxygen (except in peroxides when it's -1)?

-2

NH3 (aq) + HCl (aq) --> NH4+ (aq) + Cl- (aq)
the Bronsted-Lowry bases in the reaction are...
a) NH3 and NH4+ b) NH3 and Cl- c) NH3 and HCl d) HCl and NH4+ e) HCl and Cl-

b

Cu (s) + 2 AgNO3 (aq) --> Cu(NO3)2 (aq) + 2 Ag (s)

the reaction between solid copper and aqueous silver nitrate produces solid silver and a blue solution, as represented by the balanced equation shown above. based on the balanced equation, which of the following identifies the oxidation and reduction half-reactions?
a) oxidation half-reaction: Cu (s) --> Cu+ (aq) + e- reduction half-reaction: Ag2+ (aq) + 2 e- --> Ag (s)
b) oxidation half-reaction: Cu (s) --> Cu2+ (aq) + 2 e- reduction half-reaction: Ag+ (aq) + e- --> Ag (s)
c) oxidation half-reaction: Ag+ (aq) + e- --> Ag (s) reduction half-reaction: Cu (s) --> Cu2+ (aq) + 2 e-
d) oxidation half-reaction: Ag2+ (aq) + 2 e- --> Ag (s) reduction half-reaction: Cu (s) --> Cu+ (aq) + e-

b

reaction between an acid & base to produce water and a salt

neutralization reaction

When the actual gas volume is greater than the volume predicted by the ideal gas law, the explanation lies in the fact that the ideal gas law does NOT include a factor for molecular.

volume

The table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4. The best explanation for the lower pressure in container 4 is that SO2 molecules

have stronger intermolecular attractions than the other three gases

Which of the following gases deviates most from ideal behavior?

SO2

A gas mixture at 0°C and 1.0atm contains 0.010mol of H2, 0.015mol of O2, and 0.025molof N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture?

About 0.20atm, because H2 comprises 20% of the total number of moles of gas.

At standard temperature and pressure, a 0.50 mol sample of H2 gas and a separate 1.0 mol sample of O2 gas have the same

average molecular kinetic energy

The distribution of speeds of H2(g) molecules at 273 K and 1 atm is shown in the diagram above. Which of the following best shows the speed distribution of He(g) atoms under the same conditions of temperature and pressure?

He will have larger bump as it has a larger molar mass

A 2 L container will hold about 4 g of which of the following gases at 0°C and 1 atm?

CO2

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

are relatively far apart

Ar(g) deviates more from ideal behavior at extremely high pressures than Ne(g) does. Which of the following is one reason for this difference?

the particle volume of Ar is greater than that of Ne

in which flask has the greatest average speed?

largest temperature, smallest pressure

in which flask has the highest density?

highest pressure temp ratio

in which flask has the smallest number of moles of gas

largest temperature, smallest pressure

When a sample of oxygen gas in a closed container of constant volume is heated until its absolute temperature is doubled, which of the following is also doubled

the pressure of the gas

A vessel contains Ar(g) at a high pressure. Which of the following statements best helps to explain why the measured pressure is significantly greater than the pressure calculated using the ideal gas law?

The combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container.

Equal masses of He and Ne are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 6 atm?

5 atm

A 2 L sample of N2(g) and a 1 L sample of Ar(g), each originally at 1 atm and 0°C, are combined in a 1 L tank. If the temperature is held constant, what is the total pressure of the gases in the tank?

3 atm

A sealed vessel contains 0.200 mol of oxygen gas, 0.100 mol of nitrogen gas, and 0.200 mol of argon gas. The total pressure of the gas mixture is 5.00 atm. The partial pressure of the argon is

2 atm

A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. The temperature is kept constant. Which of the following statements about combining the gases is correct?

The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.

The ideal gas law best describes the properties of which of the following gases at 0°C and 1 atm?

N2

Which of the following behaves most like an ideal gas at the conditions indicated?

H2(g) molecules at 10-3 atm and 200oC

A compound is heated to produce a gas whose molecular weight is to be determined. The gas is collected by displacing water in a water-filled flask inverted in a trough of water. Which of the following is necessary to calculate the molecular weight of the gas, but does NOT need to be measured during the experiment?

vapor pressure of the water

A certain crystalline substance that has a low melting point does not conduct electricity in solution or when melted. This substance is likely to be

a molecular solid

When 6.0 L of He(g) and 10. L of N2(g), both at 0°C and 1.0 atm, are pumped into an evacuated 4.0 L rigid container, the final pressure in the container at 0°C is

4.0 atm

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

Which of the following aqueous solutions has the lowest freezing point?

(A)0.2 m NaCl
(B) 0.2 m CaCl2
(C) 0.2 m H2SO4
(D) 0.2 m NH3
(E) 0.2 m Al(NO3)3

4 NH3(g) + 3 O2(g) —> 2 N2(g) + 6 H2O(g)

If the standard molar heats of formation of
ammonia, NH3(g), and gaseous water, H2O(g), are -46 kJ/mol and -242 kJ/mol, respectively, what is the value of ΔH for the reaction represented above?

(A) -190 kJ/mol
(B) -290 kJ/mol
(C) -580 kJ/mol
(D) -1,270 kJ/mol
(E) -1,640 kJ/mol

Which of the molecules represented below
contains carbon with sp2 hybridization?

(A) CH4
(B) CH2Cl2
(C) C2H6
(D) C2H2Cl2
(E) C2H4Cl2

A chemical supply company sells a concentrated solution of aqueous H2SO4 (molar mass 98 g mol−1) that is 50. percent H2SO4 by mass. At 25°C, the density of the solution is 1.4 g mL−1. What is the molarity of the H2SO4 solution at 25°C?

7.1 M

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

are relatively far apart

1/2 H2(g) + 1/2 I2(s) —> HI(g) ΔH = 26 kJ/mol
1/2 H2(g) + 1/2 I2(g) —> HI(g) ΔH = -5.0 kJ/mol

Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below?

I2(s) → I2(g)

(A) 15 kJ/mol
(B) 21 kJ/mol
(C) 31 kJ/mol
(D) 42 kJ/mol
(E) 62 kJ/mol

Which of the following compounds is LEAST likely to exist?

(A) PCl5
(B) PBr3
(C) NF3
(D) NI5
(E) SbF5

Which of the following compounds contains both ionic and covalent bonds?

(A) SO3
(B) C2H5OH
(C) MgF2
(D) H2S
(E) NH4Cl

Which of the following molecules is nonpolar but has polar covalent bonds?

(A) N2
(B) H2O2
(C) H2O
(D) CCl4
(E) CH2Cl2

In which of the following liquids do the intermolecular forces include dipole-dipole forces?

(A) F2(l)
(B) CH4(l)
(C) CF4(l)
(D) CH2F2(l)

A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance?

(A) Ionic bonds
(B) Metallic bonds
(C) Covalent bonds
(D) Hydrogen bonds

Which of the following arranges the molecules N2 , O2 , and F2 in order of their bond enthalpies, from least to greatest?

(A) F2<O2<N2
(B) O2<N2<F2
(C) N2<O2<F2
(D) N2 < F2 < O2

Element - Electronegativity

H - 2.1

C - 2.5

S - 2.5

F - 4.0

Cl - 3.0

Si - 1.8


On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity?

(A) CH4 < SiCl4 < SF4
(B) CH4 < SF4 < SiCl4
(C) SF4 < CH4 < SiCl4
(D) SiCl4 < SF4 < CH4

Which of the following Lewis electron-dot diagrams represents the molecule that contains the smallest bond angle?

(A) CF4
(B) NF3
(C) SO3
(D) SO2

The lattice energy of a salt is related to the energy required to separate the ions. For which of the following pairs of ions is the energy that is required to separate the ions largest? (Assume that the distance between the ions in each pair is equal to the sum of the ionic radii.)

(A) Na+(g) and Cl−(g)
(B) Cs+(g) and Br−(g)
(C) Mg2+(g) and O2−(g)
(D) Ca2+(g) and O2−(g)

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

The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points?

(A) Butane < 1-propanol < acetone
(B) Butane < acetone < 1-propanol
(C) 1-propanol < acetone < butane
(D) Acetone = butane < 1-propanol

K(s) + 1/2 Cl2(g) —> KCl(s) ∆H° = −437 kJ/mol

How much heat is released or absorbed when 0.050 mol of Cl2(g) is formed from KCl(s)?

(A) 87.4 kJ is released
(B) 43.7 kJ is released
(C) 43.7 kJ is absorbed
(D) 87.4 kJ is absorbed

(A) H2O
(B) NH3
(C) BH3
(D) CH4
(E) SiH4

4. Has two lone pairs of electrons
5. Has a central atom with less than an octet of electrons
6. Is predicted to have the largest bond angle
7. Has a trigonal-pyramidal molecular geometry

4. A
5. C
6. C
7. B

2 NH3(g) → 3 H2(g) + N2(g) ∆H

(A) −92 kJ/mol
(B) −46 kJ/mol
(C) 46 kJ/mol
(D) 92 kJ/mol
(E) 184 kJ/mol

describe the four main processes that occur in a mass spectrometer

1. ionization: electrons are knocked off sample particles to form mostly +1 ions

2. acceleration: ions move through a series of charged plates to form a narrow beam of high speed particles with equal kinetic energy

3. deflection: ions are attracted to the negative side of the electromagnetic field causing separation of the mixture based on mass and charge

4. detection: ions collide with a metal plate, electrons are transferred from the metal to the ion, producing a current, and a signal is sent to a computer

= number of protons - number of inner electrons

core charge

mathematically relate ionization energy, kinetic energy, and photon energy in photoelectron spectroscopy

IE = KE(photon) - KE(electron)