AP Chem midterm- JOINED
The diagram above shows the distribution of speeds for a sample of N2(g) at 25°C. Which of the following graphs shows the distribution of speeds for a sample of O2(g) at 25°C (dashed line) ?
A)
A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?
A) A cube of metal was changed into a flat sheet of metal
When the chemical reaction 2NO(g)+O2(g)→2NO2(g) is carried out under certain conditions, the rate of disappearance of NO(g) is 5.0×10−5 Ms−1. What is the rate of disappearance of O2(g) under the same conditions?
A) Because two molecules of NO are consumed per molecule of O2, the rate of disappearance of O2(g) is 2.5 x 10-5 Ms-1
The oxidation of NO(g) producing NO2(g) is represented by the chemical equation shown above. The initial concentrations of NO and O2 are given in the table above. The changes in the concentration of NO(g) as a function of time are shown in the following graph. Under the same conditions, one of the following graphs represents the changes in the concentration of O2(g) over the same period of time. Which graph best represents the changes in concentration of O2(g), and why?
A) Graph 1, because the rate of O2 consumption is half the rate at which NO is consumed; two molecules of NO react for each molecule of O2 that reacts.
Which statement correctly compares what occurs when molecules absorb photons in the microwave region with what occurs when molecules absorb photons in the infrared region?
A) Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states
Equal volumes of 0.2M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?
A) Pb2+(aq) + 2Br-(aq) --> PbBr2(s)
C6H12O6+ 602 --> 6CO2 + 6H2O The reaction between C6H12O6 and O2 is represented by the balanced equation above. In an experiment, 0.30mol of CO2 was produced from the reaction of 0.05mol of C6H12O6 with excess O2. The reaction was repeated at the same temperature and in the same container, but this time 0.60mol of CO2 was produced. Which of the following must be true?
A) The initial amount of C6H12O6 in the container must have been 0.10 mol.
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?
B)
The complete photoelectron spectrum of an element is given above. Which of the following electron configurations is consistent with the spectrum?
B) 1s2 2s2 2p6 3s2 3p3
Al(s)→Al3+(aq)+3e− Zn2+(aq)+2e−→Zn(s) The half-reactions for the oxidation-reduction reaction between Al(s) and Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients?
B) 2
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?
B) Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles
The ionic compounds NaCl and MgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why?
B) Diagram 1 represents NaCl; it has a lower melting point than MgS because the coulombic attractions between its singly charged Na+ ions and the Cl- ions are weaker than those between the ions in MgS
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?
B) I2 and C6H14 have similar intermolecular interactions, and I2 and H2O do not
NH4+(aq) + OH-(aq) --> NH3 (aq) + H2O (l) When 0.20 M NH4Cl(aq) and 0.20 M NaOH(aq) are mixed, the reaction represented by the equation above occurs and a strong smell of ammonia, NH3, is observed. Based on this information, which of the following statements is true?
B) NH4+ (aq) is a stronger acid than H2O(l) is
The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10−19J. Using the wavelength information provided above, what is the color of the light?
B) ORANGE
The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?
B) Sr2+(aq) + SO4 2-(aq) --> SrSO4(s)
2F2(g)+2NaOH(aq)→OF2(g)+2NaF(aq)+H2O(l) A 2mol sample of F2(g) reacts with excess NaOH(aq) according to the equation above. If the reaction is repeated with excess NaOH(aq) but with 1 mol of F2(g), which of the following is correct?
B) The amount of OF2(g) produced is halved
The elements C and Se have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from C and Se is most likely to be true?
B) The carbon-to-selenium bond is nonpolar covalent
Infrared spectroscopy is a useful tool for scientists who want to investigate the structure of certain molecules. Which of the following best explains what can occur as the result of a molecule absorbing a photon of infrared radiation?
B) The energies of infrared photons are in the same range as the energies associated with different vibrational states of chemical bonds. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the types and strengths of different bonds in the molecules
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?
B) The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance
HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l) A student had two dilute, colorless solutions, HCl(aq) and NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?
B) The temperature of the reaction mixture increases
A student is given two 10g samples, each a mixture of only NaCl(s) and KCl(s) but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of KCl(s) ?
B. The mass of Cl in each mixture
Steel is an alloy containing Fe atoms and C atoms. Which of the following diagrams best represents the particle-level structure of steel?
BIG FE SMALL C
The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10−19J. Which of the following is closest to the frequency of the light with photon energy of 3.3×10−19J?
C) 5.0 x 10^14 s-1
The initial rate of formation of CO2(g) from the chemical reaction represented by the equation above was studied in two separate experiments. The table above provides the experimental conditions used. If both experiments are carried out with finely powdered samples of the solid and 50.0mL of HCl(aq), which experiment, if any, will have the faster initial rate of formation of CO2(g) and why?
C) CO2(g) will be formed at a faster rate in experiment 2 because more H+ particles can react per unit time.
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?
C) Diagram 2, because the polar H2O molecules can induce temporary dipoles on the electron clouds of O2 molecules
The complete photoelectron spectrum for an element is shown above. Which of the following observations would provide evidence that the spectrum is consistent with the atomic model of the element?
C) In its compounds, the element tends to form ions with a charge of +1.
Two pure elements react to form a compound. One element is an alkali metal, X, and the other element is a halogen, Z. Which of the following is the most valid scientific claim that can be made about the compound?
C) It contains ionic bonds.
Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not?
C) It does not conduct electricity because its ions cannot move freely within the solid.
Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C
C) NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3
A student was asked to formulate a hypothesis about what would happen if 100.mL of 0.1MNaOH(aq) at 25°C was combined with 100.mL of 0.1MMgCl2(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?
C) The resulting solution would contain a precipitate
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?
C) The strength of the intermolecular forces between the particles in the liquids
A sample of carbonate rock is a mixture of CaCO3 and MgCO3. The rock is analyzed in a laboratory, and the results are recorded in the table above. Which columns in the table provide all the information necessary to determine the mole ratio of Ca to Mg in the rock?
C. 3,4,6,7
The particle diagram above represents an aqueous solution of a weak monoprotic acid. The white circles represent H atoms. Which of the following shows the species that act as a Brønsted-Lowry base and its conjugate acid, in that order, in the solution?
D)
Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag+(aq) and Ni(s) based on the half-reactions represented above?
D) 2 Ag+(aq) + Ni(s) --> 2 Ag(s) + Ni2+(aq)
A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. A wavelength of 510nm corresponds to an approximate frequency of 6×1014s−1. What is the approximate energy of one photon of this light?
D) 4 x 10^-19 J
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?
D) After the water has evaporated, the white crystals in the beaker have a mass of 20.0g
Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?
D) F-(aq) + H+(aq) --> HF(aq)
HCl (aq) + H2O (l) --> H30+ (aq) + Cl-(aq) For the dissolution of HCl in water represented above, which of the following pairs includes the Brønsted-Lowry bases?
D) H2O (l) and Cl- (aq)
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?
D) It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.
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?
D) 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.
The table above summarizes data given to a student to evaluate the type of change that took place when substance X was mixed with water. The student claimed that the data did not provide enough evidence to determine whether a chemical or physical change took place and that additional tests were needed. Which of the following identifies the best way to gather evidence to support the type of change that occurred when water and X were mixed?
D) Measuring the electrical conductivities of X and the mixture of water of X
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?
D) The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined
The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaF and MgF2 is shown in the table above. On the basis of Coulomb's law, which of the following best helps to explain the large difference between the lattice energies of NaF and MgF2 ?
D) The charge of the Mg cation is larger than that of the Na cation.
The photoelectron spectrum for the element nitrogen is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom?
D) The electrons in the 2s sublevel have the smallest binding energy.
The graph above shows the distribution of molecular speeds for four different gases at the same temperature. What property of the different gases can be correctly ranked using information from the graph, and why?
D) The molecular masses of the gases, because the gas molecules have the same average kinetic energy and mass can be calculated using the equation KEavg = 1/2 mv^2
MgCl2(aq)+2NaOH(aq)→2NaCl(aq)+Mg(OH)2(s) A 100mL sample of 0.1MMgCl2(aq) and a 100mL sample of 0.2MNaOH(aq) were combined, and Mg(OH)2(s) precipitated, as shown by the equation above. If the experiment is repeated using solutions of the same molarity, which of the following changes in volume will double the amount of Mg(OH)2(s) produced?
D) Using twice the volume of MgCl2(ag) and twice the volume of NaOH
Which of the following best helps explain why the electronegativity of Cl is less than that of F?
When Cl and F form bonds with other atoms...
Beta-carotene is an organic compound with an orange color. The diagram above shows the ultraviolet spectrum of beta-carotene. Which of the following statements is true about the absorption bands in the spectrum?
c) The two main absorption bands are associated with transitions in electronic energy levels. The band in the region corresponding to shorter wavelengths shows a lower absorbance than the band in the region corresponding to longer wavelengths.
All the chlorides of the alkaline earth metals have similar empirical formulas, as shown in the table above. Which of the following best helps to explain this observation?
c) The two valence electrons of alkaline earth metal atoms are relatively easy to remove.
A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are
c) equally shared and form nondirectional bonds
Which of the following scientific claims about the bond in the molecular compound HF is most likely to be true?
d) The bond is highly polar.