chem final 2020

Which of the following nuclei has equal number of neutrons and protons?

24Mg

A mixture of gases, nitrogen, oxygen, and carbon dioxide at 27 °C and 0.50 atmospheres pressure occupied a volume of 492 mL. How many moles of gas are there in this sample?

A) .010

When 8.0 g of N2H4 (32 g mol-1) and 92 g of N2O4 (92 g mol-1) are mixed together and react according to the equation above, what is the maximum mass of H2O that can be produced?

A) 9.0 grams

Which of the following does NOT behave as an electrolyte when dissolved in water?

A) C6H12O6

Which of the following species is in the greatest concentration in a 0.100-molar solution of H2SO4 in water?

A) H+ ions

Which of the following has the bond angles arranged in order of decreasing polarity?

A) H-F> N-F > F-F

At point R in the titration, which of the following species has the highest concentration?

A) HA

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

Sodium bromide, NaBr

A) Lattice of positive and negative ions held together by electrostatic forces

Cesium chloride, CsCl

A) Lattice of positive and negative ions held together by electrostatic forces.

Zn(s) is used to reduce other compounds in chemical reactions. If a chemist needs a substance that is more effective in its reducing ability, which of the following species would be the best choice?

A) Na

Based on the data in the tables 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

Gases are at STP which of the following has the greatest rate of effusion through a pinhole?

A) Ne

For an ideal gas, which pair of variables are inversely proportional to each other?

A) P, V

A student carries out the same titration, but uses an indicator instead of a pH meter. If the indicator changes color slightly past the equivalence point, what will the student obtain for the calculated concentration of the acid?

A) Slightly less than .0800 M

A rigid metal tank contains oxygen gas. Which of the following applies to the gas in the tank when additional oxygen is added at constant temperature?

A) The average speed of the gas molecules remains the same

At a particular time in the reaction (Q), the concentrations of all three species was 2.0M. What must happen in order for the reaction to reach equilibrium? The value of Kc at 250C is 8.1.

A) The rate of the forward reaction would increase, and [SO3] would decrease

It is observed that the reaction producing KCl from its elements goes essentially to completion. Which of the following is a true statement about the thermodynamic favorability of the reaction?

A) The reaction is favorable and driven by an enthalpy change only

Based on the table above, which of the following correctly predicts the relative strength of the attraction of Zn+2, Ca+2 and Ba+2 ions to water molecules in solution, from strongest to weakest, and provides the correct reason?

A) Zn+2>Ca+2>Ba+2 because the smaller ions have a stronger Coulombic attraction to water

When solid ammonium chloride, NH4Cl(s) is added to water at 25 °C, it dissolves and the temperature of the solution decreases. Which of the following is true for the values of H and S for the dissolving process?

A) delta H positive, delta S positive

A sample of 0.010 mole of oxygen gas is confined at 400 K and 0.80 atm. What would be the pressure of this sample at 300 K and the same volume?

B) .60 atm

The system shown above is at equilibrium at 28 °C. At this temperature, the vapor pressure of water is 28 millimeters of mercury. The partial pressure of O2(g) in the system is

B) 133 mm Hg

If the decomposition were to go to completion, the total pressure in the container would be

B) 2.0 atm

Of the following reaction, which involves the largest decrease in Entropy?

B) 4 La + 3 O2 —> 2 La2O3

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

B) 43.7 kJ is absorbed

Which of the four acids listed in the table is hydrochloric acid?

B) Acid 2

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

B) Butane

Gold, Au

B) Closely packed lattice with delocalized electrons throughout

Silver, Ag

B) Closely packed lattice with delocalized electrons throughout

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?

B) Difference in strength between covalent bonds and intermolecular attarctions

The density of the gas, in g/L, is

B) Greatest in container C

The correct formula for hydroiodic acid is

B) HI

The net ionic equation for the reaction that occurs during the titration of nitrous acid with sodium hydroxide is

B) HNO2 + OH¯ —> NO2¯ + H2O

Which of the following statements about Kp, the equilibrium constant for the reaction, is correct?

B) Kp<1

Which of the following is the best particulate representation of the species (other than H2O) that are present in significant concentrations in the solution at point U in the titration?

B) Na, Na, Na, OH, A, A

Which of the following could be the identity of a white crystalline solid that has the following properties? It melts at 3200C. It does not conduct electricity as a solid. It conducts electricity in a solution

B) NaOH

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?

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.

Which of the values of delta H for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)?

B) Y and Z only

A 2.0mol sample of HI(aq) is added to 1.0L of H2O(l) and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium?

B) [I-]>[HI]

The reaction indicated above is thermodynamically spontaneous at 298 K, but becomes nonspontaneous at higher temperatures. Which of the following is true at 298 K?

B) delta H, delta H, and delta S are all positive

COCl2 decomposes according to the equation above. When pure COCl2(g) is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches equilibrium at 690 k, the total pressure in the flask is 1.2 atm. What is the value of Kp for the reaction at 690 K?

C) .050

A 40.0 mL sample of 0.25 M KOH is added to 60.0 mL of 0.15 M Ba(OH)2. What is the molar concentration of OH¯(aq) in the resulting solution? (Assume that the volumes are additive)

C) .28 M

A 6.0 mol sample of C3H8 and a 20. mol sample of Cl2 are placed in a previously evacuated vessel, where they react according to the equation above. After one of the reactants has been totally consumed, how many moles of HCl have been produced?

C) 20. mol

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?

C) 242 pm, 419 kJ/mol

How many milliliters of 11.6-molar HCl must be diluted to obtain 1.0 liter of 3.0-molar HCl?

C) 260 mL

Which of the following species is in the greatest concentration in a 0.100-molar solution of H2SO4 in water?

C) 260 mL

What is the pH of a 0.00030 M HNO3 solution?

C) 3.52

Using the graduated cylinder illustrated on the right, what is the most correct volume?

C) 36.5 mL

A student mixes dilute AgNO3 with excess NaCl to form AgCl, as represented by the net ionic equation above. Which of the diagrams below best represents the ions that are present in significant concentrations in the solution? (Ksp for AgCl is 1.8 x 10^-10)

C) 4 Na, 2 Cl, 2 NO3

In 1.00 mol of potassium zirconium sulfate trihydrate: K4Zr(So4)4 x 3H2O

C) 4 x 6.02 x 10^23

The figure above represents three sealed 1.0 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?

C) 4.5 atm

Which of the following particulate diagrams best shows the formation of water vapor from hydrogen gas and oxygen gas in a rigid container at 125C?

C) 6 and 3 to 6 H2Os

The molar mass of (NH4)2S is closest to

C) 68 g/mol

A measured mass of an unreactive metal was dropped into a small graduated cylinder half filled with water. The following measurements were made. Mass of metal = 19.611 grams Volume of water before addition of metal = 12.4 milliliters Volume of water after addition of metal = 14.9 milliliters ​​Using correct sig figs the density of the metal should be reported as:

C) 7.8 grams/mL

Which of the following is the most likely cause for the increase in pressure observed in the container as the reaction reaches equilibrium?

C) An increase in the number of molecules, which increases the frequency of collisions with the walls of the container

Which diagram depicts an alloy of Manganese and Zinc?

C) Black and white circles

An organic compound which has the empirical formula CHO has a molar mass of 58. Its molecular formula is:

C) C2H2O2

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?

C) C4H8

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

C) CH3OH

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

C) CH4

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. Where do you expect the gas to meet?

C) Closer to the HCl end

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?

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

The atom that contains only one electron in its highest occupied energy sublevel

C) Ga

All the reactions represented above occur in an aqueous solution of oxalic acid. Which of the following represent a Bronsted-Lowry conjugate acid-base pair?

C) HC2O4 and C2O4

The elements I and Te have similar average atomic masses. A sample that was believed tot 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 would be the best basis for concluding that the sample was pure Te?

C) I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope

The diagram above shows molecules of Br2 and I2...

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

A sample of an ideal gas is cooled from 50.0 °C to 25.0 °C in a sealed container of constant volume. Which of the following values for the gas will decrease?

C) III only

At room temperature I2(s) is a molecular solid. Which of the following provides a characteristic of I2(s) with a correct explanation?

C) It is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs.

What can be inferred about S0 for the reaction at 600K?

C) It must be positive, since G0 is negative and H0 is positive.

A compound contains 1.10 mol of K, 0.55 mol of Te, and 1.65 mol of 0. What is the simplest (empirical) formula of this compound?

C) K2TeO3

What remains in the reaction vessel after equal masses of K and Cl2 have reacted until either one or both of the reactants have been completely consumed?

C) KCl and Cl2 only

Which of the following is a liquid in its standard state at 298 K (room remperature)?

C) Mercury

Which one of the following orderings of lattice energy is correct for these ionic compounds?

C) ScN>MgO>NaCl>CsI

Methane, CH4

C) Strong single covalent bonds with weak intermolecular forces.

At which point on the titration curve is [A-1] closest to twice that of [HA]?

C) T

Nonane and 2, 3, 4-trifluoropentane have almost identical molar masses, but nonane has a significantly higher boiling point. Which of the following statements bets helps explain this observation?

C) The carbon chains are longer in nonane than they are in 2, 3, 4-trifluoropentane

A 25 ml sample of a 1.0 M solution of acid 1 is mixed with 25 ml of 0.50 M NaOH. Which of the following best explains what happens to the pH of the mixture when a few drops of 1.0 M HNO3 are added?

C) The pH of the mixture stays about the same, because the conjugate base of Acid 1 reacts with the added H3O ions

What happens to the temperature of the contents of the vessel as the reaction occurs?

C) The temperature must decrease, because the reaction is endothermic

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?

C) Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule

Which of the following is the best piece of laboratory glassware for preparing 500mL off a solution?

C) Volumetric flask

A solution of a salt of a weak acid HY is added to a solution of another weak acid HX. Based on the information given above, which of the following species is the strongest base?

C) Y-

Caffeine (C8H10N4O2) is a weak base with a Kb value of 4x10-4. The pH of a 0.01 M solution of caffeine is in the range of

D) 11-12

Beaker X and 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 the volumes are additive, which of the following sets of solutions could be represented by the diagram above?

D) 2.0 M AgNO3, 1.0 M MgCl2, .50 M Mg(NO3)2 and AgCl

What number of moles of O2 are needed to produce 142 grams of P4O10 from P? (Molecular mass P4O10 = 284)

D) 2.5 moles

Based on the information above, what is the enthalpy change for the sublimation of iodine I2(s) → I2(g)

D) 62 kJ/molrxn

Which of the following statements about atoms is NOT correct?

D) All atoms of a given element must have the same number of protons, neutrons, and electrons

If equal volumes of the four acids at a concentration of 0.50 M are each titrated with a strong base, which will require the greatest volume of base to reach the equivalence point?

D) All the acids will require the same volume of base to reach the equivalence point

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

D) CH2F

What is the formula of the ionic compound formed between Ca and P?

D) Ca3P2

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

D) D

A kinetics experiment is set up to collect the gas that is generated when a sample of chalk, consisting of primarily CaCO3, is added to a solution of ethanoic acid, CH3COOH. The rate of reaction between CaCO3 and CH3COOH is determined by measuring the volume of gas generated at 25C and 1 atm as a function of time. Which of the following experimental conditions is most likely to increase the rate of production?

D) Decreasing the particle size of the CaCO3 by grinding it into a fine powder

According to the VSEPR model, the progressive decrease in the bond angles in the series of molecules CH4, NH3, H2O is best accounted for by the ...

D) Increasing number of the unshared pairs of electrons

Oxygen, O2

D) Molecule with strong multiple covalent bonds

Which of the following compounds is ionic and contains sigma (σ) and pi (π) covalent bonds?

D) NaCN

The photoelectron 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?

D) Nitrogen atoms have a smaller nuclear charge than oxygen atoms

In which of the following does sulfur have the same oxidation number as in H2SO4?

D) SO2Cl2

Carbon dioxide, CO2

D) Strong multiple covalent bonds (including bonds.) with weak intermolecular forces

The mass spectrum of element X as represented above. Which of the following can be concluded about element X?

D) The atomic mass of X is between 90 and 92

Examining data obtained from mass spectrometry supports which of the following?

D) The existence of isotopes

Which of the following is true regarding the reaction represented above?

D) The oxidation number of Se changes from -2 to +6.

The graph above shows the speed distribution of molecules in a sample of gas at a certain temperature. Which of the following graphs shows the speed distribution of the same molecules at a lower temperature (as a dashed curve)?

D) Up faster and down faster

Which if the following correctly ranks the three monoprotic acids listed in the table above from weakest to strongest?

D) Z<Y<X

A student mixes equal volumes of 1.0M solutions of tin (II)chloride and copper(II)sulfate and observes that no precipitate forms. The student mixes equal volumes of 1.0M solutions of zinc (II)sulfate and tin(II)fluoride and observes the formation of a precipitate. The formula of the precipitate must be

D) ZnF2

Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are

D) different because S has a greater number of electron domains (regions of electron density) surrounding it than C has

The average kinetic energy of the gas molecules is

D)The same in all three containers

As the reaction progresses toward equilibrium, the rate of the forward reaction

Decreases to become a constant nonzero rate at equilibrium

The BCl3 molecule has trigonal planar structure. The hybridization of the B orbitals should be

a) sp2

Which of these lines represents the most energetic light?

A) 837.761 nm

For which acid is the value of the acid-dissociation constant, Ka, the smallest?

A) Acid 1

The atom that contains exactly two unpaired electrons

A) S

Reacts with water to form a strong base

A) Strontium oxide

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 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, H2O

All the reactions represented above occur in an aqueous solution of oxalic acid. Which of the following represent a Bronsted-Lowry conjugate acid-base pair?

B) HC2O4 and C2O4

Which of the following particulate diagrams best shows the formation of water vapor from hydrogen gas and oxygen gas in a rigid container at 125C?

C) 6 and 3 becomes 6 H2Os

What is the percent hydrogen (by mass) in ammonium carbonate, (NH4)2CO3?

C) 8.3%

Of the following species, which has the greatest concentration in a 1.0 M solution of acid 1 at equilibrium?

C) Acid 1

A hydrocarbon gas with an empirical formula CH2 has a density of 1.88 grams per liter at 0 °C and 1.00 atmosphere. A possible formula for the hydrocarbon is

C) C3H6

Copper (II) sulfite solution is heated strongly with concentrated hydrochloric acid. The products of this reaction are

C) Cu2+, Cl-, SO2, H2O

The table above shows the values of Ka for four weak acids. Which of the following pairs of chemical species, when combined in equilmolar amounts, results in a buffer with a pH closest to 7.5?

C) HClO and ClO-

What is the expression for the equilibrium constant Kc?

C) [O2][SO2]^2/[SO3]^2

Which of the following expressions is equivalent to delta H for the reaction represented above?

C) x+2y

Which of the following has the lowest conductivity?

D) 0.1 M HF

Caffeine (C8H10N4O2) is a weak base with a Kb value of 4 x 10-4. The pH of a 0.01 M solution of caffeine is in the range of

D) 11-12

Which of the following contains polar bonds but is nonpolar?

D) CF4

Which of the following changes to the system would cause decrease the concentration of K+ ions from equilibrium?

D) Temperature of the solution is increased

A hot-air balloon rises. Which of the following is the best explanation for this observation?

D) The air density inside the balloon is less than that of the surrounding air

CH3CH2OH boils boils at 78 °C and CH3OCH3 boils at - 24 °C, although both compounds have the same composition. This difference in boiling points may be attributed to a difference in

D) hydrogen bonding

The correct formula for dinitrogen pentoxide is

N2O5