Chemistry Midterm

0.20 M

If 200. mL of 0.60 M MgCl2(aq) is added to 400. mL of distilled water, what is the concentration of Mg2+(aq) in the resulting solution? (Assume volumes are additive).

Benzene, C6H6

If equal masses of the following compounds undergo complete combustion, which will yield the greatest mass of CO2?

CrO2

In which of the following compounds is the mass ratio of chromium to oxygen closest to 1.62 to 1.00?

(−ΔH1)+ΔH2

Reaction 1: N2O4(g)→2NO2(g) ΔH1=+57.9kJ Reaction 2: 2NO(g)+O2(g)→2NO2(g) ΔH2=−113.1kJ Based on the information for two different reactions given above, which of the following gives the quantities needed to calculate the enthalpy change for the reaction represented by the overall equation below? 2NO(g)+O2(g)→N2O4(g)

0.033 M

Solid Al(NO3)3 is added to distilled water to produce a solution in which the concentration of nitrate, [NO3-], is 0.10 M. What is the concentration of aluminum ion, [Al3+], in this solution?

The thermometer was incorrectly calibrated and read 0.5 Celsius degree too high during the procedure.

-NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq) A student is trying to determine the heat of reaction for the acid-base neutralization reaction represented above. The student uses 0.50 M NaOH and 0.50 M HCl solutions. Which of the following situations, by itself, would most likely result in the LEAST error in the calculated value of the heat of reaction? -The thermometer was incorrectly calibrated and read 0.5 Celsius degree too high during the procedure. -The volume of the acid solution added to the calorimeter was actually 1.0 mL less than what was recorded. -The calorimeter was poorly insulated, and some heat escaped to the atmosphere during the procedure. -The actual molarity of the base solution was 0.53 M but was recorded as 0.50 M. -The final temperature of the mixture was taken before the contents of the calorimeter had reached thermal equilibrium.

12

. . . C10H12O4S(s) + . . . O2(g) → . . . CO2(g) + . . . SO2(g) + . . . H2O(g) When the equation above is balanced and all coefficients are reduced to their lowest whole-number terms, the coefficient for O2(g) is

2

. . . LiHCO3(aq) + . . . H2SO4(aq) → . . . Li2SO4(aq) + . . . H2O(l) + . . . CO2(g) When the equation above is balanced and the coefficients are reduced to lowest whole-number terms, what is the coefficient of H2O(l) ?

The amount of OF2(g)OF2(g) produced is halved.

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? -The amount of OF2(g)OF2(g) produced is doubled. -The amount of OF2(g)OF2(g) produced is halved. -The amount of NaF(aq)NaF(aq) produced remains the same. -The amount of NaF(aq)NaF(aq) produced is doubled.

0.14 M

5 Fe2+ + MnO4- + 8 H+ ⇄ 5 Fe3+ + Mn2+ + 4 H2O In a titration experiment based on the equation above, 25.0 milliliters of an acidified Fe2+ solution requires 14.0 milliliters of standard 0.050-molar MnO4- solution to reach the equivalence point. The concentration of Fe2+ in the original solution is

2 Li(s) + 2 H2O(l) → 2 Li+(aq) + 2 OH−(aq) + H2(g)

A 0.35 g sample of Li(s) is placed in an Erlenmeyer flask containing 100 mL of water at 25°C. A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated. After all of the Li(s) has reacted with H2O(l), the solution in the flask is added to a clean, dry buret and used to titrate an aqueous solution of a monoprotic acid. The pH curve for this titration is shown in the diagram below. Which of the following is the balanced net-ionic equation for the reaction between Li(s) and water?

CO2

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

C2H6O

A 23.0g sample of a compound contains 12.0g of C, 3.0g of H, and 8.0g of O. Which of the following is the empirical formula of the compound?

The mass of MgMg and the mass of ClCl in the sample

A 5.0g sample of MgCl2 may contain measurable amounts of other compounds as impurities. Which of the following quantities is (are) needed to determine that the sample is pure MgCl2 ?

75%

A sample of CaCO3 (molar mass 100. g) was reported as being 30. percent Ca. Assuming no calcium was present in any impurities, the percent of CaCO3 in the sample is

3, 4, 6, 7

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?

KBr < KCl < NaCl

A student has a 1g sample of each of the following compounds: NaCl, KBr, and KCl. Which of the following lists the samples in order of increasing number of moles in the sample?

Which has the greater molar mass, X or Z?

A student has samples of two pure compounds, XClO3 and ZClO3, which contain unknown alkali metals X and Z. The student measures the mass of each sample and then strongly heats the samples to drive off all the oxygen, leaving solid residues of XCl and ZCl. The student measures the mass of the solid residue from each sample. Which of the following questions can be answered from the results of the experiment?

Which sample has the higher purity?

A student has two samples of NaCl, each one from a different source. Assume that the only potential contaminant in each sample is KCl. The student runs an experiment to determine the percent by mass of chlorine in each sample. From the results of this experiment alone, which of the following questions is most likely to be answered? -Which sample has the higher purity? -Which sample has the higher density? -What is the source of the contaminants present in each of the samples? -Which sample came from a salt mine, and which sample came from the ocean?

The mass of ClCl in each mixture

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) ?

After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.

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? -The solution does not change color after stirring. -The KCl crystals are no longer visible after mixing with water. -There is a temperature change in the solution during the dissolving process. -After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.

Molar mass of the compound, mass of the sample

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

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

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 resulting solution would contain a precipitate.

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? -The volume of the resulting solution will be equal to the sum of the volumes of the original solutions. -The mass of the resulting solution will be equal to the sum of the masses of the original solutions. -The resulting solution would contain a precipitate. -The resulting solution will be clear.

A cube of metal was changed into a flat sheet of metal.

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 cube of metal was changed into a flat sheet of metal. -When two liquids at room temperature were combined in a beaker, the beaker became hot. -When two clear liquids were combined, the resulting mixture was cloudy. -When a colorless liquid was added to a blue liquid, the resulting solution was yellow.

MgO

According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen?

2

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?

The particle volume of Ar is greater than that of Ne.

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. -Ar atoms have more valence electrons than Ne atoms have, so Ar atoms have greater interparticle forces. -The intermolecular forces between Ne atoms are greater than those between Ar atoms. -Ar atoms are more attracted to the walls of the container than Ne atoms are.

The mass is the same, since the number of each type of atom in the vessel is constant.

At 27°C, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO3(s), NaBr(s), Cu(s), or I2(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mm Hg. All four vessels are heated to 127°C and allowed to reach a constant pressure. At 127°C, the entire sample of I2 is observed to have vaporized. How does the mass of vessel 5 at 127°C compare to its mass at 27°C?

20. mol

C3H8(g) + 4 Cl2(g) → C3H4Cl4(g) + 4 HCl(g) A 6.0 mol sample of C3H8(g) and a 20. mol sample of Cl2(g) 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(g) have been produced?

12 L

CS2(l) + 3 O2(g) → CO2(g) + 2 SO2(g) What volume of O2(g) is required to react with excess CS2(l) to produce 4.0 L of CO2(g)? (Assume all gases are measured at 0°C and 1 atm.)

C4H8

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

Consider atoms of the following elements. Assume that the atoms are in the ground state. The atom that contains exactly two unpaired electrons A. S B. Ca C. Ga D. Sb E. Br

C

Consider atoms of the following elements. Assume that the atoms are in the ground state. The atom that contains only one electron in the highest occupied energy sublevel A. S B. Ca C. Ga D. Sb E. Br

C2H3O2-(aq) + H3O+(aq) → HC2H3O2(aq) + H2O(l)

Directions: Each set of lettered choices below refers to the numbered statements immediately following it. Select the one lettered choice that best fits the statement. A choice may be used once, more than once, or not at all. The following questions refer to the chemical reactions represented below. (A) 2 C6H6(l) + 15 O2(g) → 12 CO2(g) + 6 H2O(l) (B) C2H3O2-(aq) + H3O+(aq) → HC2H3O2(aq) + H2O(l) (C) 4 H+(aq) + 4 Co2+(aq) + O2(g) + 24 NH3(aq) → 4 Co(NH3)63+(aq) + 2 H2O(l) (D) CaCO3(s) → CaO(s) + CO2(g) (E) 2 H2O2(l) → O2(g) + 2 H2O(l) The reaction between a Brønsted-Lowry acid and a Brønsted-Lowry base

0.22 L of H2 has been produced.

Fe(s) + 2HCl(aq) --> FeCl2(aq) + H2(g) When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powdered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true? -HCl is in excess, and 0.100 mol of HCl remains unreacted. -HCl is in excess, and 0.020 mol of HCl remains unreacted. -0.015 mol of FeCl2 has been produced. -0.22 L of H2 has been produced.

0.22 L of H2 has been produced.

Fe(s) + 2HCl(aq) --> FeCl2(aq) +H2(g) When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powdered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true? -HCl is in excess, and 0.100 mol of HCl remains unreacted. -HCl is in excess, and 0.020 mol of HCl remains unreacted. -0.015 mol of FeCl2 has been produced. -0.22 L of H2 has been produced.

An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction.

For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation? -An exothermic chemical change occurred because heat flowed from the contents of the beaker to the room. -An exothermic physical change occurred because heat flowed from the contents of the beaker and the water on the board to the room. -An endothermic physical change occurred because the freezing of water is an endothermic process. -An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction.

14 mL

Given that the density of Hg(l) at 0°C is about 14 g mL-1, which of the following is closest to the volume of one mole of Hg(l) at this temperature?

The temperature of the reaction mixture increases.

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?

H2O(l) and Cl−(aq)

HCl(aq)+H2O(l)→H3O+(aq)+Cl−(aq) For the dissolution of HCl in water represented above, which of the following pairs includes the Brønsted-Lowry bases?

Using twice the volume of MgCl2(aq)MgCl2(aq) and twice the volume of NaOH(aq)

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?

NH3(aq) and Cl-(aq)

NH3(aq) + HCl(aq) ⇄ NH4+(aq) + Cl-(aq) The Brønsted-Lowry bases in the reaction represented above are

2Ag+(aq) + Ni(s) → 2Ag(s) + Ni2+(aq)

Ni(s)→Ni2+(aq)+2e− Ag+(aq)+e−→Ag(s) 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?

B

The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following? A. Na has a greater density at standard conditions than Ne. B. Na has a lower first ionization energy than Ne. C. Na has a higher melting point than Ne. D. Na has a higher neutron-to-proton ratio than Ne. E. Na has fewer naturally occurring isotopes than Ne.

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

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 would be the best basis for concluding that the sample was pure Te? -Te forms ions with a −2 charge, whereas I forms ions with a −1 charge. -Te is more abundant than I in the universe. -I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope. -I has a higher first ionization energy than Te does.

Water, H2O

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?

MgMg with 14 neutrons

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 26amu represents an isotope of which of the following elements?

D

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? 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.

Sr2+(aq) + SO42−(aq) → SrSO4(s)

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?

Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu, a student dissolves a small preweighed sample in HNO3(aq). Ag+(aq)and Cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process? -Centrifuging the solution to isolate the heavier ions -Evaporating the solution to recover the dissolved nitrates -Adding enough base solution to bring the pH up to 7.0 -Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

CrO3

What is the empirical formula of an oxide of chromium that is 48 percent oxygen by mass?

volume

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.

D

Which of the following ground-state electron configurations represents the atom that has the lowest first-ionization energy? A. 1s2 2s1 B. 1s2 2s2 2p2 C. 1s2 2s2 2p6 D. 1s2 2s2 2p6 3s1

NH3

Which of the following is the conjugate acid of NH2- ?

F−(aq) + H+(aq) → HF(aq)

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?

2.0g / 20.18g/mol (6.0 × 10^23 particles/mol)

Which of the following numerical expressions gives the number of particles in 2.0g of Ne?