Unit 4: Chemical Reactions

5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) Which element is being oxidized during the titration, and what is the element's change in oxidation number? A Oxygen, which changes from -1 to 0 B Oxygen, which changes from 0 to -2 C Manganese, which changes from -1 to +2 D Manganese, which changes from +7 to +2

A

. 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) ? A: 1 B: 2 C: 3 D: 4 E: 5

B

A sample of a compound that contains only the elements C, H, and N is completely burned in O2 to produce 44.0 g of CO2, 45.0 g of H2O, and some NO2 . A possible empirical formula of the compound is A CH2N B CH5N C C2H5N D C3H3N2

B

. . . Ca3(PO4)2(s) + . . . H3PO4(l) → . . . Ca(H2PO4)2(s) When the equation above is balanced and all coefficients are reduced to lowest whole-number terms, what is the coefficient for H3PO4(l) ? A: 1 B: 2 C: 3 D: 4 E: 5

D

...C3H8(g) + ...O2(g) → ...H2O(g) + ...CO2(g) When the equation for the reaction represented above is balanced and all coefficients are reduced to the lowest whole-number terms, the coefficient for O2(g) is A: 1 B: 2 C: 3 D: 5 E:6

D

H2Se(g) + 4 O2F2(g) → SeF6(g) + 2 HF(g) + 4 O2(g) Which of the following is true regarding the reaction represented above? A The oxidation number of O does not change. B The oxidation number of H changes from -1 to +1. C The oxidation number of F changes from +1 to -1. D The oxidation number of Se changes from -2 to +6. E It is a disproportionation reaction for F.

D

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? A HCl(aq) and Cl−(aq) B HCl(aq) and H3O+(aq) C H2O(l)and H3O+(aq) D H2O(l) and Cl−(aq)

D

I2(aq)+C6H8O6(aq)→C6H6O6(aq)+2I−(aq)+2H+(aq) The compound C6H8O6 reacts with I2 according to the reaction represented by the equation above. The reaction is correctly classified as which of the following types? A Acid-base, because H+ ions are produced. B Precipitation, because there are only two reactants but there are three products. C Double replacement, because both H and I appear as ions in the products. D Oxidation-reduction, because I2 is reduced.

D

. . . 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 A: 6 B: 7 C: 12 D: 14 E: 28

C

5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) Which of the following best describes what happens to the pH of the H2O2 solution as the titration proceeds? A The +2 charge on the manganese ions maintains the acidity of the solution. B The production of water dilutes the solution, making it basic. C As H+ ions are consumed, the solution becomes less acidic and the pH increases. D As H+ ions are consumed, the solution becomes less acidic and the pH decreases.

C

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid? A NaF(aq)+HCl(aq)→NaCl(aq)+HF(aq)NaF(aq)+HCl(aq)→NaCl(aq)+HF(aq) B Na+(aq)+F−(aq)+H+(aq)+Cl−(aq)→Na+(aq)+Cl−(aq)+HF(aq)Na+(aq)+F−(aq)+H+(aq)+Cl−(aq)→Na+(aq)+Cl−(aq)+HF(aq) C Na+(aq)+Cl−(aq)→NaCl(aq)Na+(aq)+Cl−(aq)→NaCl(aq) D F−(aq)+H+(aq)→HF(aq)

D

Which of the following represents a process in which a species is reduced? A Ca(s) → Ca2+(aq) B Hg(l) → Hg22+(aq) C Fe2+(aq) → Fe3+(aq) D NO3-(aq) → NO(g) E SO32-(aq) → SO42-(aq)

D

An oxidation-reduction reaction that is also a synthesis reaction A 2 Mg(s) + O2(g) → 2 MgO(s) B Pb2+(aq) + CrO42-(aq) → PbCrO4(s) C SO3(g) + 2 H2O(l) → H3O+(aq) + HSO4-(aq) D 2 H2O(g) → 2 H2(g) + O2(g) E Ag+(aq) + 2 NH3(aq) → [Ag(NH3)2]+(aq)

A

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? A The resulting solution is colorless. B The temperature of the reaction mixture increases. C The total volume of the mixture is approximately equal to the sum of the initial volumes. D The resulting solution conducts electricity.

b

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

c

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 after stirring. B The KClKCl crystals are no longer visible after mixing with water. C There is a temperature change in the solution during the dissolving process. D After the water has evaporated, the white crystals in the beaker have a mass of 20.0g20.0g.

d

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. B When two liquids at room temperature were combined in a beaker, the beaker became hot. C When two clear liquids were combined, the resulting mixture was cloudy. D When a colorless liquid was added to a blue liquid, the resulting solution was yellow.

A

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) B K+(aq)+NO3−(aq)→KNO3(aq) C Pb2+(aq)+2NO3−(aq)+2K+(aq)+2Br−(aq)→2K+(aq)+2NO3−(aq)+PbBr2(s) D Pb(NO3)2(aq)+2KBr(aq)→PbBr2(s)+2KNO3(aq)

A

If 0.40 mol of H2 and 0.15 mol of O2 were to react as completely as possible to produce H2O, what mass of reactant would remain? A 0.20 g of H2 B 0.40 g of H2 C 3.2 g of O2 D 4.0 g of O2 E 4.4 g of O2

A

If equal masses of the following compounds undergo complete combustion, which will yield the greatest mass of CO2? A Benzene, C6H6 B Cyclohexane, C6H12 C Glucose, C6H12O6 D Methane, CH4

A

Potassium hydrogen phthalate, KHP, is used as a primary standard for determining the concentration of a solution of NaOH by titration. If the KHP has not been dried before weighing, the calculated molarity of the NaOH would be A higher than the actual value, since water is included in the apparent mass of KHP B higher than the actual value, since the presence of water requires a larger volume of titrant C lower than the actual value, since NaOH absorbs water D unaffected, since KHP is a strong acid E unaffected, since water is routinely added before the titration

A

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? A: 1 B: 2 C: 3 D: 4

B

H2C2O4(aq) + H2O(l) ⇄ H3O+(aq) + HC2O4-(aq) HC2O4-(aq) + H2O(l) ⇄ H3O+(aq) + C2O42-(aq) H2O(l) + H2O(l) ⇄ H3O+(aq) + OH- (aq) All the reactions represented above occur in an aqueous solution of oxalic acid. Which of the following represent a Brønsted-Lowry conjugate acid-base pair? A H2C2O4(aq) and C2O42-(aq) B HC2O4−(aq) and C2O42-(aq) C HC2O4-(aq) and H2O(aq) D H3O+(aq) and OH−(aq)

B

NH3(aq) + HCl(aq) ⇄ NH4+(aq) + Cl-(aq) The Brønsted-Lowry bases in the reaction represented above are A NH3(aq) and NH4+(aq) B NH3(aq) and Cl-(aq) C NH3(aq) and HCl(aq) D HCl(aq) and NH4+(aq) E HCl(aq) and Cl-(aq)

B

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? A NH4+(aq) acts as a Brønsted-Lowry base. B NH4+(aq) is a stronger acid than H2O(l) is. C NH3(aq) is a stronger base than OH−(aq) is. D NH4+(aq) and Cl−(aq)are a conjugate acid-base pair.

B

Refer to the following types of chemical or physical changes. (A) Oxidation-reduction reaction(B) Brønsted-Lowry acid-base reaction(C) Sublimation(D) Dehydration(E) Precipitation Occurs when aqueous solutions of ammonia and vinegar are mixed A Oxidation-reduction reaction B Brønsted-Lowry acid-base reaction C Sublimation D Dehydration E Precipitation

B

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? A Cl−(aq)+K+(aq)→KCl(aq) B Sr2+(aq)+SO42−(aq)→SrSO4(s) C Sr2+(aq)+2Cl−(aq)+SO42−(aq)+2K+(aq)→SrSO4(s)+2Cl−(aq)+2K+(aq) D SrCl2(aq)+K2SO4(aq)→SrSO4(s)+2KCl(aq)

B

What is the maximum number of moles of Al2O3 that can be produced by the reaction of 0.40 mol of Al with 0.40 mol of O2 ? A 0.10 mol B 0.20 mol C 0.27 mol D 0.33 mol E 0.40 mol

B

Which of the following describes the changes in forces of attraction that occur as H2O changes phase from a liquid to a vapor? A H - O bonds break as H - H and O - O bonds form. B Hydrogen bonds between H2O molecules are broken. C Covalent bonds between H2O molecules are broken. D Ionic bonds between H+ ions and OH- ions are broken. E Covalent bonds between H+ ions and H2O molecules become more effective.

B

A student pipetted five 25.00-milliliter samples of hydrochloric acid and transferred each sample to an Erlenmeyer flask, diluted it with distilled water, and added a few drops of phenolphthalein to each. Each sample was then titrated with a sodium hydroxide solution to the appearance of the first permanent faint pink color. The following results were obtained.Volumes of NaOH SolutionFirst Sample.....35.22 mLSecond Sample.....36.14 mLThird Sample.....36.13 mLFourth Sample .....36.15 mLFifth Sample.....36.12 mLWhich of the following is the most probable explanation for the variation in the student's results? A The burette was not rinsed with NaOH solution. B The student misread a 5 for a 6 on the burette when the first sample was titrated. C A different amount of water was added to the first sample. D The pipette was not rinsed with the HCI solution

D

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? A Ag+(aq)+Ni(s)→Ag(s)+Ni2+(aq) B 2Ag+(aq)+Ni(s)→Ag(s)+2Ni2+(aq) C Ag+(aq)+2Ni(s)→Ag(s)+2Ni2+(aq) D 2Ag+(aq)+Ni(s)→2Ag(s)+Ni2+(aq

D

The following questions refer to the reactions represented below. (A) H2SeO4(aq) + 2 Cl-(aq) + 2 H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l)(B) S8(s) + 8 O2(g) → 8 SO2(g)(C) 3 Br2(aq) + 6 OH-(aq) → 5 Br-(aq) + BrO3-(aq) + 3 H2O(l)(D) Ca2+(aq) + SO42-(aq) → CaSO4(s)(E) PtCl4(s) + 2 Cl-(aq) → PtCl62-(aq) A precipitation reaction A H2SeO4(aq) + 2 Cl-(aq) + 2 H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l) B S8(s) + 8 O2(g) → 8 SO2(g) C 3 Br2(aq) + 6 OH-(aq) → 5 Br-(aq) + BrO3-(aq) + 3 H2O(l) D Ca2+(aq) + SO42-(aq) → CaSO4(s) E PtCl4(s) + 2 Cl-(aq) → PtCl62-(aq)

D

When a buret is rinsed before a titration, which of the techniques below is the best procedure? A Rinse the buret one time with some of the titrant solution. B Rinse the buret one time with some of the titrant solution and then dry the buret in an oven. C Rinse the buret two times: once with some of the titrant solution, then once with distilled water. D Rinse the buret two times: each time with some of the titrant solution. E Rinse the buret two times: each time with distilled water.

D