6. Chemical Quantities & Aqueous Reactions

Phosphoric acid H₃PO₄ has many industrial uses and is often found in some cola drinks. If you had 25.0 mL of a 0.200 M solution of H₃PO₄, how many mL of a 0.400 M solution of Ba(OH)₂ would be required to neutralize the acid according to the following reaction? ?

2 H₃PO₄ (aq) + 3 Ba(OH)₂ (aq) → Ba₃(PO₄)₂ (s) + 6 H₂O (l)

A 10.00-mL sample of a 0.130 M H₃PO₄ solution is added to 13.00 mL of a 0.150 M Ba(OH)₂ solution. When the reaction is complete, what spectator ions are present?

2 H₃PO₄ (aq) + 3 Ba(OH)₂ (aq) → Ba₃(PO₄)₂ (s) + 6 H₂O (l)

A 25.00-mL sample of H₂SO₄ solution of unknown concentration requires 28.27 mL of a 0.185 M KOH solution to complete the neutralization reaction. What is the concentration of the unknown H₂SO₄ solution?

Which of the following unbalanced half-reactions is correctly labeled as an oxidation or reduction? (a) NO3- (aq) -> NO(g); reduction (b) Zn(s) -> Zn2+(aq); reduction (c) ClO3-(aq) -> Cl2(g); oxidation (d) Br-(aq) -> Br2(l); reduction

What is the coefficient on Sn2_ when the following reaction is balanced in acidic solution? (a) 2 (b) 4 (c) 5 (d) 7

Complete and balance the following half-reactions. In each case, indicate whether the half-reaction is an oxidation or a reduction. (b) TiO21s2 ¡ Ti2+1aq2 (acidic solution)

Complete and balance the following half-reactions. In each case indicate whether the half-reaction is an oxidation or a reduction. (b) H2SO31aq2 ¡ SO42-1aq2 (acidic solution)

Complete and balance the following equations, and identify the oxidizing and reducing agents: (d) As2O31s2 + NO3-1aq2 ¡ H3AsO41aq2 + N2O31aq2 (acidic solution)

Complete and balance the following equations, and identify the oxidizing and reducing agents: (a) Cr2O72-1aq2 + I-1aq2 ¡ Cr3+1aq2 + IO3-1aq2 (acidic solution)

Complete and balance the following equations, and identify the oxidizing and reducing agents. (Recall that the O atoms in hydrogen peroxide, H2O2, have an atypical oxidation state.) (c) Cr2O72 - 1aq2 + CH3OH1aq2 ¡ HCOOH1aq2 + Cr3+1aq2 (acidic solution)

Balance each redox reaction occurring in acidic aqueous solution. c. BrO3-(aq) + N2H4(g) ¡ Br-(aq) + N2(g)

Balance each redox reaction occurring in acidic aqueous solution. a. K(s) + Cr3+(aq) ¡ Cr(s) + K+(aq)

Balance each redox reaction occurring in acidic aqueous solution. c. MnO4-(aq) + Al(s) ¡ Mn2+(aq) + Al3+(aq)

Balance each redox reaction occurring in acidic aqueous solution. a. Zn(s) + Sn2+(aq) ¡ Zn2+(aq) + Sn(s)

Balance each redox reaction occurring in acidic aqueous solution. b. Mg(s) + Cr3+(aq) ¡ Mg2+(aq) + Cr(s)

Balance each redox reaction occurring in acidic aqueous solution. a. I-(aq) + NO2-(aq) ¡ I2(s) + NO(g)

Balance each redox reaction occurring in acidic aqueous solution. c. NO3-(aq) + Sn2+(aq) ¡ Sn4+(aq) + NO(g)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (d) SbCl4-(aq) -> SbCl6-(aq)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (b) Pt2+ (aq) -> Pt(s)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (a) HLCO(aq) -> Cl2(g)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (c) Cr(s) -> Cr3+ (aq)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (d) CH3OH(aq) -> CH2O(aq)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (b) H2O2(aq) -> O2(g)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (a) O2(g) -> OH-(aq)

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (c) MnO4-(aq) -> MnO42-(aq)

Balance the half-reactions in Problem 19.42, assuming that they occur in acidic solution.

Write unbalanced oxidation and reduction half-reactions for the following processes. . (b) H2O2(aq) + Fe2+(aq) -> Fe3+(aq) + H2O(l)

Write unbalanced oxidation and reduction half-reactions for the following processes. . (a) Te(s) + NO3-(aq) -> TeO2(s) + NO(g)

Write unbalanced oxidation and reduction half-reactions for the following processes. . (b) Mn3+(aq) -> MnO2(s) + Mn2+(aq)

Write unbalanced oxidation and reduction half-reactions for the following processes. . (a) Mn(s) + NO3-(aq) -> Mn2+(aq) + NO2(g)

Write balanced net ionic equations for the following reactions in acidic solution. (c)

Write balanced net ionic equations for the following reactions in acidic solution. (b)

Write balanced net ionic equations for the following reactions in acidic solution. (a)

Write balanced net ionic equations for the following reactions in acidic solution. (c)

Write balanced net ionic equations for the following reactions in acidic solution. (b)

Write balanced net ionic equations for the following reactions in acidic solution. (a)

Given the following reduction half-reactions: Fe3+1aq2 + e- ¡ Fe2+1aq2 E°red = +0.77 V S2O62 - 1aq2 + 4 H+1aq2 + 2 e- ¡ 2 H2SO31aq2 E°red = +0.60 V N2O1g2 + 2 H+1aq2 + 2 e- ¡ N21g2 + H2O1l2 Ered ° = -1.77 V VO2+1aq2 + 2 H+1aq2 + e- ¡ VO2+ + H2O1l2 E°red = +1.00 V (a) Write balanced chemical equations for the oxidation of Fe2+1aq2 by S2O62-1aq2, by N2O1aq2, and by VO2+1aq2.

A galvanic cell is constructed from a Zn/Zn2+ half-cell (anode) and a Cl2/Cl- half-cell (cathode). (b) Write balanced equations for the electrode and overall cell reactions.

A disproportionation reaction is an oxidation–reduction reaction in which the same substance is oxidized and reduced. Complete and balance the following disproportionation reactions: (b) MnO42-1aq2 ¡ MnO4-1aq2 + MnO21s2 (acidic solution)

Consider the unbalanced redox reaction: Cr2O72-(aq) + Cu(s) ¡ Cr3+(aq) + Cu2+(aq) Balance the equation and determine the volume of a 0.850 M K2Cr2O7 solution required to completely react with 5.25 g of Cu.

The discovery of hafnium, element number 72, provided a controversial episode in chemistry. G. Urbain, a French chemist, claimed in 1911 to have isolated an element number 72 from a sample of rare earth (elements 58–71) compounds. However, Niels Bohr believed that hafnium was more likely to be found along with zirconium than with the rare earths. D. Coster and G. von Hevesy, working in Bohr's laboratory in Copenhagen, showed in 1922 that element 72 was present in a sample of Norwegian zircon, an ore of zirconium. (The name hafnium comes from the Latin name for Copenhagen, Hafnia). (c) Solid zirconium dioxide, ZrO2, reacts with chlorine gas in the presence of carbon. The products of the reaction are ZrCl4 and two gases, CO2 and CO in the ratio 1:2. Write a balanced chemical equation for the reaction.

Consider the following unbalanced oxidation-reduction reactions in aqueous solution: Ag+1aq2 + Li1s2¡ Ag1s2 + Li+1aq2 Fe1s2 + Na+1aq2¡ Fe2 + 1aq2 + Na1s2 K1s2 + H2O1l2¡ KOH1aq2 + H21g2 (a) Balance third reaction.

Consider the following unbalanced oxidation-reduction reactions in aqueous solution: Ag+1aq2 + Li1s2¡ Ag1s2 + Li+1aq2 Fe1s2 + Na+1aq2¡ Fe2 + 1aq2 + Na1s2 K1s2 + H2O1l2¡ KOH1aq2 + H21g2 (a) Balance second reaction.

Zinc is attached to a ship's steel propeller to prevent the steel from rusting. Write balanced equations for the corro-sion reactions that occur (a) in the presence of Zn and (b) in the absence of Zn.

Chlorine can be prepared in the laboratory by the reaction of hydrochloric acid and potassium permanganate. (a) Use data in Appendix D to write a balanced equation for the reaction. The reduction product is Mn2+.

(b) Calculate the concentrations of all ions in the solution after reaction. Check your concentrations to make sure that the solution is electrically neutral.

Given the following standard reduction potentials at 25 °C, (a) balance the equation for the reaction of H2MoO4 with elemental arsenic in acidic solution to give Mo3+ and H3AsO4 and (b) calculate E° for this reaction.

To 100.0 mL of a solution that contains 0.120 M Cr(NO3)2 and 0.500 M HNO3 is added to 20.0 mL of 0.250 M K2Cr2O7. The dichromate and chromium(II) ions react to give chromium(III) ions. (a) Write a balanced net ionic equation for the reaction.

Sodium nitrite, NaNO2, is frequently added to processed meats as a preservative. The amount of nitrite ion in a sample can be determined by acidifying to form nitrous acid (HNO2), letting the nitrous acid react with an excess of iodide ion, and then titrating the I3 - ion that results with thiosulfate solution in the presence of a starch indicator. The unbalanced equations are (1) (2) (b) When a nitrite-containing sample with a mass of 2.935 g was analyzed, 18.77 mL of 0.1500 M Na2S2O3 solution was needed for the reaction. What is the mass percent of NO2- ion in the sample?

Sodium nitrite, NaNO2, is frequently added to processed meats as a preservative. The amount of nitrite ion in a sample can be determined by acidifying to form nitrous acid (HNO2), letting the nitrous acid react with an excess of iodide ion, and then titrating the I3 - ion that results with thiosulfate solution in the presence of a starch indicator. The unbalanced equations are (1) (2) (a) Balance the two redox equations.

(c) The brass sample in part (b) yielded 0.246 g of Zn2P2O7. What is the mass percent zinc in the brass?

(b) When a brass sample with a mass of 0.544 g was sub-jected to the preceding analysis, 10.82 mL of 0.1220 M sodium thiosulfate was required for the reaction with iodine. What is the mass percent copper in the brass?

Brass is an approximately 4:1 alloy of copper and zinc, along with small amounts of tin, lead, and iron. The mass per-cents of copper and zinc can be determined by a procedure that begins with dissolving the brass in hot nitric acid. The resulting solution of Cu2+ and Zn2+ ions is then treated with aqueous ammonia to lower its acidity, followed by addi-tion of sodium thiocyanate (NaSCN) and sulfurous acid (H2SO3) to precipitate copper(I) thiocyanate (CuSCN). The solid CuSCN is collected, dissolved in aqueous acid, and treated with potassium iodate (KIO3) to give iodine, which is then titrated with aqueous sodium thiosulfate (Na2S2O3). The filtrate remaining after CuSCN has been removed is neutralized by addition of aqueous ammonia, and a solu-tion of diammonium hydrogen phosphate ((NH4)2HPO4) is added to yield a precipitate of zinc ammonium phosphate (ZnNH4PO4). Heating the precipitate to 900 °C converts it to zinc pyrophosphate (Zn2P2O7), which is weighed. The equations are (1) (2) (3) (4) (5) (a) Balance all equations.

(d) Balance all equations.

On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac- tion. The unbalanced equation is X (b) How many moles of oxide were formed, and how many moles of semimetal were in the initial 0.200 g sample?

On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac-tion. The unbalanced equation is (a) Balance the equation.

(c) What is the identity of the semimetal M?

Complete and balance the following half-reaction in acidic solution