6. Chemical Quantities & Aqueous Reactions

Balancing Redox Reactions: Acidic Solutions

How To Balance Redox Reactions in Acidic Solution! (Half Reaction Method)

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

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.

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.

What is the coefficient of Fe3+ when the following reaction is balanced?Bi3+ (aq) + Fe3+ (aq) + H2O (l) → BiO3-&nbsp;(aq) + Fe2+ (aq) + H+ (aq)

Balance the half-reactions in Problem 19.42, assuming that they occur in acidic solution. <QUESTION REFERENCES PROBLEM 19.42>

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

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

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

Balancing Redox Reactions in Acidic and Basic Conditions

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)

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

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

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

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.

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

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)

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

The reaction stoichiometry is 2 KOH : 1 H2SO4.

 Correct, based on the reaction stoichiometry. 

The volume of KOH must be used with 0.185 M to find moles of KOH used in the reaction.

The volumes used for each reactant are different and the reaction stoichiometry is 2 KOH : 1 H2SO4.

 This is the number of moles of KOH used in the reaction. 

This is the number of moles of H2SO4 used in the reaction.

 Write out a balanced stoichiometric equation. 

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?

Balance the following redox reaction in an acidic solution.Cl2 (g) + S2O32-&nbsp;(aq) → Cl- (aq) + SO42- (aq)

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

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+. <QUESTION REFERS TO APPENDIX D>

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.

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

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

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

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

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

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.

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

 Consider that the reaction ratio between phosphoric acid and barium hydroxide is 2:3, respectively. 

 Correct on all aspects of the calculation. 

 The reaction ratio between phosphoric acid and barium hydroxide is 2:3, respectively. 

 Use molarity as a conversion factor between volume and moles. 

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) &#8594; Ba3(PO4)2 (s) + 6 H2O (l)

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

Acidic Redox Reactions&nbsp;generally have the presence of an H+ ion.&nbsp;

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.

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

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

Balance Redox Reaction: Acidic Solution (Example)

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.

Balancing Redox Reactions (Acidic Conditions)

Chemistry 13.6b More Balancing by Half-Reactions (Acidic)

(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?

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.

Balancing Redox Reactions: Acidic Solutions Example 1

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?

Balancing Redox Reactions: Acidic Solutions Example 2

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

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.

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

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

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.

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) Cr(s) -> Cr3+ (aq)

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 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.

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?

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

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)

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

 The molar quantities of each reactant added produces a reaction in which there is no excess reactant and all of the ions present form either water or the precipitate of barium phosphate. 

 Correct, there is no excess reactant in the quantities used. 

 Use the solubility rules to determine the solubility of the products and reactants. 

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) &#8594; Ba3(PO4)2 (s) + 6 H2O (l)

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.
c. NO3-(aq) + Sn2+(aq) ¡ Sn4+(aq) + NO(g)

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1. Intro to General Chemistry

2. Atoms & Elements

3. Chemical Reactions

4. BONUS: Lab Techniques and Procedures

5. BONUS: Mathematical Operations and Functions

7. Gases

8. Thermochemistry

9. Quantum Mechanics

10. Periodic Properties of the Elements

11. Bonding & Molecular Structure

12. Molecular Shapes & Valence Bond Theory

13. Liquids, Solids & Intermolecular Forces

14. Solutions

15. Chemical Kinetics

16. Chemical Equilibrium

17. Acid and Base Equilibrium

18. Aqueous Equilibrium

19. Chemical Thermodynamics

20. Electrochemistry

21. Nuclear Chemistry

22. Organic Chemistry

23. Chemistry of the Nonmetals

24. Transition Metals and Coordination Compounds

[BOOK CHEM] Clutch Version

Solutions

Solutions represent homogeneous mixtures made of 2 or more components that form a uniform composition.&nbsp;

Osmolarity

Osmolarity (ionic molarity) represents the number of moles of ions per liter of solution.&nbsp;

Gas Evolution Equations

A Gas Evolution Equation is a molecular equation that involves the creation of specific gases.&nbsp;

Molecular Equations

Molecular Equations show reacting molecules involved in a chemical reaction.&nbsp;

Complete Ionic Equations

Complete Ionic Equations show aqueous compounds as fully dissociated ions.&nbsp;

Solubility Rules

The Solubility Rules are a convenient set of guidelines to help us determine if a compound will be soluble or insoluble.

Molarity

Ever wonder how a mass amount such as moles can be converted into the volume amount of liters? Well, molarity serves as the bridge between moles and liters.&nbsp;

Electrolytes

Electrolytes are compounds that can conduct electricity once they are dissolved in a solvent.&nbsp;

Solution Stoichiometry

Solution Stoichiometry deals with stoichiometric calculations in solutions that involve volume and molarity.

Calculate Oxidation Numbers

Calculating Oxidation Numbers is the first pivotal step in understanding redox reactions.&nbsp;

Dilutions

In Dilutions, a solvent (usually water) is added to a concentrated solution.&nbsp;

Redox Reactions

Redox Reactions (oxidation-reduction reactions) involve transference of an electron(s) between reactants.

Activity Series

Activity Series is a list of single displacement reactions in order of reactivity.

Balancing Redox Reactions requires a new approach that accounts for the transfer of electrons between reactants.

Balancing Redox Reactions: Basic Solutions

Balancing Basic Redox Reactions requires all the same steps as balancing in an acidic solution plus an additional step.