CHEM 124 Ch.21(1-3) Flashcards
Redox reactions, voltaic cells, standard cell and electrode potentials (exam 3+4)
An electrochemical ____ is the primary system for the study of electrochemical reactions
cell
Oxidation involves the ____ of electrons, while reduction involves the ____ of electrons
loss; gain
If the oxidation # of a substance becomes +, that substance has been ____; if the oxidation # of a substance becomes -, that substance has been____.
oxidized; reduced
Match the element with the most common O.N (assuming polar covalent or ionic bond)
a. Na
b. F
c. Ca
d. O
a. +2
b. -2 or -1
c.+1
d. -1
a. Na, c. +1
b. F, d. -1
c. Ca, a. +2
d. O, b. -2 or -1
O.N can be based on group number
After spectator ions are eliminated, which listed species should be used when balancing equation from former redox reaction?
KMnO4 (aq) + Na2C2O4 (aq) + H2SO4 (aq) → MnSO4 (aq) + K2SO4 (aq) + Na2SO4 (aq) + CO2 (g)+ H2O (l)
Multiple Choice:
a. SO42–
b. CO2
c. H2 (g)
d. MnO4– (aq)
e. H+
f. H2O (l)
g. Na2SO4 (aq)
h. K2SO4 (aq)
I. Mn2+ (aq)
j. C2O42–
b., d., e., f., i., and j.
Get rid of spectator ions and dissociate correctly before 1/2 reaction method
The branch of chemistry that deals with the interconversion of electrical and chemical energy is called ____.
electrochemistry
Based on the following reaction, identify ALL the species that should be included in the oxidation 1/2 reaction: Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)
a. Cu(s)
b. Cu ^2+ (aq)
c. Zn ^ 2+ (aq)
d. Zn(s)
c. and d
If a substance causes another substance to be oxidized then it’s a ____ agent. Likewise the substance that being oxidized in a electrochemical reaction is always the ____ agent.
oxidizing; reducing
Which of the following reactions result in the oxidation of sulfur? Select all that apply.
a. S8 + 8O2 → 8SO2
b. SO2 + H2O2 → H2SO4
c.SO2 + H2O → H2SO3
d. S8 + 8H2 → 8H2S
a and b
Prior to balancing O and H atoms, find missing coefficients from the 1/2 reaction: _NO2^ - -> _NH4^ +
1 and 1
Match the O.N of Cl w/ the appropriate chemical compound
a. NaClO4
b. HCl
c. KClO
d. RbClO3
a. +5
b. -1
c. +1
d. +7
NaClO4-+7
HCl- -1
KClO- +1
RbClO3- +5
Identify the number of water molecules needed to balance the following half-reaction. Also indicate whether the water will appear as a reactant or a product.
MnO4– → MnO2
a. 1H2O; product
b. 1H2O; reactant
c. 2H2O; reactant
d. 2H2O; product
d. 2H2O; product
After spectator ions are eliminated, which of the listed species should be used when balancing the equation for FeCl2 (aq) + NaOH (aq) + H2 (g) → Fe (s) + NaCl (aq) + H2O (l)?
a. H2O (l)
b. H2 (g)
c. OH– (aq)
d. NaOH (aq)
e. NaCl (aq)
f. Fe2+ (aq)
H2O(l), H2(g), OH-(aq), Fe2+ (aq)
For 2Na + 2H2O → 2NaOH + H2, which of the following (unbalanced) reactions should be used as the starting point for the reduction 1/2 reaction?
a. H2O-> H2
b. Na-> H2
c. H20-> NaOH
d. Na-> NaOH
H2O-> H2
When H and O atoms are balanced in the following 1/2 reaction under standard conditions, which of the following statements are correct TiO2 (s) → Ti (s)?
a. 2 mol of H+ as a reactant
b. 4 mols of H+ as a reactant
c. 2 mols of H2O as a product
d. 4 Mols of H2O as a product
4 mols of H+ as a reactant and 2 mols of H2O as a product
Identify the missing coefficient to balance Mn in Mn2O3 → _ MnO2
a. 1/2
b. 2
c. 3
d. 1
2
To which of the following 1/2 reactions must 2 electrons appear as products in order to balance the equation?
a. TiO2 + 4H+ → Ti2+ + 2H2O
b. H2 + 2OH– → 2H2O
c. H2O + PbO → PbO2 + 2H+
d. 2OH– → O2 + 2H+
H2 + 2OH– → 2H2O and H2O + PbO → PbO2 + 2H+.
In which of the following (unbalanced) 1/2 reaction will 1 mol of water appear as a reactant when O atoms are balanced?
a. SO2 → SO42–
Reason: SO2 + 2H2O → SO42–; this half-reaction contains 2 moles of water on the reactant side of the chemical equation.
a. As2O3 → 2AsO43–
b. N2O5 → 2NO3
c. Na → NaOH
d. SO2 → SO42–
N2O5 → 2NO3 and Na → NaOH
Which of the following reactions is Cl reduced?
a. 2LiClO3 + K2Cr2O7 → 2LiClO4 + 2CrO2 + K2O
b. 2NaClO + F2 → NaF + Cl2 + O2
c. Cl2 + 2Na → 2NaCl
d KCl + MnO2 → MnO + KClO
2NaClO + F2 → NaF + Cl2 + O2 and Cl2 + 2Na → 2NaCl
Which of the following are true when the reactions below are added together? Make sure you eliminate that species that appears on both sides of the equation.
Reaction 1: 2BiO+ + 4H+ + 6e– → 2Bi + 2H2O
Reaction 2: 6H2O → 3H2O2 + 6H+ + 6e–
a. 1mol H2O as reactant
b. 4 mol of H2O as a reactant
c. 6 mol of e- appear on each side of the equation
d. 2 mol of H+ appear as product
4 mol of H2O as a reactant and 2 mol of H+ appear as product
When H atoms are balanced in 2ClO3– → Cl2 + 6H2O, identify the amount of the substance that must be introduced, and where it will appear in the equation (the reaction is acidic).
a. 6 H2 as a reactant
b. 6 H2O as a reactant
c. 6 H+ as a reactant
d. 12 H+ as a reactant
12 H+ as a reactant
Which of the following species can be added to balance the H+ ions in a redox reaction occurring in basic medium?
a. OH-
b. H3O+
c. H+
d. H2O
OH-
Identify the # of e- required to balance the following 1/2 reaction. Also indicate whether theses e- must be reactants or products.
a. 1e-; product
b. 2e-; product
c. 1e-; reactant
d. 2e-; reactant
1e-; reactant
The reaction MnO2 + 4H+ + Zn → Mn2+ + 2H2O + Zn2+ is basic. Select all options that correctly describe the balanced equation obtained after all resulting species are combined and/or canceled correctly.
a. 4 mol OH- appear among the products
b. 4 mol of OH- reactant
c. 2 mol H2O reactants
d. 2 mol H2O products
4 mol OH- appear among the products and 2 mol H2O reactants
Identify the role played by the individual species in the redox reaction represented by the equation Fe(NO3)2 (s) + Al (s) → Fe (s) + Al(NO3)3 (aq)
Fe2+, Al, Reducing and oxidizing agents, and NO3-
a. species reduced
b. spectator ions
c. Al
d. Fe2+
e. species oxidized
Fe2+: species reduced
Al: species oxidized
Reducing Agents: Al
Oxidizing Agent: Fe 2+
NO-3: Spectator ion