HW Redox

What is the oxidation state of nitrogen in the compound NH4Br? A. -1 B. +2 C. +4 D. -3

-3

Given the reaction that occurs in an electrochemical cell: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) During this reaction, the oxidation number of Zn changes from 1) +2 to 0 2) 0 to -2 3) -2 to 0 4) 0 to +2

0 to +2

Which expression correctly represents a balanced reduction half-reaction? a.) Na1+ + e- -> Na b.) Na -> Na1+ + e- c.) Cl2 + 2e- -> Cl- d.) 2Cl1- -> Cl2 + 2e-

Na1+ + e- -> Na

When a voltaic cell operates, ions move through the (1) anode (2) cathode (3) salt bridge (4) external circuit

salt bridge

What is the oxidation number of sulfur in Na2S2O3? (1) -1 (3) +6 (2) +2 (4) +4

+2

What is the oxidation state of nitrogen in NaNO2? (1) +1 (3) +3 (2) +2 (4) +4

+3

Given the balanced equation representing a reaction: Fe2o3 + 2Al -> Al2O3 + 2Fe During this reaction, the oxidation number of Fe changes from a.) +2 to 0 as electrons are transferred b.) +2 to 0 as protons are transferred c.) +3 to 0 as electrons are transferred d.) +3 to 0 as protons are transferred

+3 to 0 as electrons are transferred

Given the balanced equation representing a reaction: 2KClO3(s) 2KCl(s) + 3O2(g) The oxidation state of chlorine in this reaction changes from (1) -1 to +1 (2) -1 to +5 (3) +1 to -1 (4) +5 to -1

+5 to -1

What is the oxidation number of chromium in the chromate ion, CrO42-? (1) +6 (3) +3 (2) +2 (4) +8

+6

What is the oxidation number assigned to manganese in KMnO4? (1) +7 (3) +3 (2) +2 (4) +4

+7

What is the oxidation number of iodine in KIO4? (1) +1 (2) -1 (3) +7 (4) - 7

+7

Given the reaction for the corrosion of aluminum: 4 Al + 3 O2 → 2 Al2O3 Which half-reaction correctly represents the oxidation that occurs? 1) Al + 3e- → Al3+ 2) Al → Al3+ + 3e- 3) O2+ 4e- → 2 O2- 4) O2 → 2 O2- + 4e-

Al → Al3+ + 3e-

When an equation is correctly balanced, it must show conservation of A. charge but not of mass B. neither charge nor mass C. both charge and mass D. Mass but not of charge

Both charge and mass

Which process occurs in an operating voltaic cell? (1) Electrical energy is converted to chemical energy. (2) Chemical energy is converted to electrical energy. (3) Oxidation takes place at the cathode. (4) Reduction takes place at the anode.

Chemical energy is converted to electrical energy.

Which half-reaction shows conservation of charge? a.) Cu + e- -> Cu+ b.) Cu2+ +2e- -> Cu c.) Cu1+ -> Cu + e- d.) Cu2+ -> Cu + 2e-

Cu2+ + 2e- -> Cu

In which substance does hydrogen have an oxidation number of zero 1. LiH 3. H2S 2. H2O 4. H2

H2

In which substance does chlorine have an oxidation number of +1? (1) Cl2 (2) HCl (3) HClO (4) HClO2

HClO

What is the purpose of the salt bridge in a voltaic cell? (1) It blocks the flow of electrons (2) It blocks the flow of positive and negative ions. (3) It is a path for the flow of electrons. (4) It is a path for the flow of positive and negative ions.

It is a path for the flow of positive and negative ions

Which half-reaction correctly represents reduction? 1) S2- + 2e- → S0 2) S2-→ S0+ 2e- 3) Mn7+ + 3e- → Mn4+ 4) Mn7+ → Mn4+ + 3e-

Mn7+ + 3e- → Mn4+

Which statement describes where the oxidation and reduction half-reactions occur in an operating electrochemical cell? a.) Oxidation and reduction both occur at the anode. b.) Oxidation and reduction both occur at the cathode c.) Oxidation occurs at the anode, and reduction occurs at the cathode d.) Oxidation occurs at the cathode, and reduction occurs at the anode. c.) oxidation occurs at the anode, and reduction occurs at the cathode

Oxidation occurs at the anode, and reduction occurs at the cathode

Which half-reaction can occur at the anode in a voltaic cell? A. Ni2+ + 2e - >> Ni B. Sn + 2e- >>Sn2+ C. Zn >> Zn2+ + 2e - D. Fe3+ >> Fe 2+ + e -

Zn >>Zn2+ + 2e -

A student collects the materials and equipment below to construct a voltaic cell. • two 250-mL beakers • wire and a switch • one strip of magnesium • one strip of copper • 125 mL of 0.20 M Mg(NO3)2(aq) • 125 mL of 0.20 M Cu(NO3)2(aq) Which additional item is required for the construction of the voltaic cell? (1) an anode (3) a cathode (2) a battery (4) a salt bridge

a salt bridge

Which half-reaction equation represents the reduction of a potassium ion? a.) K 1+ + e- -> K b.) K + e- c.) K 1+ -> K + e- d.) K -> K 1+ + e-

a.) K 1+ + e- -> K

During the operation of a voltaic cell, the cell produces 1) electrical energy spontaneously 2) chemical energy spontaneously 3) electrical energy nonspontaneously 4) chemical energy nonspontaneously

electrical energy spontaneously

Given the redox reaction: Cr3+ + Al-->Cr + Al3+ As the reaction takes place, there is a transfer of (1) electrons from Al to Cr3+ (2) electrons from Cr3+ to Al (3) protons from Al to Cr3+ (4) protons from Cr3+ to Al

electrons from Al to Cr3+