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Regents Chemistry Exam Multiple Choice Practice With Solutions: Oxidation/ Reduction Topic

January 2023

24 In an electrochemical cell, oxidation occurs at the


(1) anode

(2) cathode

(3) salt bridge

(4) switch


Solution: Here is what you need to memorize for the electrochemistry chapter. An Ox ( anode is oxidation) and Red Cat ( reduction occurs at the cathode).

Answer: 1 is the correct answer.


25 Which energy conversion occurs in an operating electrolytic cell?

(1) chemical energy to electrical energy

(2) electrical energy to chemical energy

(3) nuclear energy to electrical energy

(4) electrical energy to nuclear energy


Solution: Electrolytic cell requires an input of energy to operate. It converts electrical energy into chemical energy.

Answer: Choice 2 is the correct answer.


46 Based on Table J, atoms of which metal will lose electrons to Ca2+ ions?

(1) aluminum

(2) lead

(3) nickel

(4) potassium


Solution: On the Activity Series, metal on the top of the table are most active and on the bottom are least active. Metal that will lost electrons to Ca^2+ ions must be higher on the table than calcium. Potassium, K, is higher than calcium and is therefore the correct answer.

Answer:4


August 2022

25. Which reaction occurs at the anode in an electrochemical cell?

(1) neutralization

(2) oxidation

(3) reduction

(4) substitution


Explanation: A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation.

Answer: 2


49 The diagram and ionic equation below represent an operating voltaic cell.

Which phrase describes the direction of electron flow in this cell?

(1) from Ni(s) through the wire to Mg(s)

(2) from Mg(s) through the wire to Ni(s)

(3) from Ni^2+(aq) ions through the salt bridge to Mg^2+(aq) ions

(4) from Mg^2+(aq) ions through the salt bridge to Ni^2+(aq) ions


Explanation: In a voltaic cell, electrons flow from the anode(loss of electrons) to the cathode(gain of electrons) through the wire, not salt bridge. This eliminates choices 3 and 4. The anode is usually on the left in the diagram and cathode on the right, making choice 2 the correct answer

Answer: 2


June 2022


26 Which reaction occurs at the anode in an electrochemical cell? (1) saponification

(2) oxidation (3) esterification

(4) reduction


Solution: A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation.

Answer:2


27 Which statement describes the two types of reactions that occur in operating electrochemical cells?

(1) Nonspontaneous reactions occur in voltaic cells, and spontaneous reactions occur in electrolytic cells.

(2) Nonspontaneous reactions occur in electrolytic cells, and nonspontaneous reactions occur in voltaic cells.

(3) Spontaneous reactions occur in voltaic cells, and nonspontaneous reactions occur in electrolytic cells.

(4) Spontaneous reactions occur in electrolytic cells, and spontaneous reactions occur in voltaic cells.


Solution: A voltaic cell has spontaneous reactions, while an electrochemical cell has nonspontaneous reactions.

Answer: 3


January 2020


21 Which particles are transferred during a redox reaction?

(1) atoms

(2) electrons (3) neutrons

(4) positrons


Solution: Electrons are transferred during a redox reaction.

Answer: 2


22 Which process can be represented by a half- reaction equation?

(1) distillation

(2) oxidation

(3) sublimation

(4) vaporization


Solution: Half reaction refers to either oxidation or reduction.

Answer: 2


23 Which form of energy is converted to electrical energy in a voltaic cell?

(1) chemical

(2) mechanical

(3) nuclear

(4) thermal


Solution: In a voltaic cell, chemical energy is converted into electrical energy.

Answer: 1


45 When comparing voltaic cells to electrolytic cells, oxidation occurs at the (1) anode in both types of cells

(2) cathode in both types of cells

(3) anode in voltaic cells, only

(4) cathode in voltaic cells, only

Solution: For both voltaic and electrolytic cells, oxidation occurs at the anode. A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation.

Answer: 1


46 Based on Table J, which metal is more active than tin, but less active than zinc? (1) Ag

(2) Cr

(3) Cs

(4) Mn


Solution: On Table J on the Reference Table, metals on the top of the table are most active and on the bottom are least active. We are looking for a metal that is higher than tin but lower than zinc.

Answer: 2


August 2019


25 Which statement describes the reactions in an electrochemical cell? (1) Oxidation occurs at the anode, and reduction occurs at the cathode. (2) Oxidation occurs at the cathode, and reduction occurs at the anode. (3) Oxidation and reduction both occur at the cathode.

(4) Oxidation and reduction both occur at the anode.


Solution: A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation.

Answer: 1


46 Given the equation representing a reaction: 2Ca(s) + O2(g) → 2CaO(s) During this reaction, each element changes in (1) atomic number (2) oxidation number (3) number of protons per atom

(4) number of neutrons per atom


Solution: This is a redox reaction since Ca has an oxidation number of 0 as a reactant and +2 as a product. Similarly, oxygen goes from 0 to -2. Each elements changes in oxidation number.

Answer: 2


June 2019


48 Given the equation representing a reaction:

3CuCl2(aq) + 2Al(s) → 3Cu(s) + 2AlCl3(aq) The oxidation number of copper changes from

(1) +1 to 0

(2) +2 to 0

(3) +2 to +1

(4) +6 to +3


Solution: Let's calculate the oxidation number of copper in CuCl2. Cl has an oxidation number if -1 according to the Periodic Table. The molecule is neutral overall. We can make an equation where x is the oxidation number of copper.

X + 2(-1) = 0

X = +2

An element on its own has an oxidation number of 0. Therefore Cu(s) is 0.

Answer: Choice 2


January 2019


25 Which metal is most easily oxidized? (1) Ag

(2) Co

(3) Cu

(4) Mg


Solution: On Table J on the Reference Table, metals on the top of the table are most active and on the bottom are least active. Most active metals are most easily oxidized.

Answer: 4



45 Which half-reaction equation represents reduction? (1) Cu → Cu^2+ + 2e-

(2) Cu^2+ + 2e- → Cu

(3) Ag + e- →Ag+

(4) Ag+ →Ag + e-


Solution: We can remember the mnemonic OIL RIG. OIL (oxidation is loss of electrons). RIG (reduction is gain of electrons). For this question, we are looking for reduction; gain of electrons. Gaining electrons means we would see them on the reactant side, eliminating choices 1 and 4. Next, we can see if the charges on both side of the equation are equal. For choice 2, the total charge on the left of the arrow is 0 (+2-2=0). The charge on the right of the equation is zero as well. For choice 3, the charge on the left is -1 while the charge on the right is +1, eliminating choice 3.

Answer: 2



46 Given the balanced ionic equation representing a reaction: Zn(s) + Co^2+(aq) → Zn^2+(aq) + Co(s) Which statement describes the electrons involved in this reaction?

(1) Each Zn atom loses 2 electrons, and each Co2+ ion gains 2 electrons.

(2) Each Zn atom loses 2 electrons, and each Co2+ ion loses 2 electrons.

(3) Each Zn atom gains 2 electrons, and each Co2+ ion loses 2 electrons.

(4) Each Zn atom gains 2 electrons, and each Co2+ ion gains 2 electrons.


Solution: Zn has the oxidation number of 0 (all free, neutral elements have an oxidation number of zero) to the left of the arrow. It has the oxidation number of 2+ to the right of the arrow. Let's remember that electrons are negative. Going from 0 to +2 means 2 electrons are lost, eliminating choices 3 and 4. Copper goes from +2 charge to 0, which means it is gaining 2 electrons.

Answer: 1


47 What are the two oxidation states of nitrogen in NH4NO2?

(1) +3 and +5

(2) +3 and -5 (3) -3 and +3

(4) -3 and -3


Solution: To find oxidation states, let's first look at some rules for oxidation numbers.

Oxygen is usually -2 unless in peroxides

Hydrogen is +1 unless it is bonded to a metal

The sum of oxidation numbers in a polyatomic ions is equal to the charge of the polyatomic ion.

The compound present is composed of two polyatomic ions: NH4+ and NO2-

NH4+

x+(+1*4)=+1

x= -3

NO2-

x+(-2*2)=-1

x=+3

Answer: 3



August 2018


25 Which value changes when a Cu atom becomes a Cu^2+ ion? (1) mass number (2) oxidation number

(3) number of protons

(4) number of neutrons


Solution: All free, neutral elements have an oxidation number of zero. Cu atom has an oxidation number of zero while Cu^2+ ion has an oxidation number of 2+

Answer:2


26 Which reaction occurs at the anode in an electrochemical cell? (1) oxidation

(2) reduction

(3) combustion

(4) substitution


Solution: A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation.

Answer: 1


46 Given the equation representing a reaction: Cd+NiO2+2H2O→Cd(OH)2 + Ni(OH)2 Which half-reaction equation represents the oxidation in the reaction?









Solution: We can remember the mnemonic OIL RIG. OIL (oxidation is loss of electrons). RIG (reduction is gain of electrons). For this question, we are looking for an oxidation half reaction. Oxidation means electrons are lost and we should see them on the right side of the equation, eliminating choices 1 and 4. Furthermore, the charge on both sides of the equation needs to be the same. For choice 2 the charge on the left is 4+ and on the right is 0 (+2-2=0). This eliminates choice 2. In choice 3, the charge on the left is 0 and the charge on the right is 0 (+2-2=0).

Answer: 3


January 2018


22 Which change occurs at the anode in an operating electrochemical cell? (1) gain of protons

(2) gain of electrons

(3) loss of protons

(4) loss of electrons


Solution: A good mnemonic to memorize for the electrochemistry chapter is : Red Cat and An Ox. Red Cat stands for reduction is at the cathode. An Ox stands for anode is oxidation. Next, we can remember the mnemonic OIL RIG. OIL (oxidation is loss of electrons). RIG (reduction is gain of electrons).

Answer: 4


23 Which device requires electrical energy to produce a chemical change? (1) electrolytic cell

(2) salt bridge

(3) voltaic cell

(4) voltmeter


Solution: An electrolytic cells requires electrical energy to produce a chemical change.

Answer: 1



June 2018


23 Which energy conversion occurs in an operating voltaic cell? (1) chemical energy to electrical energy

(2) chemical energy to nuclear energy

(3) electrical energy to chemical energy

(4) electrical energy to nuclear energy


Solution: Voltaic cell generates energy spontaneously. It converts chemical energy into electrical energy.

Answer: 1


24 Which process requires energy to decompose a substance?

(1) electrolysis

(2) neutralization (3) sublimation

(4) synthesis


Solution: Electrolysis requires energy to decompose a substance. Neutralization is a reaction between an acid and a base. Sublimation is conversion of a solid substance into gas. Synthesis is a reaction where several substances react together to produce one substance.

Answer: 1


46 Given the balanced equation representing a reaction: Ni(s) + 2HCl(aq) → NiCl2(aq) + H2(g) In this reaction, each Ni atom (1) loses 1 electron

(2) loses 2 electrons

(3) gains 1 electron

(4) gains 2 electrons

Solution: Let's look at the oxidation numbers of nickel to the left of the arrow and the right. Free, neutral elements have an oxidation number of 0. Therefore Ni(s) has an oxidation number of 0. Next, we can calculate the oxidation number of Ni in NiCl2. The oxidation number of Cl is -1 according to the Periodic Table. The overall charge of the molecule is 0 since it is neutral.

x+(-1*2)=0

x= +2

Therefore, nickel goes from 0 on the reactant side to +2 on the product side. Remember that electrons are negative. It must be loses 2 electrons.

Answer: 2


47 Which equation represents a reduction half- reaction?

(1) Fe→Fe^3+ + 3e–

(2) Fe+3e- →Fe^3+ (3) Fe^3+ →Fe+3e–

(4) Fe^3+ + 3e- →Fe


Solution: We can remember the mnemonic OIL RIG. OIL (oxidation is loss of electrons). RIG (reduction is gain of electrons). For the reduction half-reaction, we expect to see electrons on the left side of the equation, eliminating choices 1 and 3. Furthermore, the charge on both sides of the equation must be equal. For 2, the charge on the left (reactant side) is 3- and the charge on the right (product side) is 3+. In choice 4, the charge on both sides is 0.

Answer: 4


48 Given the balanced ionic equation representing a reaction: Cu(s) + 2Ag+(aq) → Cu^2+(aq) + 2Ag(s) During this reaction, electrons are transferred from (1) Cu(s) to Ag+(aq)

(2) Cu^2+(aq) to Ag(s)

(3) Ag(s) to Cu^2+(aq)

(4) Ag+(aq) to Cu(s)

Solution: According to the reaction, Cu becomes Cu^2+ which means it loses 2 electrons. Ag+ becomes Ag which means it gains an electron. The electrons must be traveling from Cu to Ag+

Answer: 1


49 Which metal reacts spontaneously with Sr2+ions?

(1) Ca(s) (2) Co(s)

(3) Cs(s)

(4) Cu(s)


Solution: We need to look at Table J on the Periodic Table. The metal that reacts spontaneously with Sr2+ions must be higher on the table (more active) than Sr.

Answer: 3


June 2017


28 During an oxidation-reduction reaction, the number of electrons gained is (1) equal to the number of electrons lost

(2) equal to the number of protons gained

(3) less than the number of electrons lost

(4) less than the number of protons gained


Solution: During an oxidation-reduction reaction, the number of electrons gained is equal to the number of electrons lost to make sure the charge is preserved.

Answer:1


29 Which process requires energy for a nonspontaneous redox reaction to occur? (1) deposition (2) electrolysis

(4) chromatography

(3) alpha decay


Solution: Electrolysis requires energy for a nonspontaneous redox reaction to occur. Alpha decay is a nuclear reaction that produces an alpha particle. Deposition is conversion of gaseous substance into solid. Chromatography is a laboratory technique that separates substances based on their polarity.

Answer: 2



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