Reduction-oxidation (redox) reactions are chemical reactions in which reactants endure a readjust in oxidation number (which means these reactants either acquire or shed electrons).

If an atom in a reactant gained electrons (its oxidation # decreased) it was lessened.

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If an atom in a reactant shed electrons (its oxidation # increased) it was oxidized.

Since chemical reactions do not make or destroy electrons, oxidation and reduction need to happen at the same time. As one reactant is oxidized, the electrons it loses are accepted by an additional reactant which is reduced. Cu2+ + Zn --> Cu + Zn2+ The Cu2+ is diminished (ox. # decreased).

The Zn is oxidized (ox. # increased).

Past Regents Questions entailing Oxidation or Reduction

June 2007-22 Which transforms occur once Pt2+is reduced?(1) The Pt2+gains electrons and its oxidation number rises.(2) The Pt2+gains electrons and its oxidation number decreases.(3) The Pt2+loses electrons and its oxidation number increases.(4) The Pt2+loses electrons and also its oxidation number decreases.

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Aug 2006-24 Given the well balanced equation representing a redox reaction:2Al + 3Cu2+--> 2Al3++ 3CuWhich statement is true about this reaction?(1) Each Al loses 2e-and also each Cu2+gains 3e-(2) Each Al loses 3e-and also each Cu2+gains 2e-(3) Each Al3+gains 2e-and also each Cu loses 3e-(4) Each Al3+gains 3e-and each Cu loses 2e-

Jan 2006-20 In an oxidation-reduction reaction, reduction is defined as the(1) loss of prolots (3) loss of electrons(2) obtain of protons (4) acquire of electrons

Jan 2005-23 Which adjust in oxidation number suggests oxidation?(1) –1 to +2 (3) +2 to –3(2) –1 to –2 (4) +3 to +2

Aug 2003-27. Given the reaction:


Which statement appropriately describes what occurs when this reaction takes location in a closed system?

A. Atoms of Zn(s) shed electrons and also are oxidized.B. Atoms of Zn(s) acquire electrons and are diminished.C. Tright here is a net loss of mass.D. Tright here is a net gain of mass.

Aug 2003-21. Which type of reaction occurs as soon as nonsteel atoms end up being negative nonsteel ions?

A. oxidationB. reductionC. substitutionD. condensation

Jan 2003-27 When a neutral atom undergoes oxidation, the atom’s oxidation state

(1) decreases as it gains electrons(2) decreases as it loses electrons(3) rises as it gains electrons(4) boosts as it loses electrons


Aug 2002-22 In any redox reactivity, the substance that undergoes reduction will(1) shed electrons and also have actually a decrease in oxidation number(2) shed electrons and also have actually an increase in oxidation number(3) gain electrons and also have actually a decrease in oxidation number(4) obtain electrons and have actually a rise in oxidation number