CHEM: REDOX REACTIONS DYNAMIC MODULE

In the reaction shown below, which substance is reduced? 3 Na(s) + AlCl3(aq) → 3 NaCl(aq) + Al(s)

aluminum in AlCl3(aq)

In the reaction shown below, which substance is reduced? 3 CuCl2(aq) + 2 Al(s) → 2 AlCl3(aq) + 3 Cu(s)

copper in CuCl2(aq) The oxidation state on the copper in CuCl2, is +2, as there are two chlorine atoms, each with a −1 oxidation state. For the compound to be neutral, the copper atom must have a +2 oxidation state. The sum of the oxidation states must equal zero for a neutral compound. (1 Cu)(+2) + (2 Cl)(−1) = 0 2 + (-2) = 0

What is the oxidation state of nitrogen in NH4+?

−3 (1 N)(x) + (4 H)(+1) = +1 x + 4 = +1 x = −3

What is the oxidation state of sulfur in Na2S2O3?

+2

In the reaction shown below, which substance is oxidized? 2 Fe3+(aq) + Sn2+(aq) → 2 Fe2+(aq) + Sn4+(aq)

Sn2+(aq)

Which substance is the oxidizing agent in the following reaction? 2 NH3(aq) + OCl−(aq) → N2H4(aq) + H2O(l) + Cl−(aq)

OCl−(aq) 2 NH3(aq) + OCl−(aq) → N2H4(aq) + H2O(l) + Cl−(aq) The oxidation state of nitrogen goes from −3 to −2. The oxidation state of chlorine goes from −3 to −1. The oxidation state of oxygen is −2 and of hydrogen is +1 and neither changes in this reaction. In the process, NH3(aq) is oxidized to N2H4(aq), and OCl−(aq) is reduced to Cl−(aq). The species that is oxidized, NH3(aq), is the reducing agent, and the species that is reduced, OCl−(aq), is the oxidizing agent.

What is the oxidation state of carbon in glucose, C6H12O6?

0 (6 C)(x) + (12 H)(+1) + (6 O)(−2) = 0 6x + 12 + (−12) = 0 6x = 0 x = 0

In the reaction shown below, which substance is reduced? Mg0(s) + Ag2+(aq) → Mg2+(aq) + Ag0(s)

Ag2+(aq) Ag2+(aq) is reduced to Ag0(s), as the oxidation state decreases from +2 to 0. Mg0(s) + Ag2+(aq) → Mg2+(aq) + Ag0(s) A decrease in the oxidation state occurs due to reduction, as electrons are gained, while an increase in oxidation state is due to oxidation, as electrons are lost. Mg0(s) is oxidized to Mg2+(aq) in this reaction.

In the reaction shown below, which substance is oxidized? Al0(s) + Cr3+(aq) → Al3+(aq) + Cr0(s)

Al0(s) Why? Al0(s) is oxidized to Al3+(aq), as the oxidation state increases from 0 to +3. Al0(s) + Cr3+(aq) → Al3+(aq) + Cr0(s) A decrease in the oxidation state occurs due to reduction, as electrons are gained, while an increase in oxidation state is due to oxidation, as electrons are lost.

Which substance is the oxidizing agent in the following reaction? 2 Au3+(aq) +6 I−(aq) → 2 Au0(s) + 3 I20(s)

Au3+(aq) Au3+(aq) is the oxidizing agent as it causes I-(aq) to be oxidized to I20(s). I−(aq) is oxidized as the oxidation state increases from −1 to 0. 2 Au3+(aq) +6 I−(aq) → 2 Au0(s) + 3 I20(s) In the process, Au3+(aq) is reduced to Au0(s). The species that is oxidized is the reducing agent, and the species that is reduced is the oxidizing agent.

Which substance is the reducing agent in the following reaction? Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g)

CO(g)

In the reaction shown below, which substance is oxidized? Ca0(s) + Pb2+(aq) → Ca2+(aq) + Pb0(s)

Ca0(s) Ca0(s) is oxidized to Ca2+(aq), as the oxidation state increases from 0 to +2. Ca0(s) + Pb2+(aq) → Ca2+(aq) + Pb0(s) A decrease in the oxidation state occurs due to reduction, as electrons are gained, while an increase in oxidation state is due to oxidation, as electrons are lost. Pb2+(aq) is reduced to Pb0(s) in this reaction.

Which substance is the reducing agent in the following reaction? Co0(s) + Pt2+(aq) → Pt0(s) + Co2+(aq)

Co0(s) Co0(s) is the reducing agent as it causes Pt2+(aq) to be reduced to Pt0(s). Pt2+(aq) is reduced as the oxidation state decreases from +2 to 0. Co0(s) + Pt2+(aq) → Pt0(s) + Co2+(aq) In the process, Co0(s) is oxidized to Co2+(aq). The species that is oxidized is the reducing agent, and the species that is reduced is the oxidizing agent.

Which substance is the reducing agent in the following reaction? CO2(g) + H2(g) → 2 CO(g) + H2O(g)

H2(g) The oxidation state of carbon goes from +4 to +2. The oxidation state of hydrogen goes from 0 to +1. The oxidation state of oxygen is −2 and does not change in this reaction. In the process, CO2(g) is reduced to CO(g), and H2(g) is oxidized to H2O(g). The species that is oxidized, H2(g), is the reducing agent, and the species that is reduced, CO2(g), is the oxidizing agent.

In the reaction shown below, which substance is reduced? Fe0(s) + Ni3+(aq) → Fe3+(aq) + Ni0(s)

Ni3+(aq)

What is the oxidation state of nitrogen in Mg(NO2)2?

+3

What is the oxidation state of chlorine in HClO2?

+3 (1 H)(+1) + (1 Cl)(x) + (2 O)(−2) = 0 1 + x + (−4) = 0 x + (−3) = 0 x = 3

What is the oxidation state of boron in Na2B4O7?

+3 (2 Na)(+1) + (4 B)(x) + (7 O)(−2) = 0 2 + 4x + (−14) = 0 4x + (−12) = 0 4x = 12 x = 3

What is the oxidation state of sulfur in HSO3−?

+4 (1 H)(+1) + (1 S)(x) + (3 O)(−2) = −1 1 + x + (−6) = −1 x + (−5) = −1 x = 4

What is the oxidation state of silicon in SiO32−?

+4 (1 Si)(x) + (3 O)(−2) = −2 x + (−6) = −2 x = 4

What is the oxidation state of carbon in Al2(CO3)3?

+4 (2 Al)(+3) + (3 C)(x) + (9 O)(−2) = 0 6 + 3x + (−18) = 0 3x + (−12) = 0 3x = 12 x = 4

What is the oxidation state of iodine in IO3−?

+5 (1 I)(x) + (3 O)(−2) = −1 x + (−6) = −1 x = 5

What is the oxidation state of nitrogen in N2O5?

+5 (2 N)(x) + (5 O)(−2) = 0 2x + (−10) = 0 2x = 10 x = 5

What is the oxidation state of phosphorus in H3PO4?

+5 (3 H)(+1) + (1 P)(x) + (4 O)(−2) = 0 3 + x + (−8) = 0 x + (−5) = 0 x = 5

What is the oxidation state of chromium in K2Cr2O7?

+6

What is the oxidation state of sulfur in H2SO4?

+6 (2 H)(+1) + (1 S)(x) + (4 O)(−2) = 0 2 + x + (−8) = 0 x + (−6) = 0 x = 6

What is the oxidation state of manganese in KMnO4?

+7 (1 K)(+1) + (1 Mn)(x) + (4 O)(−2) = 0 1 + x + (−8) = 0 x + (−7) = 0 x = 7

Which substance is the reducing agent in the following reaction? Fe(s) + CuSO4(aq) → Cu(s) + FeSO4(aq)

Fe(s) The oxidation state on the copper atom in CuSO4(aq), is +2, as the charge on the sulfate ion, SO4−2, is −2. The oxidation state on solid copper, Cu(s), is 0. Notice that the copper in CuSO4(aq) is reduced as its oxidation state decreases from +2 to 0. In the process, the Fe(s) atom is oxidized to FeSO4(aq). The oxidation state on solid iron, Fe(s), is 0. The oxidation state on the iron atom in FeSO4 (aq), is +2, as the charge on the sulfate ion, SO4−2, is −2. Therefore, iron is oxidized as the oxidation state increases from 0 to +2. The species that is oxidized is the reducing agent, and the species that is reduced is the oxidizing agent.

In the reaction shown below, which substance is oxidized? 2 Cr(s) + Fe2O3(aq) → Cr2O3(aq) + 2 Fe(s)

Cr(s) The oxidation state on the chromium in Cr2O3, is +3, as there are three oxygen atoms, each with a −2 oxidation state. For the compound to be neutral, the two chromium atoms must each have a +3 oxidation state. The sum of the oxidation states must equal zero for a neutral compound. (2 Cr)(+3) + (3 O)(−2) = 0 6 + (-6) = 0

Which substance is the oxidizing agent in the following reaction? Mg(s) +2 HCl(aq) → H2(g) + MgCl2(aq)

hydrogen in HCl(aq) The oxidation state on solid magnesium, Mg(s), is 0, while the oxidation state on magnesium in MgCl2(aq) is +2. Notice that Mg(s) is oxidized as the oxidation state increases from 0 to +2. In the process, the hydrogen in HCl(aq) is reduced to H2(g). The oxidation state on hydrogen gas, H2(g), is 0, while the oxidation state on the hydrogen atom in HCl(aq) is +1. Therefore, hydrogen is reduced as the oxidation state decreases from +1 to 0. The species that is oxidized is the reducing agent, and the species that is reduced is the oxidizing agent.