Understanding Redox Reactions Quiz

• +4

• +6

• -2

• 0

Answer explanation

In H2SO4, the total oxidation state of oxygen is -8 (4 O atoms at -2 each). Hydrogen contributes +2 (2 H atoms at +1 each). To balance, sulfur must have an oxidation number of +6, making the correct answer +6.

Which of the following reactions is a redox reaction?

Answer explanation

The reaction H2 + Cl2 → 2HCl is a redox reaction because hydrogen is oxidized (loses electrons) and chlorine is reduced (gains electrons), resulting in a change in oxidation states.

Tags

NGSS.HS-PS1-2

Answer explanation

In the reaction, Zn is oxidized as it loses two electrons to form Zn^{2+}. Cu^{2+} is reduced to Cu, while Zn^{2+} and Cu are the products. Therefore, the species that is oxidized is Zn.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Answer explanation

In acidic solution, MnO4^- is reduced to Mn^2+ and Fe^2+ is oxidized to Fe^3+. Balancing gives 5Fe^{2+} and 8H^+ to balance charges and atoms, resulting in MnO_4^- + 5Fe^{2+} + 8H^+ → Mn^{2+} + 5Fe^{3+} + 4H_2O.

Which of the following statements is true about an electrochemical cell?

• Electrons flow from the cathode to the anode.

• Oxidation occurs at the cathode.

• Reduction occurs at the anode.

• Electrons flow from the anode to the cathode.

Answer explanation

In an electrochemical cell, electrons flow from the anode (where oxidation occurs) to the cathode (where reduction occurs). Therefore, the correct statement is that electrons flow from the anode to the cathode.

Tags

NGSS.HS-PS3-5

• +1.10 V

• -1.10 V

• +0.42 V

• -0.42 V

Answer explanation

To find the standard cell potential, use the formula: E°cell = E°(cathode) - E°(anode). Here, Cu is reduced (cathode) and Zn is oxidized (anode). Thus, E°cell = 0.34 V - (-0.76 V) = +1.10 V.

Answer explanation

In the reaction, aluminum (Al) donates electrons to copper ions (Cu^{2+}), reducing them to copper (Cu). Therefore, Al is the reducing agent as it undergoes oxidation to Al^{3+}.

Tags

NGSS.HS-PS1-2

• +3

• +6

• +7

• +2

Answer explanation

In K2Cr2O7, the total oxidation state of oxygen is -14 (7 x -2). Potassium (K) has an oxidation state of +1 (2 x +1 = +2). To balance, chromium must have a total oxidation state of +12 (2Cr = +12), giving each Cr an oxidation number of +6.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which of the following half-reactions represents the reduction process?

Tags

NGSS.HS-PS1-2

NGSS.HS-PS1-7

What is the oxidation number of N in NO₂^1- ?

• -3

• +4

• -2

• +3

Answer explanation

In NO2^1-, the overall charge is -1. Oxygen has an oxidation number of -2 (2 O = -4). Let x be the oxidation number of N. The equation is x + (-4) = -1, solving gives x = +3. Thus, the oxidation number of N is +3.

Tags

NGSS.HS-PS1-1