Oxidation and reduction: losing and gaining electrons

Answer Key - Grade 10 Science Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   In CO₂, each of the 2 oxygen atoms has oxidation number -2. What is carbon's oxidation number, Ari?

   4
2. 2.

   In SO₃, each of the 3 oxygen atoms has oxidation number -2. What is sulfur's oxidation number, Bo?

   6
3. 3.

   In 4 Fe + 3 O₂ → 2 Fe₂O₃, a simple equation for rusting, which element is oxidized, Jun?

   • Iron
   • Neither
   • Oxygen
4. 4.

   Which two things does iron need around it to rust, Luz?

   • Heat and carbon
   • Oxygen and water
   • Salt and sunlight
5. 5.

   In a zinc–copper cell, zinc atoms become Zn²⁺. Which metal is the anode, where oxidation happens, Milo?

   • Copper
   • Zinc
   • Both metals
6. 6.

   In a zinc–copper cell, which way do electrons flow through the wire, Noah?

   • From the air into the cell
   • From zinc to copper
   • From copper to zinc
7. 7.

   Zinc is oxidized inside an alkaline battery. What happens to the zinc atoms, Pia?

   • They lose electrons
   • They gain protons
   • They gain electrons
8. 8.

   Which reaction is a redox reaction, Ren?

   • AgNO₃ + NaCl → AgCl + NaNO₃
   • Zn + CuSO₄ → ZnSO₄ + Cu
   • HCl + NaOH → NaCl + H₂O
9. 9.

   Is 2 Mg + O₂ → 2 MgO a redox reaction, Tala?

   • No: oxygen is not a metal
   • Yes: Mg goes from 0 to +2
   • No: there are no ions
10. 10.

    Is AgNO₃ + NaCl → AgCl + NaNO₃ a redox reaction, Zee?

    • No: no oxidation number changes
    • Yes: silver swaps its partner
    • Yes: a white solid forms