Writing equations of redox reactions
In the electron balance method the numbers of electrons given and accepted are made equal. Steps: 1) write the scheme; 2) find the elements whose state changes; 3) write a half-reaction for each: Al⁰ – 3e⁻ → Al³⁺, 2H⁺ + 2e⁻ → H₂⁰; 4) find the least common multiple of the electron numbers and put extra multipliers (2 for Al, 3 for H); 5) write these as coefficients for the oxidizing and reducing agents; 6) balance the remaining atoms (metal, acid residue, hydrogen, oxygen). Result: 2Al + 6HCl → 2AlCl₃ + 3H₂. At the end each element must have equal atom numbers on both sides. These equations are written on paper only; the experiment of a metal with acid is never done at home.
“Scales”: use two sheets of paper as pans: write “electrons given” on the left and “electrons accepted” on the right. Balance Cu + AgNO₃ → Cu(NO₃)₂ + Ag with cards (each card = 1 electron). Paper only.