Step 1. Write down the unbalanced equation (skeleton equation') of the chemical reaction. All reactants and products must be known. For a better result write the reaction in ionic form. Al(s) + NO₂ (aq) AlO₂ (aq) + NH3(aq) Step 2. Separate the process into half reactions. A redox reaction is nothing but both oxidation and reduction reactions taking place simultaneously. a) Assign oxidation numbers for each atom in the equation. Oxidation number (also called oxidation state) is a measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers). O: b) Identify and write out all redox couples in reaction. Identify which reactants are being oxidized (the oxidation number increases when it reacts) and which are being reduced (the oxidation number goes down). Write down the transfer of electrons. Carefully, insert coefficients, if necessary, to make the numbers of oxidized and reduced atoms equal on the two sides of each redox couples. R: O: Practice exercises R: (N) c) Combine these redox couples into two half-reactions: one for the oxidation, and one for the reduction (see: Divide the redox reaction into two half-reactions). O: R: 0 +3-2 Al →AIO₂ + 3e O: +3-2 3+1 NO₂ + 6e → NH3 D. 0 +3-2 Al →AIO₂ + 3e +3-2 3+1 NO₂ + 6e -> NH3 Step 3. Balance the atoms in each half reaction. A chemical equation must have the same number of atoms of each element on both sides of the equation. Add appropriate coefficients (stoichiometric coefficients) in front of the chemical formulas to balance the number of atoms. Never change any formulas. a) Balance all other atoms except hydrogen and oxygen. We can use any of the species that appear in the skeleton equations for this purpose. Keep in mind that reactants should be added only to the left side of the equation and products to the right. +3-2 AIAIO₂ + 3€¯¯ -1 O U b) Balance the charge. For reactions in a basic solution, balance the charge so that both sides have the same total charge by adding an OH ion to the side deficient in negative charge. 0 AI → +3:2 NO₂ + 6e → Ål + +3-2 AIO₂ + 3e 1+ 40H* → +32 Balanced equation 0 +3-2 +3-2 -3+1 Al + NO₂ AIO₂ + NH3 3+1 NH3 +32 3+1 +3e (AI) O BEAV BUTT-H DO THE UP NO STREA EXCLUS TRY IT
Step 1. Write down the unbalanced equation (skeleton equation') of the chemical reaction. All reactants and products must be known. For a better result write the reaction in ionic form. Al(s) + NO₂ (aq) AlO₂ (aq) + NH3(aq) Step 2. Separate the process into half reactions. A redox reaction is nothing but both oxidation and reduction reactions taking place simultaneously. a) Assign oxidation numbers for each atom in the equation. Oxidation number (also called oxidation state) is a measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers). O: b) Identify and write out all redox couples in reaction. Identify which reactants are being oxidized (the oxidation number increases when it reacts) and which are being reduced (the oxidation number goes down). Write down the transfer of electrons. Carefully, insert coefficients, if necessary, to make the numbers of oxidized and reduced atoms equal on the two sides of each redox couples. R: O: Practice exercises R: (N) c) Combine these redox couples into two half-reactions: one for the oxidation, and one for the reduction (see: Divide the redox reaction into two half-reactions). O: R: 0 +3-2 Al →AIO₂ + 3e O: +3-2 3+1 NO₂ + 6e → NH3 D. 0 +3-2 Al →AIO₂ + 3e +3-2 3+1 NO₂ + 6e -> NH3 Step 3. Balance the atoms in each half reaction. A chemical equation must have the same number of atoms of each element on both sides of the equation. Add appropriate coefficients (stoichiometric coefficients) in front of the chemical formulas to balance the number of atoms. Never change any formulas. a) Balance all other atoms except hydrogen and oxygen. We can use any of the species that appear in the skeleton equations for this purpose. Keep in mind that reactants should be added only to the left side of the equation and products to the right. +3-2 AIAIO₂ + 3€¯¯ -1 O U b) Balance the charge. For reactions in a basic solution, balance the charge so that both sides have the same total charge by adding an OH ion to the side deficient in negative charge. 0 AI → +3:2 NO₂ + 6e → Ål + +3-2 AIO₂ + 3e 1+ 40H* → +32 Balanced equation 0 +3-2 +3-2 -3+1 Al + NO₂ AIO₂ + NH3 3+1 NH3 +32 3+1 +3e (AI) O BEAV BUTT-H DO THE UP NO STREA EXCLUS TRY IT
Step 1. Write down the unbalanced equation (skeleton equation') of the chemical reaction. All reactants and products must be known. For a better result write the reaction in ionic form. Al(s) + NO₂ (aq) AlO₂ (aq) + NH3(aq) Step 2. Separate the process into half reactions. A redox reaction is nothing but both oxidation and reduction reactions taking place simultaneously. a) Assign oxidation numbers for each atom in the equation. Oxidation number (also called oxidation state) is a measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers). O: b) Identify and write out all redox couples in reaction. Identify which reactants are being oxidized (the oxidation number increases when it reacts) and which are being reduced (the oxidation number goes down). Write down the transfer of electrons. Carefully, insert coefficients, if necessary, to make the numbers of oxidized and reduced atoms equal on the two sides of each redox couples. R: O: Practice exercises R: (N) c) Combine these redox couples into two half-reactions: one for the oxidation, and one for the reduction (see: Divide the redox reaction into two half-reactions). O: R: 0 +3-2 Al →AIO₂ + 3e O: +3-2 3+1 NO₂ + 6e → NH3 D. 0 +3-2 Al →AIO₂ + 3e +3-2 3+1 NO₂ + 6e -> NH3 Step 3. Balance the atoms in each half reaction. A chemical equation must have the same number of atoms of each element on both sides of the equation. Add appropriate coefficients (stoichiometric coefficients) in front of the chemical formulas to balance the number of atoms. Never change any formulas. a) Balance all other atoms except hydrogen and oxygen. We can use any of the species that appear in the skeleton equations for this purpose. Keep in mind that reactants should be added only to the left side of the equation and products to the right. +3-2 AIAIO₂ + 3€¯¯ -1 O U b) Balance the charge. For reactions in a basic solution, balance the charge so that both sides have the same total charge by adding an OH ion to the side deficient in negative charge. 0 AI → +3:2 NO₂ + 6e → Ål + +3-2 AIO₂ + 3e 1+ 40H* → +32 Balanced equation 0 +3-2 +3-2 -3+1 Al + NO₂ AIO₂ + NH3 3+1 NH3 +32 3+1 +3e (AI) O BEAV BUTT-H DO THE UP NO STREA EXCLUS TRY IT
I'm balancing redox reactions from examples. Can someone explain why 3e- was added on the Right side in step3? Do we ignore that the overall charge of AlO3 was -1? Just having trouble unders
Transcribed Image Text:Step 1. Write down the unbalanced equation (skeleton equation') of the chemical reaction. All reactants and products
must be known. For a better result write the reaction in ionic form.
Al(s) + NO₂ (aq)
AlO₂ (aq) + NH3(aq)
Step 2. Separate the process into half reactions. A redox reaction is nothing but both oxidation and reduction reactions
taking place simultaneously.
a) Assign oxidation numbers for each atom in the equation. Oxidation number (also called oxidation state) is a
measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers).
O:
b) Identify and write out all redox couples in reaction. Identify which reactants are being oxidized (the oxidation
number increases when it reacts) and which are being reduced (the oxidation number goes down). Write down the
transfer of electrons. Carefully, insert coefficients, if necessary, to make the numbers of oxidized and reduced atoms
equal on the two sides of each redox couples.
R:
Practice exercises
0:
R:
0
+3-2
Al → AIO₂ + 3e
(N)
c) Combine these redox couples into two half-reactions: one for the oxidation, and one for the reduction (see: Divide
the redox reaction into two half-reactions).
R:
+3-2
NO₂ + 6e
O:
-3+1
NH3
D.
0
+3-2
Al →AIO₂ + 3e
+3-2
3+1
NO₂ + 6e NH3
Step 3. Balance the atoms in each half reaction. A chemical equation must have the same number of atoms of each
element on both sides of the equation. Add appropriate coefficients (stoichiometric coefficients) in front of the chemical
formulas to balance the number of atoms. Never change any formulas.
a) Balance all other atoms except hydrogen and oxygen. We can use any of the species that appear in the skeleton
equations for this purpose. Keep in mind that reactants should be added only to the left side of the equation and
products to the right.
+3-2
0
+3-2
O:
Ål → AlO₂ + 36° Al → A1O₂ + 3€
Al
3e
-1
+3-2
NO₂ + 6e
Balanced equation
0
+3-2
+3-2
Al + NO₂ AIO₂ + NH3
= +NH,
-
-3+1
NH3
+3-2
Ål + 40H* → ÄIÓ₂ + 3e
b) Balance the charge. For reactions in a basic solution, balance the charge so that both sides have the same total
charge by adding an OH ion to the side deficient in negative charge.
3+1
(AI)
JALL
כ
BEAV
BUTT-H
DO THE UP
NO
STREA
EXCLUS
TRY IT
Method Method Redox reactions are generally balanced using two processes. The first method is based on the redox reaction’s division into two reactions where one is involved in oxidation and the other in reduction (half reaction method) and the second one is based on the reducing and oxidizing molecule’s oxidation number variation (oxidation number method).
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