Presentation on theme: "Step 1: Write the unbalanced formula equations"— Presentation transcript:
1 Step 1: Write the unbalanced formula equations PROBLEM: Aqueous Sodium Hydroxide plus aqueous Calcium Hydroxide plus solid Carbon plus Chlorine dioxide gas yields aqueous Sodium Chlorite plus solid calcium carbonate plus liquid water. (Note: The reaction takes place in basic solution)Step 1: Write the unbalanced formula equationsNaOH(aq) + Ca(OH)2(aq) + C(s) + ClO2(g) > NaClO2(aq) + CaCO3(s) + H2O(l)Step 2: Identify the species that are oxidized and reduced. Start by labeling the oxidation #s.NaOH(aq) + Ca(OH)2(aq) + C(s) + ClO2(g) > NaClO2(aq) + CaCO3(s) + H2O(l)+1+2–2+3+4Since C goes from 0 to +4 it lost e– and is oxidized.Since Cl goes from +4 to +3 it gained e– and is reduced.Now we will balance the equation as if it was in acid and then switch it to base after we have the net ionic equationStep 3: Write and balance the oxidation half reaction. Note – since CaCO3 is a solid it does NOT dissociateC > CaCO3Since the C is already balanced, balance the Ca by adding Ca2+Ca C > CaCO3Next add 3 H2O to balance the O mass3H2O + Ca C > CaCO3Next balance the H mass by adding 6H+3H2O + Ca C > CaCO H+Next add e– to balance the charge – since the left is +2, and the right is +6, add 4e– to the right3H2O + Ca C > CaCO H e–
2 Step 4: Write and balance the reduction half reaction ClO2(g) > ClO2–Mass is already balanced so add e– to balance the charge – just add 1 e–e– + ClO2(g) > ClO2–Step 5: Next make the oxidation and reduction half-reactions have the same # of e–3H2O + Ca C > CaCO H e–e– + ClO > ClO2– (X4)4 e– + 4 ClO > 4 ClO2–Step 6: Combine the two half-reactions together, to make the net ionic equation. Remember to cancel out the items on opposite sides of arrow (water, H+ ions, and e–). In this case in only the e– cancel out.3 H2O + Ca C ClO > 4 ClO2– + CaCO H+Step 7: Convert to base by adding an OH– ion for every H+ ion. But remember – to keep the equation balanced you must add to both sides.6 OH– H2O + Ca C ClO > 4 ClO2– + CaCO H OH–Step 8: OH– plus H+ makes water – combine and cancel out waters from both sides6 OH– H2O + Ca C ClO > 4 ClO2– + CaCO H2O6 OH– + Ca C ClO > 4 ClO2– + CaCO H2O
3 4 NaOH– + Ca(OH)2 + C + 4 ClO2 --------> 4 NaClO2 + CaCO3 + 3 H2O Step 7: Add back spectator ions and combine with other ions to write complete compounds and the balanced overall equation. Combine Ca2+ and OH–. Then add Na+ where needed to anions.4 NaOH– + Ca(OH)2 + C ClO > 4 NaClO2 + CaCO H2O
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