QuestionJuly 1, 2025

Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front of H2O and Cr2(SO4)3 in the balanced reaction? C3H8O2(aq)+K2Cr2O7(aq)arrow C3H4O4(aq)+Cr2(SO4)3(aq) A H2O=22,Cr2(SO4)3=4 B H2O=11,Cr2(SO4)3=4 C H2O=5,Cr2(SO4)3=2 D H2O=8,Cr2(SO4)3=2 E H2O=1,Cr2(SO4)3=5

Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front of H2O and Cr2(SO4)3 in the balanced reaction? C3H8O2(aq)+K2Cr2O7(aq)arrow C3H4O4(aq)+Cr2(SO4)3(aq) A H2O=22,Cr2(SO4)3=4 B H2O=11,Cr2(SO4)3=4 C H2O=5,Cr2(SO4)3=2 D H2O=8,Cr2(SO4)3=2 E H2O=1,Cr2(SO4)3=5
Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front of H2O and Cr2(SO4)3 in the
balanced reaction?
C3H8O2(aq)+K2Cr2O7(aq)arrow C3H4O4(aq)+Cr2(SO4)3(aq)
A H2O=22,Cr2(SO4)3=4
B H2O=11,Cr2(SO4)3=4
C H2O=5,Cr2(SO4)3=2
D H2O=8,Cr2(SO4)3=2
E H2O=1,Cr2(SO4)3=5

Solution
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Answer

D H_2O=8,Cr2(SO_4)_3=2 Explanation 1. Assign Oxidation States Determine oxidation states for each element in the reactants and products. Propane-1,2-diol (C_3H_8O_2) is oxidized to malonic acid (C_3H_4O_4), and dichromate ion (Cr_2O_7^{2-}) is reduced to chromium sulfate (Cr_2(SO_4)_3). 2. Write Half-Reactions Oxidation: C_3H_8O_2 \rightarrow C_3H_4O_4 + 4H^+ + 4e^- Reduction: Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O 3. Balance Electrons Multiply oxidation half-reaction by 3 and reduction half-reaction by 2 to balance electrons: 3(C_3H_8O_2 \rightarrow C_3H_4O_4 + 4H^+ + 4e^-) 2(Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O) 4. Combine Half-Reactions Combine balanced half-reactions: 3C_3H_8O_2 + 2Cr_2O_7^{2-} + 28H^+ \rightarrow 3C_3H_4O_4 + 4Cr^{3+} + 14H_2O 5. Convert Ions to Compounds Convert ions to compounds using stoichiometry: 3C_3H_8O_2 + K_2Cr_2O_7 + 28H^+ \rightarrow 3C_3H_4O_4 + 2Cr_2(SO_4)_3 + 14H_2O 6. Verify Coefficients Check coefficients for H_2O and Cr_2(SO_4)_3: H_2O = 14, Cr_2(SO_4)_3 = 2

Explanation

1. Assign Oxidation States<br /> Determine oxidation states for each element in the reactants and products. Propane-1,2-diol ($C_3H_8O_2$) is oxidized to malonic acid ($C_3H_4O_4$), and dichromate ion ($Cr_2O_7^{2-}$) is reduced to chromium sulfate ($Cr_2(SO_4)_3$).<br /><br />2. Write Half-Reactions<br /> Oxidation: $C_3H_8O_2 \rightarrow C_3H_4O_4 + 4H^+ + 4e^-$ <br /> Reduction: $Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$<br /><br />3. Balance Electrons<br /> Multiply oxidation half-reaction by 3 and reduction half-reaction by 2 to balance electrons: <br /> $3(C_3H_8O_2 \rightarrow C_3H_4O_4 + 4H^+ + 4e^-)$ <br /> $2(Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O)$<br /><br />4. Combine Half-Reactions<br /> Combine balanced half-reactions: <br /> $3C_3H_8O_2 + 2Cr_2O_7^{2-} + 28H^+ \rightarrow 3C_3H_4O_4 + 4Cr^{3+} + 14H_2O$<br /><br />5. Convert Ions to Compounds<br /> Convert ions to compounds using stoichiometry: <br /> $3C_3H_8O_2 + K_2Cr_2O_7 + 28H^+ \rightarrow 3C_3H_4O_4 + 2Cr_2(SO_4)_3 + 14H_2O$<br /><br />6. Verify Coefficients<br /> Check coefficients for $H_2O$ and $Cr_2(SO_4)_3$: $H_2O = 14$, $Cr_2(SO_4)_3 = 2$
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