Question

Ca + Cr2O7{-2} = Ca{2+} + Cr{+3}

Blance the redox please someone help me I got exam tomorrow and I got to go sleep soon

Answer 1

Ca + Cr2O7{-2} = Ca{2+} + Cr{+3}

Ca is zero on left to 2+ on right. delta electron = 2 lost.
Put a 2 in fron of Cr^3+ so we can compare apples with apples.
Ca + Cr2O7{-2} = Ca{2+} + 2Cr{+3}

Now 2 Cr on left are 12+; on right 2Cr^3+ = 6+ so that's a gain of 6 electrons.
Multiply Ca part by 3 and Cr2O7^2- by 1 to get this
3Ca + Cr2O7{-2} = 3Ca{2+} + 2Cr{+3}

Now add 7H2O to balance O, then 14H^+ on left t balance the H.

3Ca + Cr2O7{-2} + 14H^+ = 3Ca{2+} + 2Cr{+3} + 7H2O

3 Ca on left and right.
2 Cr on left and right
7 O on left and right
14 H on left and right.
12+ charge on left; 12+ on right.
:-).
Any questions.

Answer 2

In acidic aqueous solution you use water to balance oxygen and hydrogen cations to balance hydrogen.

Ca = Ca{2+} + 2 ē
Cr2O7{2-} + 14 H{+} + 6 ē = 2 Cr{3+} + 7 H2O
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3 Ca + Cr2O7{2-} + 14 H{+} = 3 Ca{2+} + 2 Cr{3+} + 7 H2O





Ca = Ca²⁺ + 2 e^-
Cr₂O₇^2- + 14 H⁺ + 6 e^- = 2 Cr³⁺ + 7 H₂O
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2 Ca = Ca²⁺ + Cr₂O₇^2- + 14 H⁺ = 2 Ca²⁺ + 2 Cr³⁺ + 7 H₂O

Answer 3

Opps. Cut and paste error.
2 Ca + Cr₂O₇^2- + 14 H⁺ = 2 Ca²⁺ + 2 Cr³⁺ + 7 H₂O