Answer: The balanced equation is
Cr
2
O
2-
7
+
3SO
2-
3
+
8H
+
→
2Cr
3+
+
3SO
2-
4
+
4H
2
O
Step-by-step explanation:
Step 1: Separate the skeleton equation into two half-reactions.
Cr
2
O
2-
7
→
Cr
3+
SO
2-
3
→
SO
2-
4
Step 2: Balance all atoms other than
H
and
O
.
Cr
2
O
2-
7
→
2Cr
3+
SO
2-
3
→
SO
2-
4
Step 3: Balance
O
.
Add enough
H
2
O
molecules to balance
O
.
Cr
2
O
2-
7
→
2Cr
3+
+
7
H
2
O
SO
2-
3
+
H
2
O
→
SO
2-
4
Step 4: Balance
H
.
Add enough
H
+
ions to balance
H
.
Cr
2
O
2-
7
+
14H
+
→
2Cr
3+
+
7
H
2
O
SO
2-
3
+
H
2
O
→
SO
2-
4
+
2H
+
Step 5: Balance charge.
Add electrons to the side that needs more negative charge.
Cr
2
O
2-
7
+
14H
+
+
6
e
-
→
2Cr
3+
+
7
H
2
O
SO
2-
3
+
H
2
O
→
SO
2-
4
+
2H
+
+
2
e
-
Step 6: Equalize electrons transferred.
Multiply each half-reaction by numbers to get the lowest common multiple of electrons transferred.
1
×
[
Cr
2
O
2-
7
+
14H
+
+
6
e
-
→
2Cr
3+
+
7
H
2
O
]
3
×
[
SO
2-
3
+
H
2
O
→
SO
2-
4
+
2H
+
+
2
e
-
]
Step 7: Add the two half-reactions.
Cr
2
O
2-
7
+
8
14
H
+
+
6
e
-
→
2Cr
3+
+
4
7
H
2
O
3
SO
2-
3
+
3
H
2
O
→
3SO
2-
4
+
6H
+
+
6
e
-
m
m
m
m
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
Cr
2
O
2-
7
+
3SO
2-
3
+
8H
+
→
2Cr
3+
+
3SO
2-
4
+
4H
2
O
Step-by-step explanation: