Use oxidation numbers to decide whether the following is a redox reaction. If so, then identify the oxidizing agent and the reducing agent. Explain your answer. 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g)
Answers
Answer:
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Explanation:
Step 1. Write the oxidation numbers for each atom:
A
l
+
H
2
S
O
4
-->
A
l
2
(
S
O
4
)
3
+
H
2
0 +1 +6 -2-2 +3 +6 -2-2 0
+1 -2-2 +3 -2-2
Step 2. Identify what has been oxidised and what as been reduced, and balance the equation ONLY for these species
Al has been oxidised 0 to +3. We need 2Al on the LHS as we have 2 on the right.
Hydrogen has been reduced from +1 to 0. We are balanced for H, so the equation at this stage looks like:
2
A
l
+
H
2
S
O
4
-->
A
l
2
(
S
O
4
)
3
+
H
2
Step 3. Calculate the total increase in oxidation numbers due to the oxidation taking place. We are oxidising 2 x Al (oxidation state 0) to 2 x Al3+ (oxidation state +3) so the total increase is +6.
Do the same for the reduction. We reduce 2 x H+ (+1) to 2 x H (0) so the total decrease is -2
Step 4. Multiply the the species being oxidised and/or reduced so that the total increase in oxidation number = total decrease in oxidation number. In this example we need to multiply the species involved in the reduction of hydrogen x3 to get a total decrease of -6. This means we need 3H2SO4 and we get 3H2.