Which of the four reaction steps involve an oxidation-reduction reaction (in whi

Question

Which of the four reaction steps involve an oxidation-reduction reaction (in which the oxidation number of an element changes)? Explain your choice.

1.Reaction of aluminum with KOH (the dissolution step)

................2 Al(s) +2KOH (aq) + 6H2O(l) ->2KAl(OH)4 (aq)+3H2(g)

2.Initial addition of sulfuric acid(precipitation of Al(OH)3)

................2KAl(OH)4 (aq) +H2SO4(aq)->2Al(OH)3(s)+K2SO4(aq)+2H2O(l)

3.Further addition of sulfuric acid(dissolving of Al(OH)3)

................2Al(OH)3(s)+3H2SO4(aq)->Al2(SO4)3(aq)+6H2O(l)

4.Precipitation of alum on cooling

................K2SO4(aq)+Al2(SO4)3(aq)+24H2O ->2 KAl(SO4)2 *12H2O(s)

please answer all parts

Explanation / Answer

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1.Reaction of aluminum with KOH (the dissolution step) (answer)

. Al(s) +2KOH (aq) + 6H2O(l) ->2KAl(OH)4 (aq)+3H2(g)

explanation

Oxidation state of Al = 0

Oxidation state of Al in K Al(OH)4

+1 +x -4 = 0

x=+3

Oxidation state of Al = +3

so Oxidation state of Al increases from zero in Al to +3 in K Al(OH)4 and Al undergoes oxidation

Oxidation state of K in KOH = +1

OH = -1

Oxidation state of H in H2O = +1

O in H2O = -2

Oxidatiion state of H in H2 = zero (on product side)

so oxidation state of H in H2O (+1) decreases to zero (in H2)

H undergoes reduction

so step 1 involves oxidation-reduction reaction

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