bowlinL7252 2 years ago Hi guys, one question with a couple of parts! What is the oxidation state for the atoms in the reaction: 2Al + 8H2O → 2H+1 + 3H2 + 2Al(OH)4-1 a) Elemental aluminum (Al) b) One hydrogen atom in H2O c) One oxygen atom in H20 d) Elemental hydrogen (H) e) One aluminum atom in Al(OH)4-1 f) One oxygen atom in Al(OH)4-1 g) One hydrogen atom in Al(OH)4-1

1. aaronq

oxidation state on homonuclear molecules or elemental species = 0

2. aaronq

Oxygen = -2 always

3. aaronq

you can figure out the rest by balancing the charges

4. bowlinL7252

Alright, so for a i got 0, b -3, c -2, d 1, e 2, f -2 and g 0. Are these right?

5. Frostbite

Let me see if I get this right: You suggest that hydrogen in water have the oxidation number -3?

6. bowlinL7252

I believe so

7. Frostbite

Okay. We need an additional rule: "The sum of oxidations numbers most equal to total charge of the molecule." So when we look at water it have no charge... sense oxygen always get -2 each hydrogen most be what?

8. bowlinL7252

-5? And in that equation, which element was reduced and which was oxidized?

9. bowlinL7252

10. Frostbite

Best you get some training, so I'm gonna start with water and we take them each by each. H2O we take notice: Total charge = 0 oxygen always -2 Hydrogen always +1 This also make sense we should say: 0=-2+2*x <-> x=+1

11. Frostbite

aluminum is right. again it does not have charge and is an elemental species.

12. bowlinL7252

Both hydrogens are positive one as well?

13. Frostbite

Yes. it is 2 times +1

14. bowlinL7252

Alright, so what about for e through g?

15. bowlinL7252

hello?

16. Frostbite

Sorry I was thinking. both e and g are wrong.

17. Frostbite

The oxidation state of oxygen is -2 the oxidation state of hydrogen is +1: so we get: Al(OH)4 -1 -1 = -8+4+x Here is x the oxidation state of Al.. What is x?

18. Frostbite

Not quite.

19. Frostbite

\[-1=-8+4+x\] \[x=-1+8-4=3\]

20. bowlinL7252

So aluminum was reduced, so which was oxidized?

21. aaronq

which one are you working on?

22. bowlinL7252

g

23. bowlinL7252

I need the answer for g and then: In the equation above, which element was reduced and which element was oxidized?

24. aaronq

The H on the compound is part of the hydroxide ion, which is OH^- since O is -2 and theres a -1 charge on ion, H is +1

25. bowlinL7252

Awesome. so then which was oxidized and which was reduced?

26. aaronq

they're both 0 when not part of a molecule, if one gains e then we say its reduced because it became more negative, the opposite is for oxidized.

27. bowlinL7252

I mean for all of the elements in the equations, it seems like aluminum gained electrons

28. bowlinL7252

!

29. aaronq

we already did everything in the equation

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