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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: /0 on October 26, 2008, 03:19:18 am

Title: some redox questions
Post by: /0 on October 26, 2008, 03:19:18 am: Hi I need help with these wtf questions (why do wtf questions come up so regularly in chemistry :( ), thaaaaaaanks

Predict if a spontaneous reaction will occur if Iodine is mixed with aluminium. If so, write the overall ionic equation.

Answer: $Al(s)+I_2(s) \rightarrow AlI_3(s)$

This question is quite wtf because
1. Iodine is not given on the electrochemical series in the book
2. No states are given
3. The equation in the answer is not even balanced
4. Doesn't look like a redox to me

How do you do that question?

Also:

Predict if a spontaneous reaction will occur if Chlorine gas is mixed with magnesium. If so, write the equation etcetc

Answer: $Mg(s) + Cl_2(g) \rightarrow MgCl_2(s)$

Is this meant to be a trick question? Is it just an ionic bonding equation in a redox chapter?
Title: Re: some redox questions
Post by: bec on October 26, 2008, 07:50:34 am: Quote from: DivideBy0 on October 26, 2008, 03:19:18 am
Predict if a spontaneous reaction will occur if Iodine is mixed with aluminium. If so, write the overall ionic equation.

Answer: $Al(s)+I_2(s) \rightarrow AlI_3(s)$

This question is quite wtf because
1. Iodine is not given on the electrochemical series in the book
2. No states are given
3. The equation in the answer is not even balanced
4. Doesn't look like a redox to me

1. Iodine is in the electrochemical series. Print the VCAA one off, it's probably different to what's in your book and you need to get used to it anyway...
2. States are given in the electrochem series (the VCAA one anyway)
3. You're right, it's not balanced. I got $3I_2 + 2Al \rightarrow 2ALI_3$
4. It is - iodine gains electrons, aluminium loses them - if you had iodine on your electrochem series you wouldn't have a problem identifying this though

Quote from: DivideBy0 on October 26, 2008, 03:19:18 am
Predict if a spontaneous reaction will occur if Chlorine gas is mixed with magnesium. If so, write the equation etcetc

Answer: $Mg(s) + Cl_2(g) \rightarrow MgCl_2(s)$

Is this meant to be a trick question? Is it just an ionic bonding equation in a redox chapter?

Same deal - you're probably just looking at the wrong electrochemical series
Pretty sure the book is right.

But....just a note...take everything I say with a grain of salt because I'm usually wrong in chem and maths...
Title: Re: some redox questions
Post by: /0 on October 26, 2008, 02:16:06 pm: thanks bec, so I guess ionic bonding is a form of redox?
Title: Re: some redox questions
Post by: bec on October 26, 2008, 02:30:46 pm: Redox is any reaction involving reduction of one substance, and oxidation of another.

Look at the oxidation numbers here:
$2Ag(s) + Cl_2(g) \rightarrow 2AgCl(s)$

Ag's ox number goes from 0 to +1 (ie, it is OXIDISED)
Cl's ox number goes from 0 to -1 (ie, it is REDUCED)

I guess you could say that ionic bonding "is" redox but you're better off just looking at the specific reaction and working it out yourself using oxidation numbers - it should only take a second.
You have to be careful making generalisations like 'all ionic bonding is redox' because you might end up saying that something like $Ag^{+}(aq) + Cl^{-}(aq) \rightarrow AgCl(s)$ is redox, when it clearly isn't.
Title: Re: some redox questions
Post by: /0 on October 26, 2008, 02:38:22 pm: Ah that makes things clearer thx bec