Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: junbumkim on May 27, 2007, 05:02:45 AM
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I am studying for PCAT, and couldn't understand some basic reactions..
I'd appreciate if you one of you experts could give me a detailed explanations on these following reactions..I am studying by myself, so it's hard to look for a person to get help from..
1. An excess amount of cholorine gas is passed over hot iron fillings.
Cl2 + F --> FeCl3 , in this reaction, why does Fe have +3
charge in the product? Couldn't it have +2 ?
2. Solid litium hydride is added to water
LiH + H2O -> Li+ + OH- + H2(g)
Would I be wrong to say if it just formed LiOH and more water instead of H2
gas? How can one know it forms H2?
3. A concentrated solution of ammonia is added to a solution of Zinc Iodide
NH3 + ZnI2 ---> Zn(OH)2 + NH4+
Where does OH come from?
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1. An excess amount of cholorine gas is passed over hot iron fillings.
Cl2 + F --> FeCl3 , in this reaction, why does Fe have +3
charge in the product? Couldn't it have +2 ?
Yes, the two most common oxidation states of iron are +3 and +2. I don't know how you would tell which form gets created in your reaction (note, your reaction is not balanced).
2. Solid litium hydride is added to water
LiH + H2O -> Li+ + OH- + H2(g)
Would I be wrong to say if it just formed LiOH and more water instead of H2
gas? How can one know it forms H2?
This is an acid/base reaction. However, it is a strange acid/base reaction because the hydride ion (H-) is acting as your base. As in a normal acid/base reaction, the base picks up the proton from your acid (H2O), creating H2. This leaves behind an Li+ ion and a OH- ion. The reaction you have written will not work (for example, try to balance the reaction that you have written).
3. A concentrated solution of ammonia is added to a solution of Zinc Iodide
NH3 + ZnI2 ---> Zn(OH)2 + NH4+
Where does OH come from?
In the presence of water, ammonia reacts to form NH4OH.
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1. An excess amount of cholorine gas is passed over hot iron fillings.
Cl2 + F --> FeCl3 , in this reaction, why does Fe have +3
charge in the product? Couldn't it have +2 ?
Yes, the two most common oxidation states of iron are +3 and +2. I don't know how you would tell which form gets created in your reaction (note, your reaction is not balanced).
Cl2 is a strong oxidizer and always Fe(III) compound will be obtained in this reaction
But in this reaction
Fe + 2HCl = FeCl2 + H2
in the persence of a strong reductor (H2 in this case ) only Fe(II) compounds can be obtained
]2. Solid litium hydride is added to water
LiH + H2O -> Li+ + OH- + H2(g)
Would I be wrong to say if it just formed LiOH and more water instead of H2
gas? How can one know it forms H2?
This is an acid/base reaction. However, it is a strange acid/base reaction because the hydride ion (H-) is acting as your base. As in a normal acid/base reaction, the base picks up the proton from your acid (H2O), creating H2. This leaves behind an Li+ ion and a OH- ion. The reaction you have written will not work (for example, try to balance the reaction that you have written).
This reaction will proceed vigorously
3. A concentrated solution of ammonia is added to a solution of Zinc Iodide
NH3 + ZnI2 ---> Zn(OH)2 + NH4+
Where does OH come from?
In the presence of water, ammonia reacts to form NH4OH.
Concentrated water solution of ammonia will form [Zn(NH3)4]2+ cation
Stoichometric amount of diluted ammonia will form:
ZnI2 + 2NH3 +2H2O = Zn(OH)2(s) + 2NH4+ + 2I-
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Thanks a lot for your help.
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Cl2 is a strong oxidizer and always Fe(III) compound will be obtained in this reaction
But in this reaction
Fe + 2HCl = FeCl2 + H2
in the persence of a strong reductor (H2 in this case ) only Fe(II) compounds can be obtained
I would rather say that H+ is too weak oxidizer (E=0) to oxidize Fe2+ further (required potential being 0.77).
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its because chlorine gas is in excess
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its because chlorine gas is in excess
I wouldn't quite go that far.
Consider for instance the reaction between stilbene (PhCH=CHPh) and Br2. Even if the bromine is in a large excess, under regular conditions there's very little chance you'll get 1,1,2,2-tetrabromo-1,2-diphenylethane (PhCBr2CBr2Ph).
S