Acid base Question (1 Viewer)
- Thread starter cutemouse
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Pwnage101
Moderator
this isnt too bad
well, going on the Bronsted-Lowryd efinition of acid-base reaction (proton transfer), since a H+ (a proton) is being accepted by the base, a bond is forming between one of teh atoms in the base and teh H+. But teh H+ has no electrons, and since it will be a covalent bond, and not an ionic bond, a co-ordinate bond will have to form, as the base will have to supply bothe electrons that will form the.
Easiest way to see it is OH- - draw a lewis dot diagram, and you'll get something like:
H
' '
: o :
' '
(sorry the diagrams sorta crappy, cause it wont let me start writing on a a new line mid way...)
and ofcours eif you were drawing by hand youd have that in a square brackets with a superscipt of ' ([ DIAGRAM]^-).
Th H+, in a neutralisation/acid-base reaction, would latch onto, say, the bottom lone electron pair of the O atom, and thus a covalent bond will form, but only the O atom supplied electrons.
Try it with NH3+ H+ and tell us if you have any more difficuilty....
well, going on the Bronsted-Lowryd efinition of acid-base reaction (proton transfer), since a H+ (a proton) is being accepted by the base, a bond is forming between one of teh atoms in the base and teh H+. But teh H+ has no electrons, and since it will be a covalent bond, and not an ionic bond, a co-ordinate bond will have to form, as the base will have to supply bothe electrons that will form the.
Easiest way to see it is OH- - draw a lewis dot diagram, and you'll get something like:
H
' '
: o :
' '
(sorry the diagrams sorta crappy, cause it wont let me start writing on a a new line mid way...)
and ofcours eif you were drawing by hand youd have that in a square brackets with a superscipt of ' ([ DIAGRAM]^-).
Th H+, in a neutralisation/acid-base reaction, would latch onto, say, the bottom lone electron pair of the O atom, and thus a covalent bond will form, but only the O atom supplied electrons.
Try it with NH3+ H+ and tell us if you have any more difficuilty....
Hi again,
I researched on the web and I found that this may involve Lewis acids and bases, which I believe is not in the syllabus (taken out in 2001 or 2002 ammendements)... CHEMystery: Acids and Bases: Lewis Acid-Base Reactions
Would I be correct in saying so?
I researched on the web and I found that this may involve Lewis acids and bases, which I believe is not in the syllabus (taken out in 2001 or 2002 ammendements)... CHEMystery: Acids and Bases: Lewis Acid-Base Reactions
Would I be correct in saying so?
Pwnage101
Moderator
technically yes, lewis' definition would be easier to explain with, but B-L definition is fine. i.e. you COULD be asked this questions in the HSC, its realms do NOT fall outside the syllabus
In fact im pretty sure ive seen this querstion in a trial paper....
anyways, dont worry about the drawing, just understand that by defition an base is accepting a PROTON (H+), and when THIS HAPPENS, a bond must form (or else it wouldnt be 'acceptying' it would it?). This bond is covalent, not ionic, its not hard to see that Hbonded with O or N, as it usually is in this case, forms a covalent bond.
But, whats that i hear you ask? H+ has no electrons, so how can it form a bond? Well yes, thats what im saying, a Co-ordiante bond must tehrefore form, beacuse H+ has no electrons to contributed to teh bond, but in order for the bond to form at least 2 electrons are requied. Neitehr of these come from the H+ thsu a co-ordinate bond is fortmed.
EXAMPLES:
H+ + OH-
H+ + NH3
Draw the electron dot diagram for NH3 nad OH- and see how H+ actually bonds to it, ull see that the boind that forms contains 2 electrons, both from the N/O....
In fact im pretty sure ive seen this querstion in a trial paper....
anyways, dont worry about the drawing, just understand that by defition an base is accepting a PROTON (H+), and when THIS HAPPENS, a bond must form (or else it wouldnt be 'acceptying' it would it?). This bond is covalent, not ionic, its not hard to see that Hbonded with O or N, as it usually is in this case, forms a covalent bond.
But, whats that i hear you ask? H+ has no electrons, so how can it form a bond? Well yes, thats what im saying, a Co-ordiante bond must tehrefore form, beacuse H+ has no electrons to contributed to teh bond, but in order for the bond to form at least 2 electrons are requied. Neitehr of these come from the H+ thsu a co-ordinate bond is fortmed.
EXAMPLES:
H+ + OH-
H+ + NH3
Draw the electron dot diagram for NH3 nad OH- and see how H+ actually bonds to it, ull see that the boind that forms contains 2 electrons, both from the N/O....
Pwnage101
Moderator
yes - O atom has 6e, H atom has 1 E, but an extra e makes it a negative ion, resulting in the octet needed. H+ just joins one of the lone pairs.
But it has 1 electron, doesn't it?
Pwnage101
Moderator
H has one electron
H+ does NOT (its an ion...)
thats why when we talk about 'proton donors' we talk about H+ - they are just a proton, with no electron (at least the isotope Hydrogen-1)
Also, OH- has 3 lone pairs
okay see it in pictures:
http://wpcontent.answers.com/wikipedia/commons/4/4d/LewisAcid.png - look at tehe bottom one, this illustrates my point
http://www.chemcool.com/regents/chemicalbonding/aim3.h25.gif - look at the left one only
This is sorta fundamental...
H+ does NOT (its an ion...)
thats why when we talk about 'proton donors' we talk about H+ - they are just a proton, with no electron (at least the isotope Hydrogen-1)
Also, OH- has 3 lone pairs
okay see it in pictures:
http://wpcontent.answers.com/wikipedia/commons/4/4d/LewisAcid.png - look at tehe bottom one, this illustrates my point
http://www.chemcool.com/regents/chemicalbonding/aim3.h25.gif - look at the left one only
This is sorta fundamental...
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kwabon
Banned
pretty sure this is not HSC work, is it???? 
It is...pretty sure this is not HSC work, is it????
Pwnage101
Moderator
I dont understand what the problem is?
U learn how to draw lews dot diagrams in year 11, and you have to do it in the ozone chapter in Topic 3 of the HSC course - so yes u need to know that.
Also, in that same ozone chapter of topic 3, u are required to learn what a co-ordinate covalent bond is, so yes it is in the HSC course.
In topic 2 u learn a base is a proton acceptor.
This question is therefore well within the scope of the HSC and, to be honest, very easy (wouldnt be worth more than 2 marks).
i dont see what the problem is, and i cant think of a better way of explaining it than i already have, for only 2 marks....
So to recap one last time
for H3O+ + OH- -> 2H20
clearly this is a proton transfer/ acid/base reaction.
draw the electron dot diagrma for each of the reactants.
then draw the electron dot diagram for the product (draw the 2 molecules of water separat). Notice how u get one water molecule by the H+ being removed from the hydronium ion. And the secon one comes when this H+ ion attaches itself to OH-. The bond that is formed here is a COVALENT (Since it is between H and O) CO-ORDINATE (since only the O is supplying the electrons, H+ has NO ELECTRONS - This is a fairly absic idea...) BOND.
Done.
Do this for ammonia + water
U learn how to draw lews dot diagrams in year 11, and you have to do it in the ozone chapter in Topic 3 of the HSC course - so yes u need to know that.
Also, in that same ozone chapter of topic 3, u are required to learn what a co-ordinate covalent bond is, so yes it is in the HSC course.
In topic 2 u learn a base is a proton acceptor.
This question is therefore well within the scope of the HSC and, to be honest, very easy (wouldnt be worth more than 2 marks).
i dont see what the problem is, and i cant think of a better way of explaining it than i already have, for only 2 marks....
So to recap one last time
for H3O+ + OH- -> 2H20
clearly this is a proton transfer/ acid/base reaction.
draw the electron dot diagrma for each of the reactants.
then draw the electron dot diagram for the product (draw the 2 molecules of water separat). Notice how u get one water molecule by the H+ being removed from the hydronium ion. And the secon one comes when this H+ ion attaches itself to OH-. The bond that is formed here is a COVALENT (Since it is between H and O) CO-ORDINATE (since only the O is supplying the electrons, H+ has NO ELECTRONS - This is a fairly absic idea...) BOND.
Done.
Do this for ammonia + water
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