What Are Oxyacids?
Oxyacids are acids formed from hydrogen and polyatomic oxyanions. For example:
- Nitric acid (HNO3) forms from the nitrate ion (NO3−)
- Sulfuric acid (H2SO4) forms from the sulfate ion (SO42−)
- Sulfurous acid (H2SO3) forms from the sulfite ion (SO32−)
Dissociation of Oxyacids in Water
When oxyacids dissolve in water, they dissociate into hydrogen ions (H+) and the corresponding polyatomic ion:
- HNO3 → H+ + NO3−
- H2SO4 → 2H+ + SO42−
Note that the polyatomic ion remains intact; nitrogen and oxygen atoms do not separate individually. The number of hydrogen ions released corresponds to the charge on the polyatomic ion (e.g., sulfate has a charge of -2, so two H+ ions are released).
Naming Patterns of Oxyacids
The naming of oxyacids depends on the suffix of the oxyanion:
- Oxyanions ending with -ite form acids ending with -ous (e.g., nitrite → nitrous acid, sulfite → sulfurous acid)
- Oxyanions ending with -ate form acids ending with -ic (e.g., nitrate → nitric acid, sulfate → sulfuric acid)
Examples:
| Oxyanion | Charge | Acid Name | Acid Formula | |----------|---------|-----------------|--------------| | Nitrite | -1 | Nitrous acid | HNO2 | | Nitrate | -1 | Nitric acid | HNO3 | | Sulfite | -2 | Sulfurous acid | H2SO3 | | Sulfate | -2 | Sulfuric acid | H2SO4 | | Chlorite | -1 | Chlorous acid | HClO2 | | Chlorate | -1 | Chloric acid | HClO3 |
Writing the Formula of Sulfuric Acid
To write the formula for sulfuric acid:
- Identify the cation: hydrogen (H+)
- Identify the anion: sulfate (SO42−)
- Balance charges: two H+ ions balance one SO42− ion
- Write the formula: H2SO4
- Indicate aqueous state: H2SO4 (aq)
This method ensures the total positive and negative charges cancel out.
Additional Notes
- Binary acids (e.g., hydrochloric acid) contain only two elements and start with "hydro" and end with "-ic acid".
- Understanding the relationship between oxyanion suffixes and acid names simplifies memorization.
- Common polyatomic ions and their corresponding acids include acetate → acetic acid and carbonate → carbonic acid.
By recognizing these patterns and practicing formula writing, naming oxyacids becomes straightforward and intuitive.
For a deeper understanding of the underlying concepts, you may find the following resources helpful:
Oxy acid they are formed from oxyanion. This is an oxy acid. Nitric acid is formed from nitrate oxyanion. So sulfate
oxyanion gives us sulfuric acid H2SO4 and sulfite oxyion gives us H2SO3. What we have to understand here is
couple of things. First thing is let's write HNO3 in aquous medium. It will break into its component ions. In this
case H+ and NO3 whole NO3 minus not nitrogen and oxygen here they do not separate that's why I told you at the
beginning those polyatomic ions behave like a group we cannot separate these N and O into ions similarly we can write
H2SO4 in the aquous medium in water you will get hydrogen and sulfate group again
sulfate whole group and here the difference is since there are two hydrogen's in the formula you will get
two hydrogen ions. You can see this number is depend on the charge of the polyatic ion. If the charge is two you
will get two hydrogen's. Charge is one you will get one hydrogen atom. If the charge is three with phosphate is called
phosphoric acid you will get three hydrogen and the phosphate group in water. That's how you dissociate. We
call it dissociate acids in the aquous medium. Now we know oxy acids are formed by
hydrogen and polyatomic ions. Now we are trying to name them. When we name polyatomic ions, there's a pattern. For
example, here we have nitrite and you can see it end with it. Similarly, we have nitrate ending with eight. So
basically what I'm trying to say here is nitrite and nitrate it and eight eight has more oxygen than it for example here
we can see it sulfite and sulfate sulfate has four oxygen and sulfite has three oxygen now let's see when these
ions form oxy acids how can we name them so there is also a pattern for example if you make an acid with a polar atomic
ion that named with I like nitrite. When this nitrite form an oxy acid in this case it would be H N O2 you can see NO2
is single negative H is single positive it cancels out. So this is one acid and with nitrate we will get HNO3.
How can we name them? So when we are naming them if the oxyanion in this case we are talking about nitrite and
nitrate. If the oxyion ending with it that means nitrite let's focus of the acid formed with nitrite then when we
are naming it would be base name of the oxyion in this case base name is like night and you add us o us u s so maybe
this is little hard to do like this it may be much easier sometimes to just remember the name with nitrite it would
be truss n i t r o u s nitrous acid. So it would be H N O2. If the oxy ending with A, we are talking about
nitrate. The acid would be ending with Ike base name and Ike. I would just try to remember it without worrying about
this thing. It would be nitric nitric acid. Important thing is recognizing the pattern. Now we know about polyatomic
ions. It 8 it has less oxygen 8 has more oxygen. sulfide sulfate chloride chlorate like that it will take some
time for you to understand and remember now we know with nitrite we will get nitrous acid nitrate we will get nitric
acid H n3 sulfide you will get sulfurous acid and sulfate you will get sulfuric acid
chloride you will get chlorus acid and chloride you will get chloric acid and us when you understand the name of the
polyatic ion which is an oxyion here then it's much easier to name the acid oxy acid. So it says write the formula
of sulfuric acid. So let's follow the steps. So name of sulfuric acid. When you see the name we definitely know it
is an acid but it does not start with hydro like hydrochloric acid or hydro bromic acid. That mean there is an
polyatomic ion in this acid and also there's ik sulfuric here since I see iick is here the polyatomic ion should
end with eight with the practice you don't even want to know these things you will see that sulfuric start with
sulfate 8 sulfate which is S4 2 minus so the first step is write the symbol for the cation and its charge this is for
ionic compounds even though these acids are not ionic compounds. They behave like in aquous medium. Let's write the
cation and its charge. Cation is always H+ in acids. And next one is write the symbol for the annion and N is charge. I
just told you it is sulfate. We saw how we got sulfate looking at N and 8 and sulf. Then same thing we did so many
times. Charge becomes a subscript. So this goes here and two goes here. It would be H2 SO4. We don't write one
here. If you prefer at the beginning you can put parenthesis so you don't get confused. And also it says add aq for
aquous to indicate dissolved in water aquous. So these compounds become acids in aquous medium. Check that the total
charge of the kion cancels out total charge of the anion. Total charge of the cation is there are two hydrogen's each
hydrogen is + one and there's only one sulfate group each one is -2 you can see two positive ones and 1 -2 cancels out
to each other that means H2SO4 seems correct here we have some name of the oxy acid and they are oxy annions and I
want you to remember this again guys if you understand it's not that hard to remember if it is eight is nitrous
nitrite nitrate gives nitric sulfite gives sulfurous sulfate sulfuric. So acetate acetic and carbonate gives
carbonic acid. Right? Now please understand the pattern when you understand it is not that hard to
remember this. This is a very busy slide but still it is showing all of the nomenclature we did so far. I'm not
going to do that binary acids. We know binary acids have only two elements. It start with hydro and ending with acid.
Whenever it says hydro and end with acid, we know it has only two elements.
Heads up!
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