Chapter 3
Ionic compounds
3.11 H+ and OH- Ions: An Introduction to Acids & Bases
Acids and Bases
Two of the most important ions we will study are
the hydrogen ion: H+
and
the hydroxide ion: OH-_____ ions.
A hydrogen ion is simply a proton.
When acids dissolve in water, the proton can attach to a water molecule
to form a hydronium ion.
H+ + H2O → H3O+
Chemists use hydrogen and hydronium ions interchangeably in water
solutions.
Acid – A substance that provides H+ ions in water.
(e.g. HCl, HNO3, H2SO4, H3PO4 are among the most common.)
Base – A substance that provides OH- ions in water.
(e.g. NaOH, KOH, Ba(OH)2, Ca(OH)2, and NH4OH are among the most
common.)
Naming acids.
The name of the acid depends on the type of anion present.
Case 1: If the anion contains no oxygen atoms, the acid is named by
adding a prefix of hydro to the name of the anion, changing the
ending to ic, and adding the word acid.
HCl
hydrochloric acid
HF
hydrofluoric acid
HBr
hydrobromic acid
HCN hydrocyanic acid
HI
hydroiodic acid
H 2S
Chapter 3 Page 1 of 6
hydrosulfuric acid
Case 2: If the anion contains oxygen atoms, the acid is named based on
the varying number of O atoms.
There is a series of “base” anions that you must memorize. These
anions all end in “ate”. The acids made by adding enough H atoms to
get a neutral compound are named by changing the “ate” to “ic” and
adding the work acid.
Convert the “base” oxyanion that we learned earlier to their
corresponding acids.
Practice: write formulas & names for the acids made from the
following polyatomic ions:
• NO3-
nitrate ion
.
HNO3 nitric acid
• CO32-
carbonate ion
.
H2CO3 carbonic acid
• ClO3-
chlorate ion
.
HClO3 chloric acid
• BrO3-
bromate ion
.
HBrO3 bromic acid
• SO42-
sulfate ion
.
H2SO4 sulfuric acid
• PO43-
phosphate ion
.
H3PO4 phosphoric acid
Acids can also be made from the series of oxyanions.
For the name, change “ate” to “ic or “ite” to “ous”
and add the word acid.
Ion Formula
Ion Name
Acid Formula
Acid Name
− ClO4-
perchlorate ion
HClO4
perchloric acid
− ClO3-
chlorate ion
HClO3
chloric acid
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− ClO2-
chlorite
HClO2
clorous acid
− ClO-
hypochlorite
HClO
hypochlorous acid
− BrO4-
perbromate ion
HBrO4
perbromic acid
− BrO3-
bromate ion
HBrO3
bromic acid
− BrO2-
bromite
HBrO2
bromous acid
− BrO-
hypobromite
HBrO
hypobromous acid
− IO4-
periodate ion
HIO4
periodic acid
− IO3-
iodate ion
HIO3
iodic acid
− IO2-
iodite
HIO2
iodous acid
− IO-
hypoiodite
HIO
hypoiodous acid
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Protic Nature of Acids.
Different acids can provide different numbers of H+ ions per acid
molecule.
– Hydrochloric acid, HCl, provides one H+ ion per acid
molecule. (
monoprotic
)
– Sulfuric acid, H2SO4, can provide two H+ ions per acid
diprotic
)
molecule. (
– Phosphoric acid, H3PO4, can provide three H+ ions per acid
molecule. (
triprotic
)
Diprotic and triprotic can be grouped together as polyprotic acids.
Bases.
• Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are
bases.
• When these compounds dissolve, OH– anions go into solution
along with the metal cation.
• Different bases can provide different numbers of OH– ions per
formula unit.
– Sodium hydroxide (NaOH) provides
OH– ion per formula unit.
– Barium hydroxide, Ba(OH)2 can provides
OH– ions per formula unit.
End of Chapter
Chapter 3 Page 4 of 6
one
.
two
.
Oxyacid/Oxyanion Memory Framework
Inorganic nomenclature would be a lot simpler if it weren’t for the oxyacids and
the oxyanions they form. An acid that contains oxygen in addition to hydrogen
and another nonmetal is an oxyacid. When hydrogen ions are removed from an
oxyacid, the oxygen stays with the nonmetal as part of an oxyanion Here’s a few
matrices I hope will help you in remembering how they go together and are named.
Once you’ve mastered this you will be able to name 23 oxyacids and the associated
ion.
Remember these seven “ic” acids:
Acid (Group)
Carbonic acid (4A)
Nitric acid (5A)
Phosphoric acid (5A)
Sulfuric acid (6A)
Chloric acid (7A)
Bromic acid (7A)
Iodic acid (7A)
Formation Equation
+
H2CO3 2H + CO32HNO3 H+ + NO3H3PO4 3H+ + PO43H2SO4 2H+ + SO42HClO3 H+ + ClO3HBrO3 H+ + BrO3HIO3 H+ + IO3-
Ion Name
Carbonate
Nitrate
Phosphate
Sulfate
Chlorate
Bromate
Iodate
Got that down? Notice that there are five ions with three oxygens and two ions
with four oxygens, so the ic/ate relationship for naming oxyacids/oxyanions
doesn’t relate to the same number of oxygens (How ‘bout the charge number?).
Now, let’s look at the cousins of these “ic” acids. The most complicated first,
those formed by the Group 7A elements Cl, Br, and I (excluding fluorine).
Number of Oxygen
Atoms Compared with
–ic acid and –ate
Anion
Acid Prefix and/or
suffix (Example)
Anion Prefix and/or
Suffix(Example)
One more
HClO4
Same
HClO3
One fewer
HClO2
Two fewer
HClO
No Oxygen
HCl
Per-ic
(perchloric)
ic
chloric
-ous
chlorous
Hypo-ous
hypochlorous
Hydro-ic
hydrochloric
Per-ate
ClO4- Perchlorate
-ate
ClO3- chlorate
-ite
ClO2- chlorite
hypo-ite
ClO- hypochlorite
-ide
Cl- chloride
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Other “ic” acids and anions and how they are arrayed on the periodic table.
4A/14
H2CO3/CO32Carbonic/
Carbonate
5A/15
HNO3/NO3Nitric/nitrate
HNO2/NO2Nitrous/nitrite
H3PO4/PO43Phosphoric/
Phosphate
H3PO3/PO33Phosphorous/
Phosphite
6A/16
7A/17
H2SO4/ SO42Sulfuric/sulfate
HClO4 / ClO4perchloric/perchlorate
H2SO3/ SO32Sulfurous/sulfite
HClO3 / ClO3chloric/chlorate
H2S/S2Hydrosulfuric/sulfide
HClO2 / ClO2chlorous/chlorite
HClO / ClOhypochlorous/hypochlorite
HCl
hydrochloric/chloride
HBrO4 BrO4perbromic/perbromate
HBrO3 / BrO3bromic/bromate
HBrO2 / BrO2bromous/bromite
HBrO / BrOhypobromous/hypobromite
HBr
hydrobromic/bromide
HIO4 IO4-periodic/periodate
HIO3 / IO3iodic/iodate
HIO2 / IO2iodous/iodite
HIO / IOhypoiodous/hypoiodite
HI
hydroiodic/iodide
Other acids you should know:
H2C2O4
HCN
H2S
HC2H3O2
oxalic acid
hydrocyanic acid
hydrosulfuric acid
acetic acid
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