Acid - base pairs.
Arrhenius theory, says, that acids are substances that dissociate in water to yield electrically charged atoms or molecules, called ions, one of which is a hydrogen ion (H+), and that bases ionize in water to yield hydroxide ions (OH−).
It is now known that the hydrogen ion cannot exist alone in water solution; rather, it exists in a combined state with a water molecule, as the hydronium ion (H3O+). In practice the hydronium ion is still customarily referred to as the hydrogen ion.
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a) HClO3 + H2O <=> H3O + + ClO3-
HClO3 is the acid, ClO3- is the base (acid-base pair)
H2O acepts that H+ from the HClO3, and becomes H3O+
H2O is a base, H3O+ is the acid (acid-base pair)
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b) HSeO4 - + NH3 <=> NH4 + + SeO4 2-
Here HSeO4 - can free one H so it would be the acid, and SeO4 2- is the base.
NH3 receives H+ from acid, so it is the base, and NH4+ is the acid.
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c) HCO3- + OH - <=> CO3 2- + H2O
HCO3- gives away one H, so it is the acid, and CO3 2- is the base
(HCO3-,CO3 2-) acid-base pair.
OH- receives the H+ and becomes H2O. OH- is the base and H2O acid.
H2O can be acid and base, remember that. In this case it is the acid.
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d) C5H5NH + + H2O <=> C5H5N- + H3O+
C5H5NH has the H, but on the right it doesn't, so it would be th acid. C5H5N- is the base.
H2O here is a base, because it receives the H+, and becomes H3O+ (the acid).
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