Acids, Bases, and SALTS. According to Arrhenius theory, Acid + base salt + water Examples: HCl + NaOH NaCl + H 2 O H 2 SO 4 + Sr(OH) 2 SrSO 4 + 2H 2 O. SALTS ~ Defined. A salt is an ionic compound with a metallic cation and an monatomic or polyatomic anion.
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According to Arrhenius theory,
Acid + base salt + water
HCl + NaOH NaCl + H2O
H2SO4 + Sr(OH)2 SrSO4 + 2H2O
There are six strong acids~
HCl, HBr, HI, H2SO4, HNO3 HClO4
There are six strong bases~
LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2,Ba(OH)2
All other acids and bases are considered weak and do NOT dissociate completely.
Therefore when an acid and base are combined the final pH will depend on which of the reactants is strong or weak.
Strong acid + strong base neutral salt + H2O
The acid and base will neutralize each other and create a solution with pH 7.
Strong acid + weak base salt and water (pH < 7)
Because the weak base doesn’t completely dissociate, the H1+ ions will prevail in determining pH.
Weak acid and strong base salt and water (pH> 7)
Because the weak acid doesn’t completely dissociate, the OH1- ions will prevail in determining pH.
You would think that putting a salt in water would have nothing to do with acids or bases and pH, but that is NOT the case.
NaCl + H2O H1+(aq) + Cl1-(aq) + Na1+(aq) + OH1-(aq)
The hydrogen from the strong acid and the hydroxide from the strong base neutralize each other. Here the pH is 7.
NH4Cl +H2O NH4OH(aq) + H1+(aq) + Cl1-(aq)
Notice that the product is a strong acid (which completely dissociates) and a weak base (which does NOT completely dissociate). Therefore, the strong acid is the prevailing ionic species and influences the pH.
The pH will < pH7.
The opposite will be true when the salt is derived from a weak acid and a weak base. The pH will be > pH7.
If a salt derived from both a weak acid and weak base (Ex. FeC2O4)is put in water the pH will depend on which was weaker.
There is also another class of salts called acidic and basic. They will also affect pH values.
These salts occur when there is NOT complete neutralization of the acid or base.
Acidic salt ~ NaHSO4
(incomplete neutralization of sulfuric acid)
Basic salt ~ BaOHCl
(incomplete neutralization of barium hydroxide)