I read somewhere that salts which do not contain a replaceable hydrogen or hydroxyl group are classified as normal salts. But I also know that strong base-weak acid salts are basic in nature.
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2 Answers
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Normal salts do not have to be neutral, and vice versa. There are two different features of a salt: (1) containing a replaceable hydrogen, and (2) making an acidic solution in water. They are not necessarily related. For example:
- $\ce{NaHSO4}$ has both.
- $\ce{NaHCO3}$ has the first and not the second (in fact, being a salt of a strong base and a weak acid, it has to be basic in nature, as you correctly recall).
- On the other hand, $\ce{CuSO4}$ is partially hydrolyzed in water solution and hence has the second feature, but not the first.
- To make the picture complete, $\ce{NaCl}$ has neither.
Likewise, the opposite features of (1) having a hydroxy group and (2) making a basic solution in water are even less related. For example:
- $\ce{Cu2(OH)2CO3}$ has the first feature, but not the second (for it is not even soluble in water).
- $\ce{CH3COONa}$ is partially hydrolyzed in water solution and hence has the second feature, but not the first.
- $\ce{MgCl2}$ and $\ce{Mg(OH)2}$ form several basic salt phases with both features (J. Chem. Eng. Data 2017, 62 (4), 1384–1396). They are only sparingly soluble but still form measurably alkaline solutions, especially when warmed.
- $\ce{MgSO4}$ has neither.
answered May 13, 2018 at 13:35
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$\begingroup$ What about the particular case in the question? $\endgroup$– A JCommented May 13, 2018 at 13:45
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2$\begingroup$ Sodium acetate is hidden somewhere in my answer. $\endgroup$ Commented May 13, 2018 at 13:46
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$\begingroup$ Okay so I get it...a salt is only neutral when it follows neither 1 not 2. Thanks :) $\endgroup$– A JCommented May 13, 2018 at 13:52
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2$\begingroup$ No, a salt is neutral when it doesn't follow 2, and normal when it doesn't follow 1. These things may or may not coincide. $\endgroup$ Commented May 13, 2018 at 13:54
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2$\begingroup$ Well, then chemistry is hard. Now to the point: sulfate ion does not hydrolyze in water, since it is a very weak base, like you said. As for the acetate ion and its basicity: without knowing the pKa of acetic acid, you wouldn't know that. $\endgroup$ Commented May 13, 2018 at 22:11
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Since sodium acetate is the salt formed from sodium hydroxide (a strong base) and acetic acid (a weak acid) a solution of the salt should be alkaline.
