Are Sulfate Salts Acidic or Basic?

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In summary, according to Wikipedia, (NH4)2SO4 and Al2(SO4)3 are acidic, while the other salts do not have a clear classification. However, based on the properties of the ions present in the solution, it is theorized that most of these salts would have a slightly basic pH.
  • #1
michaelxavier
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Are Li2SO4, Na2SO4, K2SO4, Ag2SO4, (NH4)2SO4, MgSO4, BaSO4, COSO4, CuSO4, ZnSO4, SrSO4, Al2(SO4)3, and Fe2(SO4)3 acidic or basic?

On the one hand, Wikipedia says that (NH4)2SO4 and Al2(SO4)3 are acidic, and says nothing about the others. On the other hand logic seems to dictate that in a soluble salt, the SO42- would want to grab H+, leaving OH- floating around to basify the waters.

Thanks!
 
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  • #2
When you dissolve salt, anion is not the only ion present in the solution.

SO42- is a verrrry weak base (something like Kb=10-12). Theoretical pH of 0.1M potassium (or sodium) sulfate is few tenths of the pH unit above 7.

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  • #3
NH4+ is more acidic than SO42- is basic, so (NH4)2SO4 is acidic.

As for Al2(SO4)3, Al3+ is an acidic cation, in that it forms complexes with the water molecules such that the H-atoms is pointing outwards. Because of the polarity of the O-H bond, the H-atoms are somewhat like H+-ions. SO42- is all in all a very weak base, so Al3+ is easily a stronger acid and wins this battle, so Al2(SO4)3 is acidic.

Whether a salt is acidic or basic depends on the acid/base constants for both ions.
 

1. What are sulfate salts?

Sulfate salts are compounds made up of a positively charged ion (cation) and a negatively charged sulfate ion (SO4), such as sodium sulfate (Na2SO4) or calcium sulfate (CaSO4).

2. Are sulfate salts acidic or basic?

The acidity or basicity of sulfate salts depends on the nature of the cation. Generally, sulfate salts of Group 1 and 2 metals (such as sodium or calcium) are basic, while those of transition metals (such as iron or copper) can be either acidic or basic.

3. How do sulfate salts affect the pH of a solution?

Sulfate salts can affect the pH of a solution depending on their acidity or basicity. In general, basic sulfate salts will increase the pH of a solution, while acidic sulfate salts will decrease it.

4. Can sulfate salts be used as acids or bases?

Yes, sulfate salts can be used as acids or bases depending on their composition and the reaction they undergo. For example, sodium sulfate can act as a base when reacting with a strong acid, but as an acid when reacting with a strong base.

5. Are sulfate salts harmful to the environment?

Some sulfate salts can be harmful to the environment, particularly if they are acidic. Acidic sulfate salts can lower the pH of soil or water, making it difficult for plants and aquatic life to survive. However, basic sulfate salts can also cause harm by increasing the pH of water bodies, leading to eutrophication and other environmental issues.

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