Acid salt

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Template:Short description Template:Use dmy dates Acid salts are a class of salts that produce an acidic solution after being dissolved in a solvent. Its formation as a substance has a greater electrical conductivity than that of the pure solvent.[1] An acidic solution formed by acid salt is made during partial neutralization of diprotic or polyprotic acids. A half-neutralization occurs due to the remaining of replaceable hydrogen atoms from the partial dissociation of weak acids that have not been reacted with hydroxide ions (Template:Chem2) to create water molecules.

Formation

Structure of ammonium chloride

Acid–base property of the resulting solution from a neutralization reaction depends on the remaining salt products. A salt containing reactive cations undergo hydrolysis by which they react with water molecules, causing deprotonation of the conjugate acids.

For example, the acid salt ammonium chloride is the main species formed upon the half neutralization of ammonia in aqueous solution of hydrogen chloride:[2]

Template:Chem2

Examples of acid salts

Example of acid salts
Name Sodium bisulfate Monosodium phosphate Disodium phosphate
Structural formula
Chemical formula Template:Chem2 Template:Chem2 Template:Chem2
IUPAC name Sodium hydrogen sulfate Sodium dihydrogen phosphate Disodium hydrogen phosphate
Other name Template:Unbulleted list Template:Unbulleted list Template:Unbulleted list
Molecular weight Template:Val Template:Val Template:Val
Formal charge zero zero zero
Odour Odourless Odourless Odourless[3]
Appearance White crystals or granules White crystalline powder[4] White, hygroscopic powder[5]
Structure Template:Unbulleted list Monoclinic crystals[6] Monoclinic crystals (anhydrous)[7]
Solubility Template:Unbulleted list Template:Unbulleted list Template:Unbulleted list
Density
 Template:Unbulleted list Template:Val Template:Val
Decomposition

(through heating)

Emits toxic fumes of phosphoxides and sodium oxide[8] Emits toxic fumes of phosphorus- and sodium oxides[8]
Uses Template:Unbulleted list Template:Unbulleted list Template:Unbulleted list

Use in food

Acid salts are often used in foods as part of leavening agents. In this context, the acid salts are referred to as "leavening acids."[9] Common leavening acids include cream of tartar and monocalcium phosphate.

An acid salt can be mixed with certain base salt (such as sodium bicarbonate or baking soda) to create baking powders which release carbon dioxide.[10] Leavening agents can be slow-acting (e.g. sodium aluminum phosphate) which react when heated, or fast-acting (e.g., cream of tartar) which react immediately at low temperatures. Double-acting baking powders contain both slow- and fast-acting leavening agents and react at low and high temperatures to provide leavening rising throughout the baking process.[11]

Disodium phosphate, Template:Chem2, is used in foods and monosodium phosphate, Template:Chem2, is used in animal feed, toothpaste and evaporated milk.

Intensity of acid

An acid with higher [[Acid dissociation constant|Template:Mvar]] value dominates the chemical reaction. It serves as a better contributor of protons (Template:Chem2). A comparison between the Template:Mvar and [[Base dissociation constant|Template:Mvar]] indicates the acid–base property of the resulting solution by which:

  1. The solution is acidic if Template:Math. It contains a greater concentration of Template:Chem2 ions than concentration of Template:Chem2 ions due more extensive cation hydrolysis compared to that of anion hydrolysis.
  2. The solution is alkaline if Template:Math. Anions hydrolyze more than cations, causing an exceeding concentration of Template:Chem2 ions.
  3. The solution is expected to be neutral only when Template:Math.[12]

Other possible factors that could vary pH level of a solution are the relevant equilibrium constants and the additional amounts of any base or acid.

For example, in ammonium chloride solution, Template:Chem2 is the main influence for acidic solution. It has greater Template:Mvar value compared to that of water molecules; Template:Mvar of Template:Chem2 is Template:Val, and Template:Mvar of Template:Chem2 is Template:Val. This ensures its deprotonation when reacting with water, and is responsible for the pH below 7 at room temperature. Template:Chem2 will have no affinity for Template:Chem2 nor tendency to hydrolyze, as its Template:Mvar value is very low (Template:Mvar of Template:Chem2 is Template:Val).[13]

Hydrolysis of ammonium at room temperature produces:

NHA4A+A(aq) +HA2OA(aq)↽−−⇀NHA3A(aq) +HA3OA+A(aq)
Ka=[NH3][H3O+][NH4+]=KwKb
Ka=[1.0×10−14][1.8×10−5]=5.6×10−10

See also

References

Template:Reflist

  1. ↑ Template:Cite journal
  2. ↑ Template:Cite book
  3. ↑ U.S. Coast Guard, Department of Transportation. CHRIS - Hazardous Chemical Data. Volume II. Washington, D.C.: U.S. Government Printing Office, 1984-5.
  4. ↑ Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 15th Edition. John Wiley & Sons, Inc. New York, NY 2007., p. 1153
  5. ↑ Lide, D.R. CRC Handbook of Chemistry and Physics 88TH Edition 2007-2008. CRC Press, Taylor & Francis, Boca Raton, Florida 2007, p. 4-90
  6. ↑ Haynes, W.M. (ed.). CRC Handbook of Chemistry and Physics. 95th Edition. CRC Press LLC, Boca Raton: FL 2014-2015, p. 4-89
  7. ↑ Template:Cite journal
  8. ↑ 8.0 8.1 Template:Cite book
  9. ↑ Template:Cite web
  10. ↑ Template:Cite web
  11. ↑ Template:Cite journal
  12. ↑ Template:Cite book
  13. ↑ Lower, S.K., (1999). Introduction to acid-base chemistry. Chem1 General Chemistry Text. Retrieved from http://www.chem1.com/acad/pdf/c1xacid1.pdf
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