Acid salts are a class ofsalts that produce an acidic solution after being dissolved in asolvent. 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 partialneutralization ofdiprotic orpolyprotic acids. Ahalf-neutralization occurs due to the remaining of replaceablehydrogenatoms from the partial dissociation of weak acids that have not been reacted withhydroxide ions (OH⁻) to create water molecules.

Acid–base property of the resulting solution from a neutralization reaction depends on the remaining salt products. A salt containing reactive cations undergohydrolysis by which they react with water molecules, causingdeprotonation of theconjugate acids.

For example, the acid saltammonium chloride is the main species formed upon thehalf neutralization ofammonia inaqueous solution ofhydrogen chloride:^[2]

NH₃(aq) + HCl(aq) → [NH₄]⁺Cl⁻(aq)

Example of acid salts

Name	Sodium bisulfate	Monosodium phosphate	Disodium phosphate
Structural formula
Chemical formula	NaHSO4	NaH2PO4	Na2HPO4
IUPAC name	Sodium hydrogen sulfate	Sodium dihydrogen phosphate	Disodium hydrogen phosphate
Other name	Sodium acid sulfate Bisulfate of soda	Monobasic sodium phosphate Sodium acid phosphate Sodium biphosphate	Disodium hydrogen orthophosphate Sodium phosphate dibasic disodium phosphate
Molecular weight	120.054 g/mol	119.976 g/mol	141.957 g/mol
Formal charge	zero	zero	zero
Odour	Odourless	Odourless	Odourless[3]
Appearance	White crystals or granules	White crystalline powder[4]	White, hygroscopic powder[5]
Structure	triclinic (anhydrous) monoclinic (monohydrate)	Monoclinic crystals[6]	Monoclinic crystals (anhydrous)[7]
Solubility	Soluble in water Insoluble inammonia	Soluble in water Insoluble in ethanol orether	Soluble in water Insoluble in ethanol
Density	2.742 g/cm3 (anhydrous) 1.8 g/cm3 (monohydrate)	0.5–1.2 g/cm3	1.7 g/cm3
Decomposition (through heating)		Emits toxic fumes of phosphoxides and sodium oxide[8]	Emits toxic fumes of phosphorus- and sodium oxides[8]
Uses	Bleaching agents Plating agents and surface treating agents Cleaning and Furnishing Care Products	Treat constipation Clean the bowel before a colonoscopy Bleaching agents	A source of phosphorus Visicol tablets are indicated for cleansing of the colon Corrosion inhibitors and anti-scaling agents

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 includecream of tartar andmonocalcium phosphate.

An acid salt can be mixed with certainbase salt (such as sodium bicarbonate or baking soda) to create baking powders which releasecarbon 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,Na₂HPO₄, is used in foods and monosodium phosphate,NaH₂PO₄, is used in animal feed, toothpaste and evaporated milk.

An acid with higherK_a value dominates the chemical reaction. It serves as a better contributor ofprotons (H⁺). A comparison between theK_a andK_b indicates the acid–base property of the resulting solution by which:

1. The solution is acidic ifK_a >K_b. It contains a greater concentration ofH⁺ ions than concentration ofOH⁻ ions due more extensive cation hydrolysis compared to that of anion hydrolysis.
2. The solution is alkaline ifK_a <K_b. Anions hydrolyze more than cations, causing an exceeding concentration ofOH⁻ ions.
3. The solution is expected to be neutral only whenK_a =K_b.^[12]

Other possible factors that could varypH level of a solution are the relevantequilibrium constants and the additional amounts of any base or acid.

For example, inammonium chloride solution,NH+4 is the main influence for acidic solution. It has greaterK_a value compared to that of water molecules;K_a ofNH+4 is5.6×10⁻¹⁰, andK_w ofH₂O is1.0×10⁻¹⁴. This ensures its deprotonation when reacting with water, and is responsible for the pH below 7 at room temperature.Cl⁻ will have noaffinity forH⁺ nor tendency to hydrolyze, as itsK_b value is very low (K_b ofCl⁻ is7.7×10⁻²¹).^[13]

Hydrolysis of ammonium at room temperature produces:

${\displaystyle K_{\mathrm{a}}=\frac{[\mathrm{N}{\mathrm{H}}_3][{\mathrm{H}}_3{\mathrm{O}}^{+}]}{[\mathrm{N}{\mathrm{H}}_4^{+}]}=\frac{K_{\mathrm{w}}}{K_{\mathrm{b}}}}$

${\displaystyle K_{\mathrm{a}}=\frac{[1.0\times {10}^{-14}]}{[1.8\times {10}^{-5}]}=5.6\times {10}^{-10}}$

• Base salt
• Salt (chemistry)
• Oxoacid
• Sodium bicarbonate
• Sodium bisulfate: an example of acid salt
• Disodium phosphate: an example of acid salt
• Monosodium phosphate: an example of acid salt

• Salts
• Acids

• CS1: long volume value
• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from March 2018