Sodium Bisulphate: Structure, Properties, Preparation & Uses

Sodium bisulfate, also known as sodium hydrogen sulfate, is the sodium salt of the bisulfate anion, with the molecular formula NaHSO₄. It is an acid salt formed by partial neutralization of sulfuric acid by an equivalent of sodium base, typically in the form of either sodium hydroxide or sodium chloride. It is a dry acid in crystal, granular, or powder form. Solutions of sodium bisulfate are acidic, with a 1M solution having a pH of slightly below 1.

Sodium bisulfate may also be called sodium hydrogen sulfate, sulfuric acid, monosodium salts, sodium acid sulfate, sodium hydrosulfate, or sodium hydrogen sulfate. 


Sodium bisulfate, with the chemical formula NaHSO4, consists of sodium (Na+), hydrogen (H+), sulfur (S), and oxygen (O) atoms. Its structure can be described in terms of its molecular and crystal structure.

Molecular Structure

  • It has a simple molecular structure consisting of one sodium ion (Na+), one hydrogen ion (H+), and one bisulfate ion (HSO4-).
  • The bisulfate ion (HSO4-) is a polyatomic ion composed of one hydrogen atom (H), one sulfur atom (S), and four oxygen atoms (O). It carries a net charge of -1.

Crystal Structure

  • It forms as white, crystalline powder.
  • In its crystalline form, sodium bisulfate forms a lattice structure, where the sodium ions (Na+) and bisulfate ions (HSO4-) arrange themselves in a repeating pattern throughout the crystal lattice.
  • The arrangement of ions in the crystal lattice is such that each sodium ion is surrounded by bisulfate ions and vice versa, with electrostatic forces holding the ions together.

Chemical Bonds

  • Ionic bonds: The bonding between sodium and bisulfate ions is ionic in nature. Sodium, being a metal, donates an electron to the bisulfate ion, resulting in the formation of positively charged sodium ions (Na+) and negatively charged bisulfate ions (HSO4-).
  • Covalent bonds: Within the bisulfate ion (HSO4-), there are covalent bonds between the hydrogen, sulfur, and oxygen atoms. These covalent bonds involve the sharing of electrons between atoms.

Physical Properties of Sodium bisulfate

  • Appearance: White, crystalline powder
  • Odor: Generally odorless
  • Density: 2.742 g/cm³ (at 20°C)
  • Melting Point: Decomposes at approximately 315°C (decomposition begins at around 150°C)
  • Solubility: Soluble in water, with a solubility of approximately 55.4 g/100 mL at 20°C. Insoluble in most organic solvents.
  • Hygroscopicity: Absorbs moisture from the air
  • pH: Highly acidic, typically around pH 1 in aqueous solution
  • Stability: Stable under normal conditions but decomposes upon heating or exposure to strong acids.

Hazardous Properties

  • Irritant to skin, eyes, and respiratory system
  • May cause burns upon prolonged contact with skin or eyes
  • Generates heat upon dissolution in water

Chemical properties of Sodium bisulfate

Acidic Nature: Sodium bisulfate is a strong acid, dissociating in water to release hydrogen ions (H⁺) and bisulfate ions (HSO₄⁻).

Reaction with Bases: Reacts vigorously with bases to form salts and water. For example:

  • NaHSO₄ + NaOH → Na₂SO₄ + H₂O

Reaction with Metals: Can react with certain metals, particularly reactive metals like aluminum and zinc, to produce hydrogen gas and the corresponding metal sulfate. For example:

  • 2 NaHSO₄ + 3 Zn → ZnSO₄ + Na₂SO₄ + H₂↑

Decomposition: Decomposes upon heating, releasing sulfur dioxide (SO₂), oxygen (O₂), and water (H₂O). The decomposition starts around 150°C, with complete decomposition occurring around 315°C. For example:

  • 2 NaHSO₄ → Na₂SO₄ + SO₂↑ + H₂O

Reaction with Carbonates and Bicarbonates: Reacts with carbonates (CO₃²⁻) and bicarbonates (HCO₃⁻) to release carbon dioxide (CO₂), water, and the corresponding salt. For example:

  • NaHSO₄ + NaHCO₃ → Na₂SO₄ + CO₂↑ + H₂O

Oxidation-Reduction Reactions: Can participate in oxidation-reduction reactions, particularly as an oxidizing agent in certain contexts.

Preparation of Sodium bisulfate

It can be prepared through several methods, but the common one involves the reaction of sodium hydroxide (NaOH) with sulfuric acid (H2SO4) or sodium sulfate (Na2SO4).

Direct Neutralization:

  • Sodium bisulfate can be produced by the direct neutralization of sulfuric acid with sodium hydroxide.
  • The chemical equation for this reaction is: H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
  • The resulting sodium sulfate (Na2SO4) is further reacted with additional sulfuric acid to yield sodium bisulfate: Na2SO4 + H2SO4 → 2 NaHSO4

Reaction of Sodium Carbonate with Sulfuric Acid:

  • Sodium carbonate (Na2CO3) reacts with sulfuric acid to form sodium sulfate and carbon dioxide gas. The sodium sulfate obtained can then be converted to sodium bisulfate by reacting it with additional sulfuric acid.
  • The chemical equation for the initial reaction is: Na2CO3 + H2SO4 → Na2SO4 + CO2 + H2O
  • The sodium sulfate produced can be further reacted with sulfuric acid as shown previously.

Reaction of Sodium Hydroxide with Sulfur Dioxide:

  • Sodium hydroxide (NaOH) reacts with sulfur dioxide (SO2) to form sodium bisulfite (NaHSO3), which can be converted to sodium bisulfate by further reaction with sulfuric acid.
  • The chemical equation for the initial reaction is: NaOH + SO2 → NaHSO3
  • The sodium bisulfite obtained can be oxidized to sodium bisulfate by reaction with sulfuric acid: NaHSO3 + H2SO4 → NaHSO4 + H2O

Indirect Methods:

  • Sodium bisulfate can also be produced indirectly from sodium sulfate through reaction with sulfuric acid, as shown in the direct neutralization method.

Uses of Sodium bisulfate

  • It is commonly used as an acidic pH adjuster in various industries, such as in swimming pools to lower pH levels and in water treatment to neutralize alkaline water.
  • It is used in household cleaning products as a descaler or acid cleaner to remove scale and stains from surfaces, such as metal, tile, and porcelain.
  • In the food industry, it is used as a food additive, particularly as an acidulant and preservative in processed foods.
  • It is used in textile dyeing and printing processes as a pH regulator and mordant.
  • It may be found in personal care products such as hair dyes and hair removal creams.
  • It can be used for dechlorination of water, effectively neutralizing chlorine compounds.
  • It finds application as a laboratory reagent in chemical synthesis, particularly in reactions requiring an acidic environment.
  • In industrial processes, sodium bisulfate is used for metal surface treatment, electroplating, and as a chemical intermediate in the production of various compounds.