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Sodium Sulfide Formula – Structure, Properties, Uses, Sample Questions

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  • Last Updated : 28 Apr, 2022

Sodium sulphide, or Na2S, is an inorganic chemical compound with the formula Na2S that has risen to prominence in the organic chemical industry. It’s a powerful alkaline solution that smells like rotten eggs when exposed to moist air. Despite the fact that the solid-state is yellow, the solution is colorless. It’s usually labeled as “sodium sulphide flakes” in the grades.

What is Sodium sulphide?

Sodium sulphide is a salt that is important in the organic chemistry sector. The chemical formula for sodium sulphide is Na2S, or its hydrate, Na2S9H2O. Anhydrous and hydrous salts are both colorless solids. Sodium sulphide is a water-soluble alkaline chemical with a strongly acidic solution. 

When Na2S and its hydrates are exposed to damp air, hydrogen sulphide is produced. This discharge has a rotten egg odour. Sodium sulphide in solution has a yellow solid form and is sold in grades known as sodium sulphide flakes. Disodium sulphide is the IUPAC designation for sodium sulphide. Sodium sulphide has an oxidation number of -2, and its pH is 10.4.

Structure of Sodium Sulphide

The antifluorite structure is adopted by Na2S. This structure is created by swapping anions and cations’ locations. This means that the fluoride sites are occupied by Na+, whereas the Ca2+ sites are occupied by S2-.

Sodium Sulphide

Properties of Sodium Sulfide

Physical Properties

Chemical Formula



1.86 gm/cm3

Molar Mass

78.0452 g/mol

Autoignition temperature

> 480 °C (896 °F; 753 K)

Melting Point

1,176° C (2,149° F)


 Odor of rotten eggs


 Anhydrous yellow crystalline solids

Oxidation Number





Insoluble in ether; slightly soluble in alcohol

Chemical Properties

  • In water, sodium sulphide dissolves and creates the ions it requires.

Na2S + H2O → 2Na+ + HS + OH

  • It readily oxidized when heated, producing sodium carbonate and sulphur dioxide.

2Na2S + 3O2 + 2CO2 → 2Na2CO3 + 2SO2

  • When it interacts with sulphur, polysulfides are generated.

2Na2S + S8 → 2Na2S5

  • Sodium sulphide is converted to sodium sulphate when it is oxidized by hydrogen peroxide.

Na2S + 4 H2O2 → 4 H2O + Na2SO4

Uses of Sodium Sulfide

  1. It’s utilized in the kraft process in the paper and pulp industry.
  2. It’s employed as an oxygen scavenger in water treatment.
  3. It is utilised as a bleaching agent in the textile industry.
  4. Sodium sulphide is primarily utilised in the kraft process in the pulp and paper industries. When wood is transformed into wood pulp using the kraft process, sodium hydroxide and sodium sulphide are used to break down the lignin in the wood fiber.
  5. This substance is utilized in the treatment of water. Sodium sulphide is used as an oxygen scavenger in this approach.
  6. To tone black and white photos in chemical photography, sodium sulphide is utilized as a metal precipitant.
  7. Sodium sulphide is employed as a bleaching, dechlorinating, and desulphurizing chemical in the textile business.
  8. Sulfur dyes and other chemical compounds are utilized in the manufacturing of rubber chemicals.
  9. Ore flotation, dyeing, oil recovery, and detergent are just a few of the applications.

Sample Questions

Question 1: Is Sodium Sulphide soluble in water?


Sodium is a group one element, and all group one elements are soluble in water, including sodium sulphide. Although sodium sulphide is very soluble, its solubility is temperature dependent. It is mildly soluble in alcohol but insoluble in ethers.

Another factor that contributes to sodium sulfide’s water solubility is that it is an ionic molecule that tends to dissociate its ions in water. Water dissolves roughly 12.4g/100 mL at 0°C. Sodium sulphide is only 18.6 g/100 mL soluble in water at 20°C. Furthermore, to make sodium sulphide soluble at 39g/100mL, 50°C is required for hydrolysis.

Question 2: How to make Sodium Sulphide?


The salt can be made in the lab by reducing sulphur with sodium in anhydrous ammonia or by reducing sodium in dry THF with a catalytic quantity of naphthalene.

2 Na + S → Na2S

Question 3: Is Sulphate of Sodium an electrolyte?


Sodium sulphate anhydrous is the sodium salt of sulfuric acid. In isosmotic solutions, an electrolyte replenisher called sodium sulphate anhydrous is employed to guarantee that distribution does not disrupt normal electrolyte balance or induce water and ion absorption or excretion. 

The high melting point of sodium sulphide is due to the strong electrostatic interactions between sulphide molecules and sodium ions.

Question 4: What is the purpose of Sodium Sulphide?


Sodium sulphide is largely utilised in the craft process of the pulp and paper industry. It improves the sulphate cooking process’ selectivity and speeds up the delignification process. It’s used as a bleaching agent in the textile business and to preserve developer solutions against oxidation in the photographic industry.

Question 5: What will happen when Sodium Sulphide interacts with Sulphur?


Polysulfides are formed when sodium sulfide interacts with sulphur.

2Na2S + S8 → 2Na2S5

Question 6: What will happen when sodium sulfide is oxidized?


When heated, it easily oxidised, creating sodium carbonate and sulphur dioxide.

2Na2S + 3O2 + 2CO2 → 2Na2CO3 + 2SO2

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