Sodium Sulfide

What Is Sodium Sulfide?

Sodium sulfide is a salt which plays an essential role in the organic chemistry industry. The formula for sodium sulfide is Na2S, or more commonly its hydrate Na2S·9H2O. Both the anhydrous and the hydrous salts are colourless solids. Sodium sulfide is a water-soluble compound, with a strongly alkaline solution. If the compound is exposed in the moist air, Na2S and its hydrates emit hydrogen sulfide. This emission smells like a rotten egg. The solid-state of sodium sulfide in solution is a yellow colour, and it comes as grades, known as sodium sulfide flakes. The IUPAC name of sodium sulfide is disodium sulfide. The oxidation number of sodium sulfide is -2, whereas its pH value is 10.4.

Structure Of Sodium Sulfide 

Na2S adopts the antifluorite structure.  This structure is obtained by exchanging the positions of anions and cations. This means that the Na+ occupy sites of the fluoride and  S2- hold the sites for Ca2+.

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Sodium Sulfide Properties 

Physical Properties of Sodium Sulfide 

Chemical Formula of sodium sulphide


Physical Appearance

Colourless and hygroscopic solid

The odour of sodium sulfide

Rotten eggs


1.856 g/cm3, for  anhydrous

1.58 g/cm3, for pentahydrate

1.43 g/cm3, for nonahydrate

Melting Point of sodium sulfide



Slightly soluble in alcohol, Insoluble in ethers

Molar Mass of sodium sulfide


Bond strength

2/2 = 1


Chemical Properties Of Sodium Sulfide

  • When sodium sulfide is dissolved in water, it forms its corresponding ions. The reaction of the same is given below:

Na2S + H2O → 2Na+ + HS- + OH-

  • Also, sodium sulfide oxidises quickly by heating. The results will be sodium carbonate and sulfur dioxide.

2Na2S + 3O2 + 2CO2 → 2Na2CO3 + 2SO2

  • When sodium sulfide goes under oxidation with hydrogen peroxide, it gives sodium sulfate as a result.

Na2S + 4 H2O2 → 4 H2O + Na2SO4

  • If sodium sulfide is reacted with sulfur, it forms a polysulfide, given as below:

2Na2S + S8 → 2Na2S5


How Is Sodium Sulfide Produced?

In industries, Na2S is produced by a carbothermic reduction reaction. In this reduction reaction, carbon is used as a reducing agent.

Similarly, for sodium sulfide, sodium sulfate is reacted by coal. 

Na2SO4 + 2 C → Na2S + 2 CO2 

In laboratories, the sodium sulfide salt is usually prepared by the reduction method. Sodium sulphur is reacted by anhydride ammonia, or through sodium in dry THF, with the help of naphthalene as a catalyst. The result formed will be sodium naphthalenide. 

2Na + S → Na2S


Sodium Sulfide Uses  

  • Sodium sulfide is mainly used in the pulp and paper industry for the kraft process. As in the kraft process, wood is converted into wood pulp, sodium hydroxide and sodium sulfide help to dissolve the lignin of wood fibre.

  • This compound is used in water treatment. In this method, sodium sulfide acts as an oxygen scavenger agent

  • For chemical photography, sodium sulfide is used as a metal precipitant for toning black and white photographs

  • In the textile industry, sodium sulfide is used as a bleaching agent, dechlorinating agent and also desulphurising agent.

  • In the production of rubber chemicals, sulfur dyes and other chemical compounds are used.

  • Used in various applications like ore flotation, dye-making, oil recovery and detergent. 

Side Effects Of Sodium Sulfide

Sodium sulfide is strongly alkaline. It can cause significant skin burns. Reacting with acid can form hydrogen sulfide, which is a highly toxic and flammable gas. In reduced ventilation spaces, hydrogen sulfide accumulates at the bottom. To use hydrogen sulfide, one should keep the safety data sheet with them.

Na2S + 2HCl → 2NaCl + H2S(g)

What's The Type Of Bonding Of Sodium Sulfide? 

Sodium sulfide compound is an ionic compound. There are 2 Na atoms per 1 Sulfide atom. It has a central Sulfur atom encircled by 4 Oxygens in covalent bonds.  The Sodium atoms and Sulfur or Oxygen atoms in the compound exchange their electrons. Moreover, Sulfur is in group 6, and it requires two more electrons to attain a noble gas state of Argon.

Likewise, the remaining 2 Sodium atoms want to lose 1 electron each to become the noble gas state of Neon. Thus, the 2 Sodium atoms each provide one electron to the Sulfur atom, helping it to be stable in its outer shell.

Since the Sodium atoms give away all its extra electrons to its outermost shell, the two atoms attain the noble gas configuration of Neon and hence become stable.

FAQ (Frequently Asked Questions)

1. Is Sodium Sulfide Soluble In Water?

Sodium is a group one element, and as all the group one elements is soluble, even sodium sulfide is soluble in water. Sodium sulfide is slightly soluble in alcohol but insoluble in ethers, although the solubility of sodium sulfide depends on the temperature as it is highly soluble. Another main reason behind the solubility of sodium sulfide in water is, it is an ionic compound which tends to disassociate its ions in water.

In 0°C, approximately 12.4g/100 mL is soluble in water. Whereas in 20°C just 18.6g/100mL sodium sulphide is soluble in water.

Moreover, for hydrolysis, 50°C is required to make 39g/100mL sodium sulfide soluble.

2. How Is Industrial Sodium Sulfide Different By Laboratory Sodium Sulfide?

The industrial sodium sulfide is mostly a mixture with different numbers of crystalline water. Hence the molecular formula of sodium sulphide is Na2S • nH2O. This sodium sulfide exhibits as yellow or in reddish-brown colour, and it is flaky and granular. It is mainly used in paper, dyes, ore floatation, mineral processing, dyeing industries and printing.

The industrial sodium sulfide is classified into three categories by GB/T 10500-2000 standard. Type 1 is regular sodium sulfide which is most commonly known as a red base; The Class 2 sodium sulfide is low-iron widely known as the yellow base, and Class 3 is sodium sulfide of high content, which are usually used in industries.