Key Properties and Real-World Uses of Stannous Chloride
The chemical name of Stannous Chloride is Tin(II) Chloride. The chemical formula of stannous chloride is SnCl2. Stannous Chloride in its solid state is observed as a crystalline mass. Its dyes form a stable dihydrate; however, upon reacting with aqueous solutions, they tend to undergo hydrolysis, especially if the compound is hot.
Tin(II) Chloride is alternatively also referred to as Dichlorotin, Tin dichloride, Stannous Chloride or even Tin Protochloride. One of the noticeable features of the compound is the lone pair of electrons in the molecule which during the gaseous state is bent. Tin(II) Chloride as a compound does not possess any distinctive odour. However, the compound is highly toxic and has been reported to cause irritation to the eyes and skin when brought into contact. There are a variety of industrial uses for the compound as we shall later study. Given below are the various Tin(II) Chloride structures:
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Properties of Stannous Chloride
The molecular weight of anhydrous Tin(II) Chloride: 189.60 g/mol
The molecular weight of dihydrate Tin(II) Chloride: 225.63 g/mol
The appearance of Tin(II) Chloride: White crystalline solid
The density of anhydrous Tin(II) Chloride: 3.95 g/cm3
The density of dihydrate Tin(II) Chloride: 2.71 g/cm3
The melting point of anhydrous Tin(II) Chloride: 247 °C
The melting point of dihydrate Tin(II) Chloride: 623 °C
The boiling point of Tin(II) Chloride: 623 °C
Solubility in water: 83.9 g/100 ml
Stannous Chloride Structure
The crystal structure of stannous chloride is a layered structure. In terms of coordination geometry, the shape could be expressed as being a trigonal pyramid in the anhydrous state. In a dihydrate state, there is also a three-coordinate structure.
Stannous Chloride Uses
As a strong reducing agent - The most common application for such a use would involve silvering of mirrors, where the precious metal is deposited on the glass to give way to the reflective surface. The equation is as follows: Sn2+ (aq) + 2Ag+ ➝ Sn4+ (aq) + 2Ag (s)
As a catalyst - Tin(II) Chloride is used as a catalyst in the production of plastic polylactic acid (PLA).
As a mordant in dyeing - Tin(II) Chloride is commonly used as a mordant. A mordant refers to a substance which is used along with the dye to allow the colour to attach itself to the fabric. In this case, Tin(II) Chloride forms a coordination complex with the dye to attach the dye to the fabric.
As a food additive - Food additives are used in food to enhance the flavour, taste or otherwise overall presentation. Tin(II) Chloride is used in a number of canned and bottled foods where the compound is used for its anti-oxidation properties and for its ability as a colour retention agent.
Laboratory use as a reducing agent - One of the most paramount uses of the compound has been in organic chemistry, where the compound is used in the Stephen reduction. In Stephen reduction, a nitrile is reduced using an imidoyl chloride salt to an imine which can then be hydrolysed subsequently to form an aldehyde. The compound is also used in the Sonn-Muller method.
Method of Assay - Tin(II) Chloride
Assaying is a chemical process undertaken on a metal or an ore to evaluate the composite ingredients and the overall quality. Here is the method of the assay:
Take 2 g of Tin(II) Chloride and dissolve it in a 250 ml flask consisting of 25 ml hydrochloric acid. Make sure that the compound added is weighed exactly and there is no room for any error margin.
Dilute the mixture with water and mix the resulting solution.
Once the solvent has completely dissolved, transfer 50 ml of the resulting solution into a 500 ml conical flask.
Add potassium sodium tartrate in the amount of 5 g into the conical flask.
To the resulting solution, add a cold saturated solution of NaHCO3. Keep adding the cold saturated solution until the resultant solution in the conical flask becomes alkaline. Use the litmus paper test to verify the alkaline nature of the solution.
After the solution is prepared, titrate the solution with 0.1 N iodine. It is important to use starch as an indicator in this case.
For measurement sake, 1 ml for 0.1 N iodine used is equal to 11.28 mg of SnCl2.2H2O.
Note: Please note that while stannous salts are easily oxidised, the water used in the above procedure should preferably be “oxygen-free”. To achieve this result, purge the water with gases like carbon dioxide or nitrogen. Concurrently, even the iodine solution used should preferably be “oxygen-free”.
FAQs on Stannous Chloride: Structure, Uses, and Reactions
1. What is Stannous Chloride, and what is its chemical formula?
Stannous Chloride is an inorganic compound with the chemical formula SnCl₂. It is also commonly known as tin(II) chloride, indicating that the tin atom is in its +2 oxidation state. It appears as a white crystalline solid and is a key reagent in chemistry, primarily valued for its properties as a strong reducing agent and as a catalyst.
2. What are the key physical properties of Stannous Chloride (SnCl₂)?
Stannous Chloride has several distinct physical properties that are important for its application and handling:
- Appearance: It is a white crystalline solid at standard temperature and pressure.
- Solubility: It is soluble in small amounts of water and other polar solvents like ethanol and acetone. However, in large amounts of water, it undergoes hydrolysis.
- Structure: In its solid form, it has a polymeric chain structure. In the gaseous phase, it exists as a bent, monomeric molecule.
- Melting Point: It has a relatively low melting point of 247°C.
3. What are the major industrial and laboratory uses of Stannous Chloride?
Stannous Chloride is a versatile chemical with numerous applications:
- Reducing Agent: Its primary use is as a reducing agent. It is used in the Stephen's reduction to synthesise aldehydes and to reduce ferric ions (Fe³⁺) to ferrous ions (Fe²⁺).
- Mordant in Dyeing: In the textile industry, it acts as a mordant, helping to fix dyes onto fabrics like cotton and silk.
- Food Additive: It is used as an antioxidant (E number E512) and colour-retention agent in certain canned and bottled foods.
- Catalyst: It serves as a catalyst in the production of polylactic acid (PLA), a type of biodegradable plastic.
- Tin Plating: It is a key component in electrolytes for tin-plating steel to prevent corrosion.
4. Why does Stannous Chloride (SnCl₂) act as a strong reducing agent in chemical reactions?
Stannous Chloride acts as a strong reducing agent because the tin atom in SnCl₂ is in the +2 oxidation state. The +4 oxidation state (Sn⁴⁺) is significantly more stable for tin. Consequently, the Sn²⁺ ion has a strong tendency to lose two more electrons to achieve this more stable Sn⁴⁺ state. By readily giving up its electrons (undergoing oxidation), it causes the other substance in the reaction to gain electrons (undergo reduction), which defines it as an effective reducing agent.
5. How does the structure of Stannous Chloride differ between its gaseous and solid states?
The molecular structure of Stannous Chloride changes based on its physical state, which is a key concept in chemical bonding:
- In the gaseous state, SnCl₂ exists as a simple, discrete bent molecule. It has a V-shape with a Cl-Sn-Cl bond angle of about 95°, which is predicted by VSEPR theory.
- In the solid crystalline state, it does not exist as individual molecules but forms a polymeric chain structure. Each tin atom is coordinated with three chloride atoms, creating layers and giving it its crystalline properties.
6. Why does an aqueous solution of Stannous Chloride turn milky when diluted with excess water?
An aqueous solution of Stannous Chloride turns milky or turbid upon significant dilution due to a chemical process called hydrolysis. In the presence of excess water, SnCl₂ reacts to form an insoluble basic salt, tin(II) oxychloride (Sn(OH)Cl). The formation of this fine, white precipitate is what causes the cloudy appearance. The reaction is represented as: SnCl₂ + H₂O ⇌ Sn(OH)Cl(s) + HCl(aq). To prevent this, solutions of SnCl₂ are typically prepared in dilute hydrochloric acid, which shifts the equilibrium to the left, keeping the compound dissolved.
7. How can one perform a chemical test to confirm the presence of stannous ions (Sn²⁺) in a given sample?
A standard confirmatory test for stannous ions (Sn²⁺) involves using a solution of mercuric chloride (HgCl₂). The procedure is as follows:
- First, dissolve the sample in dilute hydrochloric acid.
- To this solution, add mercuric chloride solution dropwise.
- The Sn²⁺ ions will reduce the Hg²⁺ ions. Initially, a white precipitate of mercurous chloride (Hg₂Cl₂) will form.
- If more stannous ions are present, this white precipitate is further reduced to a grey or black precipitate of metallic mercury (Hg).
This distinct, two-stage colour change from a clear solution to a white, then grey/black precipitate is a definitive test for the presence of a stannous compound.
