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

1. 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) 

2. As a catalyst - Tin(II) Chloride is used as a catalyst in the production of plastic polylactic acid (PLA).

3. 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.

4. 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.

5. 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:

1. 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.

2. Dilute the mixture with water and mix the resulting solution.

3. Once the solvent has completely dissolved, transfer 50 ml of the resulting solution into a 500 ml conical flask. 

4. Add potassium sodium tartrate in the amount of 5 g into the conical flask.

5. 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. 

6. 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.

7. 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”.