Difference Between Sodium Fluoride and Calcium Fluoride

Key Difference – Sodium Fluoride vs Calcium Fluoride
 

Sodium Fluoride and Calcium Fluoride are two fluoride minerals of the elements in the group I and group II of the periodic table. While they naturally exist in minerals form, they are also commercially produced for industrial applications. But, natural form of sodium fluoride is comparatively rare, and calcium fluoride is very abundant. This can be considered the key difference between Sodium Fluoride and Calcium Fluoride. Although, they are both fluorides containing crystalline solids, their industrial applications vary widely; they are used for various purposes.

What is Sodium Fluoride?

Sodium fluoride is a colorless, inorganic, ionic chemical compound with the molecular formula NaF. Like sodium chloride, it dissolves in water giving Na⁺ and F^– separately.

NaF (s)           →        Na⁺ (aq)           +          F^– (aq)

Sodium fluoride naturally exists as a mineral called ‘villiaumite,’ which is relatively rare and it can be found in plutonic nepheline syenite rocks.

Sodium chloride is one of the most widely used fluoride ion sources in many industrial applications since it is less expensive and less hygroscopic compound than potassium fluoride (KF).

What is Calcium Fluoride?

Calcium fluoride is a white, water-insoluble, inorganic, ionic chemical solid compound with the molecular formula CaF₂. It is also known as fluorspar, and it naturally exists as a mineral fluorite and possesses a deep colouration due to its impurities. The fluorite mineral can be found in many places, and it is used as a precursor to HF. But, some industrial processes require pure calcium floride, with no impurities. Thus, high purity CaF₂ is industrially produced by using calcium carbonate and hydrogen fluoride.

CaCO₃     +       2 HF    →     CaF₂    +      CO₂     +      H₂O

What is the difference between Sodium Fluoride and Calcium Fluoride?

Chemical Structure of Sodium Fluoride and Calcium Fluoride

Sodium Fluoride:

Sodium fluoride is an ionic crystal which crystallizes in a cubic motif. In its structure, both Na⁺ and F⁻ contains octahedral coordination sites, and its lattice spacing is approximately equal to 462 pm. This length is fairly smaller than that of sodium chloride.

Calcium Fluoride:

Calcium fluoride naturally exists in fluorite form and it crystallizes a cubic motif. Ca²⁺ serves as eight-coordinated centers and is  located in a box for eight F^– centers. Each F^– center is coordinated to four Ca²⁺ centers. Generally, perfectly packed crystals are colorless, but the mineral possesses a deep color  due to F-centers.

The structure of a unit cell of CaF₂ (fluorite) is shown below.

Uses of Sodium Fluoride and Calcium Fluoride

Sodium Fluoride:

Sodium fluoride is extensively used in a wide range of industrial applications including medical and  chemical industry. In medical applications, it is used in medical imaging and in the treatment of osteoporosis. In chemical industry, it is used in the synthesis and extraction processes in metallurgy, as a cleaning agent and as a stomach poison for plant feeding insects.

It is also used in water treatment. It is added to drinking water in water-fluoridation to increase the fluoride level in the water. In some countries, it is added to some food products.

Calcium Fluoride:

Both, naturally occurring and commercially produced CaF₂ are equally important in many industrial applications. It is naturally present in the fluorite mineral, and it is the main source of hydrogen fluoride manufacturing process. The reaction between fluorite mineral and the concentrated sulfuric acid produces hydrogen fluoride.

CaF₂     +   Conc H₂SO₄      →    CaSO₄ (solid)    +    2 HF

In addition, it is used to produce optical components due to its special properties. It is transparent over a broad range of frequencies; from ultraviolet (UV) to infrared (IR), low refractive index and the insolubility in water. It is used to manufacture windows and lenses used in thermal imaging systems, spectroscopy, and excimer lasers.

 

Image Courtesy:

“Villiamumite in nepheline syenite Sodium fluoride…” by Dave Dyet – shutterstone.com, dyet.com – Own work (Public Domain) via Commons Wikimedia 

“Calcium Floride” (Public Domain) via Commons Wikimedia

“Sodium Floride” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia

“Crystal structure of fluorite” by Materialscientist at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia