What is Silica Gel?

by Lucy Bell-Young

Silica gel is a commercial desiccant – it removes moisture from the air and reduces humidity. 

When you’ve bought a new pair of shoes, you’ve probably noticed the small packets of beads that come inside the packaging. These are packets of silica gel granules. They are often included in product packaging, like electronic gadgets, telescopes, and microscopes, so as to remove moisture in the air and reduce humidity.

What Does Silica Gel Do?

  1. Commercial Desiccant

Silica gel is mainly used in industries as a desiccant, which is a substance that’s used as a drying agent. It’s is a perfect desiccant because it’s hygroscopic, i.e. highly absorbent of moisture that may form as the result of temperature changes and humidity. As a desiccant, it prevents the growth of moulds and bacteria that can ruin perishable products and electronic components. This is why it’s often used in packaging.Packets of silica gel on table

Condensation inside the packaging of products can damage the items inside. Some products, such as optical devices like telescopes, are very sensitive to moisture. The lenses and the prisms can easily become clouded and mould may form inside the device.

For the same reason, pharmaceutical products, like food supplements, have longer shelf lives because of this compound. It’s also used to help repair water-damaged electronic equipment. For instance, if your mobile phone is accidentally dropped in water, you can remove the moisture from the circuits by immersing the circuits in a bath of silica gel. 

It’s also used by communication engineers to maintain a low relative humidity inside high frequency radio transmitters and satellite transmission systems, where it helps keep the systems working as efficiently as possible.

For example, if excess moisture is present within the waveguide, it can lead to electrical arcing within the waveguide itself as the moisture acts as a conductor. This would damage the power amplifier. Water condensation inside the waveguide simultaneously affects the impedance and frequency characteristics of the system, which inevitably degrades the signal. To prevent this, a compressed air system is commonly used to circulate air within the waveguide over a jar of silica gel, effectively removing the moisture in the air.

Another application of this compound as a desiccant is drying air in industrial compressed air systems. Here, the compressed air is dried by forcing it to flow through the bed of beads. Condensation is prevented from forming and damaging the industrial systems.

A similar method is used to prevent the failure of brake air pipes on railway locomotives, where condensation can result in a weak grip of the brake system, leading to possible accidents.

  1. Chemistry Applications

Chromatography analysis would be very difficult to do without silica gel, where it’s used as a stationary phase in column chromatography. The compound’s particles used for this phase are very small because the smaller the particle size, the larger the overall surface area. Various particle sizes are used for different types of column chromatography.

Particle sizes of silica gel determine whether it’s used for either flash chromatography or gravity chromatography. As a polar compound, it means that non-polar components tend to elute before the more polar components. On the other hand, when hydrophobic groups, such as C18 groups, are attached to the gel, the polar compounds elute first. This method is called reverse phase chromatography. 

Another use of silica gel in chemistry applications is in synthesising organic compounds, as well as purifying insoluble reagents and chemical scavengers. This is made possible by converting the hydroxyl groups on the surface of silica into functionalized groups. 

Silica gel can also covalently bond with chelating groups, which can then be used to selectively remove metal ions from aqueous solutions. For greater mechanical integrity, chelating groups can be covalently bound to polyamines that have been grafted onto the surface of this compound.

Smartphone under a pile of silica gel on table
As a desiccant, silica gel can be used to remove the moisture from your phone if it’s been dropped in water

What Can You Do with Silica Gel?

Aside from the industrial and chemistry applications of silica gel, you can also use this compound in many DIY household hacks and practical applications. Here are some of them:

  • Cat litter deodorant: You can use it to deodorise a cat litter box by sprinkling some of it inside. It then works to dehydrate feces and stop bacteria growth – it’s also non toxic for kitties! 
  • Water filtration: You can even add this compound to your household filtration system, where it can adsorb heavy metals and minerals dissolved in the tap water.
  • Protection for photos: Now that digital photos can easily be uploaded online, old printed photos are more precious than ever. Moisture is the number one enemy of old printed pictures. Moisture can dissolve the chemicals on the photos and can also lead to the growth of fungi and bacteria. Luckily, storing them with sachets of silica gel can prevent this.
  • Preserve collectibles: If you have paper-based collectibles like comics and football cards, you can keep them in pristine condition by sealing them in a glass box container with silica gel – this is also a nice way to showcase them!
  • Protect important documents: Many of your important documents, such as insurance policies, deeds, wills, and legal contracts, are usually stored and barely accessed most of the time. This makes these documents more vulnerable to moisture. Adding silica gel will prevent the deterioration of your documents.
  • Remove musty smell on books: If you’ve noticed your books are developing a bit of a musty smell, put some silica gel on your bookshelf to remove it.
  • Deodorise laundry: Remove the bad smell from your laundry by placing large packets of silica gel under your laundry basket.
  • Prevent rusting: If you keep a medal or trophy box, or anything else containing metal, you can put some silica gel inside to prevent the items from rusting.

What is the Chemical Formula for Silica Gel?

Silica gel is an oxide compound of silicon with the formula SiO2. It’s an amorphous and porous form of silicon dioxide that has an irregular tridimensional framework of alternating patterns of silicon and oxygen atoms.

The molecular structure of this compound makes it highly absorbent of water. Unlike carbon atoms, however, silicon doesn’t readily form double bonds with other elements.

Chemical structure of silica gel

What Are the Chemical Properties of Silica Gel?

Silica gel is classified as an oxide of silica, which is made up of linear triatomic molecules. Each atom of silicon is covalently bonded with two oxygen atoms. Silicon dioxide exists naturally in various forms:

  • Quartz
  • Tridymite
  • Cristobalite

What is the Chemical Structure of Silica Gel?

While the various forms of silica are chemically identical to each other, their molecular structures are different. Therefore, silica compounds are classified into two groups: 

  • Amorphous: The molecular structures of these compounds are more random in pattern
  • Crystalline: These compounds have repeating patterns of silicon and oxygen


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