Ethan Clarke
Iodine is a dark purple-black solid at room temperature and is purple in a hydrocarbon solvent. It is a nonpolar substance with small molecules. Plastic, on the other hand, is a polymeric material with a complex 3D structure built of millions of small and identical molecules connected to each other. Due to the presence of micropores and molecular voids in plastic, iodine molecules can infiltrate and occupy the hollow spaces inside the plastic through a process called diffusion. This is why plastic bags are permeable to iodine and it is not recommended to store iodine in a plastic bag.
| Characteristics | Values |
|---|---|
| Iodine molecules | Can infiltrate through micropores inside plastic |
| Iodine molecules | Occupy the free space inside the plastic |
| Iodine molecules | Can remain inside plastic for a long time |
| Plastic | Consists of almost nonpolar molecules |
| Iodine molecules | Are nonpolar |
| Iodine diffusion inside plastic | Is a slow process |
| Iodine | Is permeable to plastics |
| Plastic | Is a selectively permeable membrane |
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What You'll Learn
Iodine can permeate plastic bags
In the experiment, students place a teaspoon of corn starch and half a cup of water in a plastic bag. They then fill a beaker with water and add iodine, before placing the bag in the beaker so that the corn starch mixture is submerged in the iodine water. The iodine will then cross into the bag and turn the starch purple. The plastic bag is permeable to iodine, but not to starch.
This experiment demonstrates the concept of a semi-permeable membrane, which only allows certain substances to pass through. In this case, the plastic bag acts as a semi-permeable membrane, allowing iodine to pass through but not starch or water. This is because plastic consists of polymers with complex three-dimensional structures built from millions of small, identical molecules called monomers. There is always some free space or hollows inside the 3D structure of these molecules, which small iodine molecules can occupy.
The diffusion of iodine inside plastic is a slow process, as it takes time for iodine to fill in the molecular voids in plastic. Iodine molecules can remain inside the plastic for a long time. This is why iodine can stain plastic, as the molecules get stuck in the coils of the plastic's molecular structure.
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Iodine molecules are small enough to infiltrate plastic
Plastic is a polymeric material, such as polyethylene or polypropylene. Polymers have a complex three-dimensional (3D) structure built of a large number of small and usually identical molecules connected to each other. These molecules are called monomers, and polymers are also called macromolecules. There is always some free space or hollows inside the 3D structure of such molecules. Iodine molecules are small enough to infiltrate plastic and may occupy these hollows.
Diffusion is a process of spreading the molecules of one substance among the molecules of another substance. In other words, molecules of two substances mix together. Usually, this process is mutual. Through diffusion, molecules occupy all the available space around. Ultimately, the concentration of particles (number of molecules per volume unit) becomes even in every part of the system. Iodine diffusion inside plastic proceeds rather slowly. It takes a while for iodine to fill in molecular voids in plastic.
In a lab experiment, iodine is often used to demonstrate the concept of a semi-permeable membrane. Students fill a plastic bag with corn starch and water, seal the bag, and then submerge it in a solution of iodine. The iodine will cross into the bag and turn the starch purple. This demonstrates that the iodine molecules are small enough to infiltrate the plastic bag and that the plastic bag is permeable to iodine.
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Iodine molecules occupy the free space inside plastic
Plastic is a polymeric material, such as polyethylene or polypropylene. Polymers are large molecules with complex three-dimensional (3D) structures composed of a vast number of smaller, identical molecules called monomers. The 3D structure of polymers contains free space or hollows.
Iodine is a small molecule that can infiltrate plastic through its micropores. Iodine molecules may occupy the free space inside the plastic material, where they can stay for long periods. This process is known as diffusion, where molecules spread and mix to occupy all available space, resulting in an even concentration throughout the system.
Diffusion of iodine inside plastic occurs slowly, and it takes time for iodine to fill the molecular voids. Iodine molecules can remain inside the plastic even when a reducing agent is applied, as the plastic acts as a barrier, preventing the reducing agent from reaching the iodine molecules.
In laboratory experiments, iodine is often used to demonstrate diffusion through semi-permeable membranes. Iodine is an indicator for starch, meaning it changes colour in the presence of starch. When a plastic bag containing starch is submerged in an iodine solution, the iodine permeates the bag, turning the starch purple, while the iodine solution outside retains its original colour. This experiment illustrates the selective permeability of plastic, allowing certain substances to pass through while blocking others.
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Iodine molecules react with substances inside plastic
Plastic is a polymeric material, such as polyethylene or polypropylene. Polymers are large molecules with complex three-dimensional structures, built from a huge number of smaller, identical molecules called monomers. There is always some free space or hollows inside the 3D structure of polymer molecules.
Iodine (I2) is a small, nonpolar molecule. Due to its small size, iodine can infiltrate plastic through its micropores and occupy the hollow spaces inside the polymer molecules. This process is known as diffusion, where molecules spread and mix to fill all available space. Iodine diffusion inside plastic occurs slowly, taking time to fill in the molecular voids.
Iodine's nonpolar nature also plays a role in its interaction with plastic. In chemistry, substances of similar nature tend to mix or dissolve in each other. As plastic consists of mostly nonpolar molecules, iodine "'feels comfortable" moving into and staying inside plastic.
In experiments, iodine is often used to demonstrate diffusion and semi-permeable membranes. When iodine is placed outside a plastic bag containing starch and water, it diffuses into the bag, turning the starch purple. This occurs because the plastic bag acts as a semi-permeable membrane, allowing small molecules like iodine to pass through while blocking larger molecules like starch.
Overall, iodine molecules can react with substances inside plastic due to their small size, nonpolar nature, and ability to diffuse through the micropores and hollow spaces within plastic's polymeric structure.
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Iodine diffusion inside plastic is slow
Plastic is a polymeric material, such as polyethylene or polypropylene, with a complex three-dimensional structure. It is made up of a large number of small, usually identical molecules called monomers. These molecules have a lot of free space or hollows inside them. Iodine molecules, being small, can infiltrate through the micropores in plastic and occupy these hollows.
Diffusion is the process of spreading the molecules of one substance among the molecules of another substance. Iodine diffusion inside plastic is slow because it takes time for iodine to fill in the molecular voids in plastic. If enough time is not given, the plastic will only be slightly coloured.
Iodine is a dark purple-black solid at room temperature and is purple in a hydrocarbon solvent. It is a known indicator for starch, meaning it changes colour in the presence of starch. When starch is mixed with iodine in water, an intensely blue or purple-black coloured starch/iodine complex is formed.
In a lab experiment, students can observe iodine diffusion through a plastic bag. Corn starch and water are mixed in a plastic bag, which is then submerged into a solution of iodine. The iodine will cross into the bag and turn the starch purple. This experiment demonstrates that plastic is semi-permeable, meaning it has microscopic openings that allow small amounts of substances like iodine to pass through.
Iodine should not be stored in a plastic bag because it can permeate the bag and leak out.
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Frequently asked questions
Iodine can permeate plastic and infiltrate through its micropores.
Iodine molecules are small and nonpolar, and plastic consists of almost nonpolar molecules, so iodine can move into plastic through its micropores.
In a simple lab experiment, iodine can be used to demonstrate diffusion across a semi-permeable membrane. Corn starch is placed in a plastic bag and submerged into a solution of iodine. The iodine will cross into the bag and turn the starch purple.
Iodine can permeate plastic, so storing iodine in a plastic bag may result in some outflow of iodine.
