Why does Reverse Osmosis work?

Reverse Osmosis is widely known for its usefulness and what is the reason why it works so well? Well, it basically helps to remove impurities from a solution.

Looking at a atomic level or a molecular level, it is very evident that it is a great idea.

• Firstly, we must understand and acknowledge that the water molecules are far smaller than the other kinds of molecules such as ion, etc.
• Secondly, we must also understand the meaning of semi-permeable membrane:
• A membrane is a thin piece of sheet that does not allow molecules to pass, be it small or big.
• Semi means half so semi-permeable membrane means a thin sheet of material that only allows small molecules to pass. 
• As there is a presence of holes in the membrane, it thus allows smaller molecules to pass through.
• However, in Reverse Osmosis, it usually only allows water molecules to pass as other molecules are too big for to pass through these holes.
• Thus, the key reason to why Reverse Osmosis is excellent!

So how does Reverse Osmosis exactly work? Let's observe it through an experiment.

1. Seawater is pumped into the set-up and force is applied to the seawater. 
2. Seawater is constantly supplied.
3. When the seawater contacts the membrane, salt molecules will be trapped and cannot pass through it.
4. However, water molecules are able to pass through it.
5. Therefore, the result of Reverse Osmosis will be pure water.

Why does this experiment work in this way?

• This is mainly because
• The salt molecules are bigger than the holes in the semi-permeable membrane. 
• However, the water molecules are smaller and thus are able to smoothly pass through it as the semi-permeable membrane allows so.
• Thus, one side will have the seawater while the other will have pure water. 

So, Reverse Osmosis is basically the usage of the semi-permeable membrane as a filter and making the solvent purer by means of forcing it through the semi-permeable membrane.

If you feel lost, refer to this picture, it may be better:

However, you may understand Reverse Osmosis better through this video: http://www.youtube.com/watch?v=rG29fwWoNkc&feature=related