Separation funnel: which one to choose and at what price

November 2, 2021

When separating a heterogeneous mixture with different densities, an instrument known as a separatory funnel must be used . Also known as a separatory funnel, it is a glass utensil that is on the shelves and cannot be missing in chemistry laboratories. But which one to choose?

What is decantation?

When separating mixtures there are several types of known procedures, such as ‘gravitation’, which is separation by suspension. However, there is another process used exclusively for heterogeneous liquid mixtures known as decantation.

It is a technique for separating heterogeneous mixtures between an insoluble liquid or two liquids that cannot be mixed homogeneously. For example, water and oil. Where the water is denser than the oil so they are located in different layers.

There is also the solid-liquid decantation, which is a type of separation to divide the solid particles of a mixture that accumulates in the liquid and must be extracted through a chemical or physical method.

What is the separatory funnel?

Having learned what decantation is, it is time to talk about the laboratory utensil. The separating funnel is a glass and pear-shaped instrument that allows the separation of the mixtures to be carried out by draining the solutions.

The separatory funnel has a stopcock at the bottom and a plug at the top. The instruments follow the process of immiscible liquids, which is the natural separation of solutions according to the layers that are formed by the density of the liquids.

Separation funnel parts

The separating funnel has several areas that are worth knowing to understand how it works. Let’s see what they are and how they work.

Plug

The stopper sits at the top of the separatory funnel, and like the body, it is made of glass. Although some manufacturers prefer Teflon because of its strength. The purpose of the stopper is to stop the flow of the mixtures so that they do not leak out of the funnel. It is also the duct through which the less dense liquid is deposited into a receiving flask.

Pear body

The body of the funnel is pear-shaped and is where the mixtures rest while the natural separation process occurs. It is made of glass and is extremely delicate to the touch. So it should be kept in a shock-free area, such as a bookshelf, and handled with care.

Stopcock

The stopcock is located at the bottom of the separatory funnel and has two functions: to seal and to allow the mixture to pass. It houses a thread that opens via a conduit-type wrench and must be handled carefully to avoid damaging the glass structure of the funnel.

How to choose a separatory funnel?

If you are interested in buying a separatory funnel for your laboratory, there are a couple of things to keep in mind that help guide your choice. This so that you do not think about the store and choose a bad product.

By the materials of the funnel

First of all, you should review the material of the instrument to avoid replicas and scams in the elaboration of the funnel. Since there are models of separating funnels made of plastic. This is scientifically unacceptable and is detrimental to its use in the laboratory. The utensil should always be glass and pear-shaped.

By the size of the funnel

On the other hand, knowing the size of the funnel is extremely important when choosing a settling unit. These should be a standard size of 30 milliliters and 3 liters . Although depending on the type of laboratory and the amount of mixtures to handle, you will need a larger unit. In fact, those are the ones used in centrifuges.

How do you use a separatory funnel?

The funnel follows a handling process established by protocols. To illustrate the procedure, we will use as an example liquid-liquid decantation with water and oil solutions. According to the theory, the instrument will force the separation of liquids naturally through two layers.

The first step is to take a large test tube to deposit a certain amount of water. Then open the funnel cap and deposit it. Then another test tube is used to deposit a similar amount of oil and the same procedure is carried out by depositing it on the pear-shaped utensil.

Since they are immiscible liquids, the solvents will not unify, but will separate by phases or layers. This separation procedure has to be carried out by shaking the instrument. The tap is opened momentarily to let the gases escape and then it is shaken . This process should be carried out approximately 4-5 times until it is free of gases.

The funnel is then placed on a universal support so that, in a stationary and natural way, the solvent layers separate. Positioning the densest liquid at the bottom, while the least dense at the top. It is not something that happens immediately so you have to wait for the separation of the solute mixture.

Finally, when separated, they must be deposited in the containers. The stopcock is first opened over a flask for the dense solute and sealed when visualizing the less dense liquid. While the latter is deposited into another container through the upper plug.

Separation funnel safety

When handling the separation funnel, a security protocol must be followed. Since they are delicate utensils, stirring and gripping pressure must be done carefully, avoiding rough handling in experiments.

The same happens when cleaning. Be careful with excessive pressure. Especially when they are shaken to remove particles and liquid residue. Finally, avoid accumulation of mixtures by routinely opening the top cap with the funnel pointing outward.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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