Gravity Filtration vs Vacuum Filtration

What Is Filtration?

Filtration is a process through which you can separate a substance into different substances. The solid particles in liquid or gaseous fluid can be removed by a use of filter medium that permits the filtrate to pass the fluid but the solid particles retain on the filter medium.

Why Do We Need Filtration?

Before knowing the need and importance of filtration, it’s necessary to know about two main and crucial purposes of filtration due to which it becomes significant in our daily life.

• In order to entrap solid material suspended in any fluid filtration is used.
• Filtration is used to produce liquid matter where the solid has been suspended.

So we need filtration in so many daily life purposes including water distillation as well as purification, municipal waste treatment and so many other things involving the process of filtration which provide strength to its importance.

Types of Filtration in Organic Chemistry

There are two types of filtration that are commonly used in organic chemistry laboratories.

• Gravity filtration – also known as simple filtration
• Vacuum filtration – also known as suction filtration

Now the Question Arises!!

What is the difference between gravity filtration and vacuum filtration?

When to use gravity vs vacuum filtration?

And what equipment do you need for each type of filtration?

1. Gravity Filtration – Simple Filtration

This is the most common method of filtration and is used to remove any insoluble (solid) impurities from an organic liquid under gravity.

The solid impurity could be the required product, any additive impurity such as drying agent, leftover reactant or any inadmissible side item.

Apparatus to Perform Gravity Filtration

The apparatus needed for the performance of gravity filtration includes;

• Filter paper – to separate solid particles from fluid
• Filter funnel
• Retort stand set – to hold the funnel
• Conical flask – to collect the filtrate

Procedure

Now, let’s have a look at the complete procedure and steps for the performance of standard gravity filtration in an organic chemistry laboratory.

Choose Size of Filter Paper

First, we need to choose the right size of the filter paper according to the diameter of the funnel that when folded should be a few millimeters below the rim of your filter paper.

For standard size filter funnels where walls are of 58 and 60 degree you can find the right size of filter paper in the given table below.

So you can choose the right size of filter paper with respect to the diameter of the funnel by using this given table easily.

Folding of Filter Paper

After choosing a filter paper, now fold it into the cone shape. First folding it into half and then again in half.

Fit the Funnel in Stand

Now use a retort stand set to fit the funnel in a ring or place it in the neck of the Erlenmeyer flask. It holds the funnel while filtration letting hands free.

Set the Paper Inside Funnel

Fit the filter paper inside the funnel. But first use a few drops of solvent that is going to be used in the procedure to wet the filter paper. Wetting the filter paper holds it in place perfectly against the glass funnel.

Pour the Mixture

Finally and last, now pour the mixture required to be filtered through the glass funnel. Pour it in portions if necessary. The solid impurities will be on the top of filter paper while the filtrate collected in the funnel.

Pro Tip!!

A fluted filter paper is often better to be used with organic solvents for gravity filtration. This folding will provide more surface area on which to collect solid impurity and pass liquid quickly through filter paper.

A diagram for the folding of fluted filter paper and cone is given below.

2. Vacuum Filtration – Suction Filtration

Vacuum filtration is basically a fast and efficient way of filtration. In vacuum filtration, desired solids are separated from the liquids. For instance, the collection of crystals in the recrystallization process done by vacuum filtration.

A partial vacuum is created, on one side of the funnel,  to increase the rate of filtration and also for drying of solid.

Apparatus to Perform Vacuum Filtration

In order to perform vacuum filtration which is also known as buchner filtration following apparatus is needed;

• Buchner funnel
• Vacuum filtration flask – also buchner flask
• Filter paper – to separate desired solid from liquid
• Adjoining cones
• Retort stand set – to hold the flask firmly
• Tubing – to join the flask with vacuum pump
• Vacuum pump – to create vacuum either electrical or water stream vacuum pump

Procedure

Now let me describe to you the whole procedure of vacuum filtration in the following steps to create a sense of differentiation between two filtration methods of organic chemistry.

Selecting Right Filter Paper

Choosing the right material and size of filter paper will surely give you the desired results. You can use cellulose filter papers, membranes and also glass microfiber for vacuum filtration.

Set-up the Apparatus

Take the vacuum filtration flask and clamp it securely with the ring of retort stand set. Also add the buchner funnel with use of adjoining cones because they are adjustable to fit in any flask to the funnel in place of rubber bung.

Place Filter Paper in Funnel

Now place a filter paper in a funnel that is of the right material and pores size. It should be of small size to remain flat, but large enough to cover all the holes in the filter. You can also cut a larger filter paper into a small size to fit in the funnel.

Connect Vacuum Filtration Flask With Vacuum Pump

Connect the vacuum filtration flask with a vacuum pump which can either be electrical or a water stream vacuum pump.

Always use thick-walled tubings to join the flask with vacuum pump since tygon tubing will collapse under reduced pressure.

Wetting the Filter Paper

Wet the filter paper with a small amount of solvent to be used in the procedure of filtration. This will cause the filter paper to adhere to the plate firmly and keep the material from passing under the paper while filtration.

Pour the Mixture

Now pour the mixture to be filtered onto the filter paper. The vacuum will rapidly pull the liquid through the funnel – efficient filtration.

If particulates creep over the edges of paper, then carefully pour the portions of mixture again onto the very center of paper.

Collect Desired Solid

In order to collect, the desired solid carefully disconnects the rubber tubings. Remove the filter paper and collect the solid that is leftover onto it.

Usually you need to air dry the solid after collecting onto the watch glass for a while.

When to Use Gravity Filtration vs Vacuum Filtration?

Both gravity filtration and vacuum filtration is a technique used to get the desired product. But in contrast we need to use gravity filtration to isolate the filtrate (the liquid) and we need to use vacuum filtration to isolate the precipitate (the solid).

Bottom line!!

Hope you get some beneficial information from our article and learn the difference between two different filtration methods of organic chemistry that are commonly used in laboratories.

Frequently Asked Questions (FAQ’s)

Why Is Gravity Filtration Used Instead of Vacuum Filtration?

Gravity filtration involves no complexity of apparatus and is an easy way of collecting precipitates or solid impurities from an  organic liquid instead of vacuum filtration.

Does Filtration Work Against Gravity?

No, filtration doesn’t work against gravity; instead gravity filtration and gravity water filters use the force of gravity to pull the filtrate (liquid) down while it filters.

Is Gravity Filtration the Same as Vacuum Filtration?

No, they are not the same. Gravity filtration is used to remove solid impurities from desired liquid while on the other hand vacuum filtration is used to collect the desired solid. Also vacuum filtration is usually much faster than gravity filtration.