How does vacuum filtration work

A filter is used to separate out the solid from the liquid solution and the vacuum pump forces the liquid through the filter. It is used mostly used when particles dissolved in a solvent and then recovered through heating, so the liquid evaporates.

When vacuum filtration is used to collect solids that have been recrystallized, the contents left after the evaporation process are deposited from the flask or beaker onto a filter paper and put into a Buchner funnel.

A filter flask is attached to the funnel and the air is sucked out of the side opening through a rubber tube that is attached to the vacuum. The sample is poured into the funnel or filter paper, and the vacuum forces the solvent through the paper and it gets deposited in the filter flask. Testing the suction is critical to the process.

The rubber tube gets attached to the vacuum first and tested for suction at the other end of the tube. When the connection is secure, the filter flask should have the suction needed for the procedure.

The vacuum filtration system will remove as much of the solids from the solvent as possible and the solids remaining will be collected and weighed. Saturated solutions cannot dissolve any additional solids and are generally clear. Supersaturated solutions have sinking or suspended particles and are usually not clear.

Unsaturated solutions can work to dissolve more solids. Mostly, it is clear with no suspended particles. The solutions with suspended particles can be separated using vacuum filtration. However, unsaturated solutions usually require heating or a chemical treatment before the vacuum filtration process can be successful. Saturated solutions generally cannot be separated using vacuum filtration, but there are some cases where few particles may be collected when the pore size of the filter paper is adequate.

The amount of the solid that is collected using vacuum filtration depends on the size of the pores in the filter paper. The amount of the solid material increases through this method, as the size of the pores in the filter paper decreases. Larger pore sizes yield less solid materials, because more of the material will be pulled through the filter. Vacuum Filtration Vacuum filtration is a laboratory procedure that utilizes an oil-free vacuum pump, filter apparatus, filter flask, and often a filtration manifold to perform membrane filtration protocols.

Home Lab Filtration Vacuum Filtration 4 product s found. Show Details. How does it work? How do you test the suction of a vacuum filtration system? How much of the solids are removed using this method? What is the difference between saturated, supersaturated, and unsaturated solutions? To demonstrate the importance of a rinse, Figure 1. The yellow liquid seemed to be somewhat retained by the solid, as the first crystals collected had a yellow tint Figure 1.

However, rinsing with a few portions of cold solvent were effective at removing the yellow liquid Figure 1. A vacuum source is necessary for suction filtration and vacuum distillation. Although many science buildings come equipped with a house vacuum system Figure 1. Therefore, it is recommended to instead connect a suction flask to a water aspirator.

A water aspirator is an inexpensive attachment to a water spigot, and the nub on the aspirator connects with tubing to the vessel to be evacuated Figure 1. As water flows through the faucet and the aspirator, suction is created in the flask. A water aspirator creates suction through the Bernoulli Principle technically, the Venturi Effect , for liquids. Water coming from the faucet is constricted inside the aspirator Figure 1. As the water flow must be the same going into the aspirator as it is going out, the water speed must increase in the constricted area in the direction of flow.

A similar phenomenon can be seen in creeks and rivers where the water flows the fastest at the narrowest portions of streams. When the water increases its velocity in the direction of the water flow, conservation of energy dictates that its velocity in perpendicular directions must decrease.

The result is a lowered pressure adjacent to the fast-moving liquid. In other words, the gain in velocity of the constricted liquid is balanced by a reduction in pressure on the surrounding material the gas. For this reason, the speed at which the water flows through the faucet is correlated with the amount of suction experienced in the connected flask. A strong flow of water will have the fastest speeds through the aspirator and the greatest reduction in pressure.

Connect thick-walled hosing from the side arm to a vacuum trap and the water aspirator. Place a vacuum sleeve on the Buchner or Hirsch funnel, then filter paper on the funnel so it arches downward. The solvent should drain with suction.

Swirl the mixture to be filtered to dislodge the solid from the sides of the flask. Apply suction again for a few minutes repeat the rinse step if necessary. Dry the solid on a watch glass along with the filter paper, overnight if possible. The solid will flake off the paper when dried. Table 1. Lisa Nichols Butte Community College.

Complete text is available online. Suction Filtration Overview Suction filtration vacuum filtration is the standard technique used for separating a solid-liquid mixture when the goal is to retain the solid for example in crystallization.

Figure 1. Rinsing As the goal of suction filtration is to fully separate a solid from its surrounding liquid, rinsing the solid is necessary if the liquid cannot easily evaporate.

Water Aspirator A vacuum source is necessary for suction filtration and vacuum distillation. Step-by-Step Procedures Figure 1. The arrows show the direction of suction. Assemble the suction filtration flask Clamp a side-arm Erlenmeyer flask to a ring stand or latticework and attach a thick-walled rubber hose to its side arm.

Connect this thick tubing to a " vacuum trap " Figure 1. It is best to not bend or strain the tubing as much as is practical, as this may cause poor suction. A vacuum trap is necessary when connecting apparatuses to a vacuum source as changes in pressure can cause back-suction. When using a water aspirator, back-suction might cause water from the sink to be pulled into the vacuum line and flask ruining the filtrate , or the filtrate to be pulled into the water stream contaminating the water supply.

Place a rubber sleeve or filter adapter and Buchner funnel atop the side-arm Erlenmeyer flask Figure 1. Alternatively use a Hirsch funnel for small scales Figure 1. Obtain a filter paper that will fit perfectly into the Buchner or Hirsch funnel.

Filter papers are not completely flat and have a subtle arc to their shape Figure 1. Place the filter paper inside the funnel concave side down Figure 1.

The paper should cover all the holes in the funnel, and with the paper arching downward Figure 1. Turn on the faucet connected to the water aspirator to create a strong flow of water the degree of suction is related to the water flow. Wet the filter paper with cold solvent using the same solvent used in crystallization, if applicable, Figure 1.