Why vacuum filtration

Vacuum filtration is used to collect a desired solid too. But compare with gravity filtration, it is much faster in the result of the solvent and air being forced through the filter paper by the application of reduced pressure. Remember, never use vacuum filtration to filter a solid from a liquid if you want to use the liquid, and the solvent boiling at about degrees or lower will boil off in the vacuum flask while the pressure is reduced.

Similar to gravity filtration, a solid-liquid mixture is poured onto a filter paper, with the main difference being that the process is aided by suction beneath the funnel Figures 1. The process has advantages and disadvantages in comparison to gravity filtration.

Advantages: 1 Suction filtration is much faster than gravity filtration, often taking less than one minute with good seals and a good vacuum source. This is especially important in crystallization, as the liquid may contain soluble impurities which could adsorb back onto the solid surface when the solvent evaporates.

Disadvantages: The force of suction may draw fine crystals through the filter paper pores, leading to a quantity of material that cannot be recovered from the filter paper, and possibly an additional quantity that is lost in the filtrate. This method therefore works best with large crystals. On small scales, the loss of material to the filter paper and filtrate is significant, and so other methods are recommended for microscale work.

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. In the case of crystallization, the liquid may contain impurities that can reincorporate into the solid if not removed. To rinse a suction-filtered solid, the vacuum is removed and a small portion of cold solvent is poured over the solid the " filter cake ".

In the case of crystallization, the same solvent from the crystallization is used. The solid is then delicately slushed around in the solvent with a glass rod, and the vacuum is reapplied to remove the rinse solvent.

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.

During the entire chromatography process the eluent is collected in a series of fractions. The composition of the eluent flow can be monitored and each fraction is analyzed for dissolved compounds, e. Colored compounds or fluorescent compounds with the aid of an UV lamp can be seen through the glass wall as moving bands. Chelation Agent Many essential biological chemicals are chelates.

Chelates play important roles in oxygen transport and in photosynthesis. Furthermore, many biological catalysts enzymes are chelates. In addition to their significance in living organisms, chelates are also economically important, both as products in themselves and as agents in the production of other chemicals.

A chelate is a chemical compound composed of a metal ion and a chelating agent. A chelating agent is a substance whose molecules can form several bonds to a single metal ion. In other words, a chelating agent is a multidentate ligands with more than one bonded atom ligand.