Gravity filtration funnel

If you find yourself with a flask full of hot solvent, your product dissolved in it, along with all sorts of trash, this is for you. You ll need more hot solvent, a ringstand with a ring attached, possibly a clay triangle, some filter paper, a clean, dry flask, and a stemless funnel. Here s how gravity filtration works. 

Fig. 45 A wire triangle holding a small funnel in a large iron ring for gravity filtration.

Vacuum filtration involves carrying out filtration under reduced pressure and provides a faster method of separating a precipitate from a filtrate than traditional gravity filtration methods. A Buchner, Hirsch or sintered glass funnel can be used during vacuum filtration. 

The goal of gravity filtration is to remove solids from a liquid and obtain a liquid without solid particulates. Filter paper is folded, placed in a funnel on top of a flask, and wetted with the solvent to seal it to the funnel. Next the mixture is poured through, and the solid-free liquid is collected from the flask. 

Solids are easily washed by passing water, or the desired solvent over the solid product, which is contained in the filter funnel. For washing solids in this way, vacuum filtration should be used. Washing solids in this way using gravity filtration is a long and time consuming process. Obviously, do not wash the filtered-off solid with any liquid that reacts with, or dissolves the solid product. 

The key to successful gravity filtration is the fluted filter paper. A fluted filter paper decreases the area of contact between the filter paper and the funnel, thus allowing rapid filtration. If you use traditional cone-folded filter paper, note that all sides of the paper are touching the sides of the funnel and on half the filter paper the liquid has to pass through three thicknesses of paper, all of which slow the rate of filtration. Slow filtration can lead to disaster in hot filtration during recrystallization (p. 100). 

The usual procedure for decolorization involves the addition of a small amount of charcoal to a hot, nearly saturated solution of the compound to be purified. This is followed by a period of heating and gravity filtration to remove the charcoal. Gravity filtration is required because charcoal will usually pass through filter paper if vacuum filtration is employed. It is important to minimize crystalfization of the compound during the filtration, and this may conveniently be done by inserting the stem of a short-stemmed filter funnel into the neck of the flask in which the solution is being heated. The hot vapors condense in the funnel and heat it. 

Set up your filtering apparatus. If you are using a Buchner funnel for vacuum filtration or a glass funnel for gravity filtration, follow the setup procedure under Filtration-Technique Option. ... 

Refer to page 764 to set up a filtering apparatus, either a Buchner funnel or a gravity filtration, depending on what equipment is available. 

Fig. 59 The gravity filtration setup with a funnel that fits the iron ring.

Procedures for gravity filtration are illustrated in FIGURE 1.2. Support the funnel on an iron ring attached to a ring stand, and place a beaker under the funnel so that the stem of the funnel touches the side of the beaker. Pour the suspension onto the filter paper. It is best to pour down a glass rod held in a vertical position against the lip of the beaker with its lower end close to the filter. Never fill the filter with liquid up to the top of the paper. Use a stirring rod or rubber policeman, if... 

The filter cone is prepared as indicated in Figure 8.1. It is then placed into a funnel of an appropriate size. With filtrations using a simple filter cone, solvent may form seals between the filter and the funnel and between the funnel and the lip of the receiving flask. When a seal forms, the filtration stops because the displaced air has no possibility of escaping. To avoid the solvent seal, you can insert a small piece of paper, a paper clip, or some other bent wire between the funnel and the lip of the flask to let the displaced air escape. As an alternative, you can support the funnel by a clamp fixed above the flask rather than placed on the neck of the flask. A gravity filtration using a filter cone is shown in Figure 8.2. 

Place 0.25 g of fhe anhydrous alcohol in a dry tesf fube and add 0.25 mL of phenylisocyanafe ( -naphthylisocyanafe for a phenol). If fhe compound is a phenol, add 1 drop of pyridine fo cafalyze fhe reacfion. If the reaction is not spontaneous, heat the mixture in a hot water bath (90°C) for 5-10 minufes. Cool the test tube in a beaker of ice, and scrafch fhe fube wifh a glass rod fo induce crystallization. Decant the liquid from the solid product or, if necessary, collecf fhe product by vacuum filtration. Dissolve the product in 2.5-3 mL of hof ligroin or hexane, and filter the mixture by gravity (preheat funnel) fo remove any unwanted and insoluble di-phenylurea present. Cool the filtrate to induce crystallization of the urethane. Collect the product by vacuum filtration. 

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