Ask for the question about the pressure reducing filter device, that is, the Brinell funnel

Is it the type of question below?

The mixed solution of sodium nitrate and potassium chloride of a certain concentration is heated to boiling, and the crystals are precipitated, filtered while hot, and the crystals A are separated, and the above filtrate is cooled to room temperature, and the crystals are precipitated (see below for the solubility table of the relevant substances).

The main ingredient of a is , and the impurities contained in it are

The main component of b is , and the impurities contained are:

Rinsing crystals with a small amount of hot water is also a method of removing impurities, and this method is suitable for removing impurities (filling) for crystals"a"or"b"), which is commonly used to purify another crystal.

Heated to boiling, crystals precipitate"The main experimental instruments required are ,"Strain while hot"The method often taken is:

Analysis] This question examines the relevant experiments of crystallization, and students are easily affected by fixed thinking, and directly judge according to the solubility of nano3 and kcl at different temperatures: the solubility of kcl is smaller than that of nano3 at high temperatures, and the solubility of kcl is less than that of nano3 at high temperatures, and the crystallization by evaporation is kcl, and the crystallization by cooling should be nano3In fact, there is an equilibrium in the solution as follows:

nano3+kcl nacl+kno3, heated to boiling to precipitate NaCl with less solubility, and cooling crystallization to precipitate Kno3 with very small solubility at low temperature

Answer: A is NaCl and the impurity is Kno3; B is Kno3 and the impurity is NaClA (because of the high solubility of KNO3 in hot water, NaCl contains impurities KNO3 can be washed with hot water), recrystallization (KNO3 contains impurities NaCl can be removed by multiple crystallization) Alcohol lamp, evaporation dish, glass rod.

Filtration while hot can be thought of from reducing the time of filtration and maintaining the temperature at the time of filtration, and the method often taken"Suction filtration with a preheated Brinell funnel".

When the diameter of the filter paper is larger than the diameter of the bottom of the Brinell funnel, the filter paper cannot be directly attached to the bottom of the funnel, and the excess filter paper edge will wrinkle and create a gap between the bottom of the funnel and the edge of the funnel, so that the solution can go.

The principle of suction filtration is often examined, why the suction filter device is used, the role of the safety bottle, and the installation of the two glass catheters that enter the safety bottle (that is, which side is long, which side is short?). ）

I'm really embarrassed, it's been two years, I've almost forgotten, I remember that there is one in the computer, how do I want to find it, but I can't find it. If you search for the 09 or 10 college entrance examination mock science comprehensive Zhejiang paper, there should be a similar problem.

Suction filter device operation steps:

1. Set up the device according to the figure below, and pad the filter paper on the flat-bottomed funnel (also known as Brinell funnel);

2. As shown in the figure below, connect A Brinell funnel, B suction filter bottle, C safety bottle (pressure reducing device) and air extraction pump to form a suction filter device.

3. Turn on the switch of the suction pump, pour in the solid-liquid mixture, and start the suction filtration. Under the action of the suction force generated by the water pump, the air inside the suction filter bottle will be pumped out, so that negative pressure is generated in the suction filter bottle, so that the pressure difference between the top of the flat-bottomed funnel and the suction filter bottle is generated, and the pressure above the flat-bottomed funnel is greater than the pressure in the suction filter bottle.

When the substance to be filtered is poured into the flat-bottomed funnel, under the pressure of the air above the flat-bottomed funnel, the substance with a particle size smaller than the filter paper enters the suction filter bottle through the filter paper, and the substance with a particle size greater than the filter paper remains on the filter paper of the funnel.

Notes:

1. When installing the instrument, the lower end of the funnel pipe should be inclined towards the branch nozzle. But don't get too close so that the filtrate doesn't get pumped away.

2. When the filtered solution is strongly acidic, alkaline or oxidizing, glass fiber should be used instead of filter paper or glass sand funnel instead of Brinell funnel.

3. It is not advisable to filter the colloidal precipitate and the precipitate with too small particles, because the colloidal precipitate is easy to penetrate the filter paper, and the precipitate with too small particles is easy to form a dense precipitate on the filter paper, and the solution is not easy to penetrate.

4. In the process of suction filtration, when there is a crack in the solid layer in the funnel, it should be pressed with something like a glass plug to plug the crack. If it is not compressed, it will also reduce the suction efficiency.

5. When stopping the suction filter, first unscrew the stopcock on the safety bottle to restore the normal pressure, and then turn off the suction pump.

If the filter paper is larger than the porcelain surface of the funnel, the filter paper will be folded, so that the filtrate will be sucked into the bottle from the edge of the filter paper during the filtration, resulting in crystal loss.

The correct operation is: trim the filter paper so that it is slightly smaller than the Brinell funnel, but cover all the holes, and moisten the filter paper with distilled water dropwise, and slightly open the suction valve to make the filter paper and the funnel tightly connected.

After wetting the filter paper, part of the filtrate can be poured into the water circulation pump first, and the vacuum level can be adjusted by the two-way piston on the buffer bottle. At the beginning, the vacuum degree can be lower, so that the filter paper will not be broken, and the remaining solution will be poured in after the filter cake has been closed and sold a layer, and the vacuum degree can be gradually increased until it is "dry".

The precipitated material cannot be effectively and quantitatively separated.

The user must fix the suction filter bottle on the iron frame table, so as not to spill the product during the operation, when cutting the filter paper, the size is just enough to cover the hole of the Brinell funnel, too large and too small will make the solid leak down.

If the system of suction filtration contains water, the filter paper must be a thicker filter paper, otherwise the filter paper will be broken, so as to achieve the effect of separation.

It may cause the filtrate to flow down without passing through the filter paper, which will cause the loss of solids or make the filtrate impure.

If the inner diameter of the Brinell funnel is exceeded, the gap between the filter paper and the funnel wall cannot be completely fitted, which will lead to the liquid being directly pumped out from the gap between the filter paper and the funnel wall during suction filtration, and the purpose of filtration cannot be achieved.

The questions that will arise are:

The precipitated material cannot be effectively and quantitatively separated.

Quite simply, solids will enter the filtrate and will also slow down filtration.

Vacuum filtration, also known as suction filtration, suction filtration, is the use of vacuum pump or air pump to pump out the air in the suction filter bottle to produce negative pressure, so that the filtration speed is accelerated, the vacuum filtration device is composed of a vacuum pump, a Brinell funnel, and a suction filter bottle.

1) Cut the filter paper by folding the filter paper in half twice or three times, so that the tip coincides with the center of the funnel, and the inner diameter of the funnel is used as the standard to make a mark. Cut the filter paper into a fan shape along the mark, open the filter paper, and trim it slightly if it is not round. Put it in the funnel and see if it's the right size.

If the filter paper is slightly larger than the inner diameter of the funnel, cut it smaller to make the filter paper slightly smaller than the inner diameter of the funnel, but it can cover all the porcelain holes. If the filter paper is large, the edge of the filter paper can not be close to the funnel and produce a gap, and the precipitation passes through the gap during filtration, resulting in the precipitation and the solution cannot be separated; The air passes through the gap, and the negative pressure can not be generated in the suction filter bottle, so that the filtration speed is slow and the precipitation is not dry. If the filter paper is small and cannot cover all the porcelain holes, it cannot be filtered.

Therefore, cutting a suitable filter paper is the key to successful vacuum filtration.

2) Stick to the filter paper Moisten it with a small amount of water, and gently press the filter paper with a clean hand or glass rod to remove the gaps, so that the filter paper sticks to the funnel. Place the funnel into the suction filter bottle and plug the stopper tightly. Note that the tip of the funnel neck is on the opposite side of the branch.

Turn on the switch, connect the rubber tube, and the filter paper will fit snugly to the bottom of the funnel. If there is a gap, be sure to remove it.

3) Filtration When filtration, the solution is generally first, and then the precipitate or crystals are transferred, so that the filtration speed is accelerated. When transferring the solution, guide it with a glass rod and pour the solution in no more than 2 3Use a glass rod to transfer the crystals to the bottom of the beaker and then to the funnel as much as possible.

If the transfer is not clean, you can add a small amount of filtrate in the filter flask, stir and pour at the same time, and let the filtrate bring out the crystals. Continue to suction until the crystals are dry, using a clean, dry stopper to press the crystals to speed them dry, but don't forget to remove the crystals from the stopper.

Suction leaching

The air pump is used to reduce the pressure in the suction filter bottle to achieve the purpose of solid-liquid separation.

Installations: Buchner Funnel, Suction Flask, Hose, Air Pump, Filter Paper.

Process: 1. Install the instrument, check whether the connection between the cloth funnel and the suction filter bottle is tight, and whether the connection port of the suction pump is leaking;

2. Trim the filter paper so that it is slightly smaller than the cloth funnel, but cover all the holes, and add distilled water dropwise to make the filter paper and the funnel tightly connected;

3. Transfer the solid-liquid mixture to the filter paper;

4. Turn on the suction pump switch and start the suction filtration.