I. Purpose of the test
1, familiar with distillation to separate the mixture.
2, master the method of determining the boiling point of compounds.
Second, the test principle
1, the principle of determining the boiling point of substances by micro method.
2. Distillation principle.
Third, test instruments and drugs.
Round bottom flask, thermometer, distillation head, condenser, tail pipe, conical flask, electric furnace, heating jacket, measuring cylinder, beaker, capillary tube, rubber band, hob, zeolite, chloroform and industrial alcohol.
Four. Test steps
1, alcohol distillation
(1) charging Take a dry round-bottomed flask, add about 50 ml of industrial alcohol, and add some zeolite in advance.
(2) Before heating, slowly introduce cold water into the cooling tube, open the electric heating jacket for heating, slowly increase the fire power to make it boil, then adjust the fire power to keep the temperature constant, collect the fraction, and measure the volume of ethanol.
Determination of boiling point by tracer method in distillation unit diagram
2, micro method to measure the boiling point
Add 8- 10 drops of chloroform to a small test tube, with the open end of the capillary tube facing down, stick the test tube next to the mercury ball of the thermometer, tie it tightly with a rubber band, immerse it in water, and heat it slowly. When the temperature reaches the boiling point, bubbles will appear at the capillary opening. At this time, stop heating and observe the temperature carefully until the last bubble wants to emerge from the opening and return to the inner tube. This is the boiling point.
Verb (abbreviation of verb) test data processing
Six, thinking about the problem
1, distillation, why can you put zeolite to prevent boiling? What should I do if I find no zeolite added after heating?
The surface of zeolite is uneven, which can produce gasification center and gasify the solution. When boiling, the gas produced is relatively uniform and difficult to boil. If you forget to add zeolite, stop heating first, and then add zeolite when there are no bubbles.
2. The water flowing to the condenser tube is from bottom to top, and vice versa. How to prevent the side pipe from breaking when putting the rubber pipe into the side pipe of the condenser?
The water in the condenser tube flows from the bottom to the top, not the other way around. Because the condenser tube can't be filled with water, it may bring two consequences: First, the condensation effect of gas is not good.
Second, the inner tube of the condenser tube may burst. When the rubber tube is inserted into the side tube of the condenser tube, it can be lubricated with water first to prevent the side tube from breaking.
3. Determine the boiling point by micro method, and take the instantaneous temperature of the last bubble as the boiling point of the compound. Why? Boiling point: the temperature at which the saturated vapor pressure of a liquid is equal to the external pressure.
At the moment when the last bubble is about to retract into the inner tube, the pressure in the tube is equal to the outside, so the temperature at this time is the boiling point of the compound.
Seven, equipment problems:
1) Select an instrument with appropriate capacity: the liquid volume should match the instrument, and the liquid volume in the bottle should not be less than 1/3 and not more than 2/3 of the bottle volume.
2) Location of thermometer: The upper line of the mercury ball of thermometer should be aligned with the lower line of the side tube of distillation head.
3) Receiver: There are two receivers, one receiving the low score and the other receiving the product score. A conical flask or a round bottom flask can be used. When distilling flammable liquids (such as ether), a rubber pipe should be connected to the branch pipe of the lead pipe to lead the tail gas to the water tank or outdoors.
4) Instrument installation steps: generally, from bottom to top, from left (head) to right (tail), it is easy first, then difficult, and then assembled one by one. The distillation unit is strictly prohibited to be installed as a closed system; When disassembling the instrument, it is the opposite, from tail to head and from top to bottom.
5) Distillation can separate liquids with different boiling points, but the boiling points of each component differ by at least 30℃.
6) If the boiling point of the liquid is higher than 140℃, use air to condense the tube.
7) For simple distillation, after installation of the device, condensed water should be introduced before heating.
8) The capillary port is downward.
9) Micro-method determination should pay attention to:
First, the heating should not be too fast and the measured liquid should not be too little to prevent the liquid from completely vaporizing;
Second, the air in the boiling point tube should be as clean as possible. Before the formal determination, let a large number of bubbles emerge from the boiling point inner tube in order to bring out air;
Third, observation should be meticulous and timely. Repeat several times, and the error is not more than 65438 0℃.
Experiment 2 recrystallization and filtration
I. Purpose of the test
1, learn the principle and method of recrystallization and purification of solid organic matter.
2. Learn the operation of suction filtration and thermal filtration.
Second, the test principle
The solubility of each component in a mixture is different in a certain solution or at different temperatures in the same solution to distinguish them.
Third, test instruments and drugs.
Circulating water vacuum pump, suction bottle, Buchner funnel, beaker, electric furnace, asbestos net, glass rod, filter paper, benzoic acid, activated carbon and balance.
Fourth, the test steps
1. Weigh 3g of acetanilide, put it into a 250ml beaker, add 80ml of water, and heat it to boiling. If it does not dissolve, add a proper amount of hot water, stir and heat until it boils.
2. After a little cooling, add an appropriate amount of activated carbon (0.5- 1g) to the solution, boil for 5- 10 minutes, and filter while it is hot.
3. Put the filtrate into ice water for crystallization, and flatten the obtained crystals. Filtering again, and weighing the crystallization mass m.
Verb (abbreviation for verb) test data
Questions and answers of intransitive verbs
1. Decolorization with activated carbon Why wait until the solid is completely dissolved before adding it? Why not add it when the solution is boiling?
(1) Only after the solid sample is completely dissolved can we see whether the solution has color and the depth of color, so as to decide whether or how much activated carbon should be added;
(2) If the solid sample is not completely dissolved, adding activated carbon will make the solid sample not completely dissolved (activated carbon will absorb some solvents), and the amount of purified substances contaminated by activated carbon will also increase;
(3) Due to the addition of black activated carbon, the solution turns black, and it is impossible to observe whether the solid sample is completely dissolved.
The above three reasons will lead to the reduction of the recovery rate of pure products.
When using activated carbon, it is not allowed to add activated carbon to boiling solution to avoid boiling and splashing.
2. What should I pay attention to when washing the filter cake with solvent on the Buchner funnel?
Do not loosen the filter paper when washing the filter cake for the first time.
Second, check the air tightness, and keep the oblique split of the Buchner funnel and the branch pipe of the suction bottle away.
Third, the size of the filter paper should be appropriate. If it is too big, it will leak, and it is not close to the funnel, so it is not easy to drain.
3. Advantages of suction filtration: ① Fast filtration and washing speed; ② The liquid-solid separation is relatively thorough; ③ The filtered solid is easy to dry.
4. What happened when the filter paper was larger than the porcelain hole surface of the Buchner funnel?
Answer: If the filter paper is larger than the hole surface of funnel porcelain, the filter paper will fold, so the filtrate will be sucked into the bottle from the edge of the filter paper during suction filtration, resulting in crystal loss. So it can't be big, just cover the porcelain hole.
5, at the end of the decompression, should first through the atmosphere, and then turn off the pump, in order to prevent backward suction.
6. The purpose of adding activated carbon in the experiment is decolorization and adsorption. But don't add too much, too much will adsorb the product. Nor can it be added when boiling, so as to avoid the solution boiling out of the container. The dosage is 1%-3%.
Experimental preparation of tribenzoic acid
First, the experimental purpose
1, learn the oxidation reaction on benzene ring branch.
2. Master the methods of vacuum filtration and recrystallization purification.
Second, the experimental principle
Third, experimental instruments and drugs.
Balance, measuring cylinder, round bottom flask, condensing tube, electric furnace, Buchner funnel, suction filter bottle, toluene, potassium permanganate, concentrated hydrochloric acid, zeolite and activated carbon.
Fourth, the experimental steps
1, put 2.7ml toluene and 100ml distilled water in the flask, put a condenser tube on the bottle mouth and heat it to boiling. 8.5g of potassium permanganate was added in batches through the upper opening of the condenser tube. Pour the potassium permanganate attached to the inner wall of the condenser tube into the flask with 25 ml of water, and continue to boil until the toluene layer disappears and oil beads no longer appear in the reflux liquid.
2. Filter the reaction mixture while it is hot, wash the filter residue with a little hot water, combine the filtrate and washing liquid, cool in a cold water bath, and then acidify with concentrated hydrochloric acid until benzoic acid is completely precipitated (if the filtrate is purple, add sodium bisulfite to remove it).
3. Filter the obtained filtrate with a Buchner funnel, fully dissolve the obtained crystal in boiling water (if there is color, add activated carbon to remove it), then filter while it is hot to remove insoluble impurities, put the filtrate in an ice water bath for recrystallization, suction filtration, drying and weighing.
Reflux device diagram
Verb (abbreviation of verb) experimental data processing
Six, thinking about the problem
1, after the reaction, if the filtrate is purple. What is the effect of adding sodium bisulfite?
Sodium bisulfite can react with potassium permanganate, consuming excessive potassium permanganate to produce manganese dioxide, and the purple color of the solution fades, resulting in brown precipitation.
2. Briefly describe the operation process of recrystallization.
Selecting solvents → dissolving solids → removing impurities → precipitating crystals → collecting and washing crystals → drying crystals.
1. Dissolve the substance to be recrystallized in a suitable solvent to prepare a supersaturated solution.
2. If the material to be recrystallized contains colored impurities, activated carbon can be added to boil and decolorize.
3. Filter while it is hot to remove insoluble matter and activated carbon.
4. Cooling the filtrate to precipitate crystals from the supersaturated solution, while soluble impurities remain in the solution.
5. Filtering under reduced pressure, separating the crystal from the mother liquor, and washing the crystal to remove the mother liquor adsorbed on the surface of the crystal.
3. How to avoid bottle mouth adhesion by adding potassium permanganate during the preparation of benzoic acid? What is the black solid that sticks to the bottle wall after the experiment? How to remove it?
Answer: You can use a thick-necked funnel or fold the weighing paper into a trumpet, and add tiny solids into the bottle. The black solid sticking to the wall is manganese dioxide. The simple removal method is: adding dilute sodium sulfite solution and gently shaking to remove manganese dioxide. Its principle is redox mechanism.
Seven, note:
1, be sure to wait for the reaction liquid to boil (potassium permanganate is only soluble in water, but insoluble in organic solvents), and then add potassium permanganate in batches to avoid violent reaction from spraying from the upper end of the reflux pipe.
2. In the preparation of benzoic acid, the filtrate obtained by suction filtration is purple because it contains potassium permanganate, which can be removed by adding sodium bisulfite.