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1. Six principles in the operation of chemistry experiments in middle schools
By mastering the following seven principles related to the sequence of operations, you will be able to correctly answer the "Experimental Procedure Judgment Question".
1. The "bottom-up" principle. Taking the Cl2 laboratory method as an example, the assembly of the generator sequence is as follows: put the iron frame→ set the alcohol lamp→ fix the iron ring → asbestos net according to the position of the alcohol lamp→ fix the round-bottom flask.
2. The "left-to-right" principle. The assembly complex follows a left-to-right order. The assembly sequence of the above device is as follows: generator device→ gas collector cylinder → beaker.
3. The principle of "solid first". In the example above, the reagent MnO2 in the flask should be loaded before the flask is fixed to avoid damaging the flask when the solids are placed. In summary, solid reagents should be added to the appropriate container before fixation.
4. The principle of "liquid after adding". Liquid medicines are added after the flask has been fixed. As in the example above, concentrated hydrochloric acid should be added slowly in the separating funnel after the flask has been fixed.
5. The principle of a priori air tightness (before loading the medicine port).
6. The principle of lighting the alcohol lamp after all devices are installed (after all devices are installed).
2. What are the three types of thermometer use in middle school chemistry experiments and which experiments require thermometers?
1. Measure the temperature of the reaction mixture: This type of experiment requires the accurate temperature of the reaction mixture, therefore, a thermometer should be inserted into the middle of the mixture. (1) Measure the solubility of the substance. (2) Laboratory-made ethylene.
2. Measure the temperature of vapor: This type of experiment is mostly used to measure the boiling point of a substance, because the temperature of the liquid and the vapor is the same when the liquid is boiling, so only the temperature of the vapor needs to be measured. (1) Laboratory distillation of petroleum. (2) Determination of the boiling point of ethanol.
3. Measuring the temperature of the water bath: In this type of experiment, as long as the temperature of the reactants is kept relatively stable, the water bath is used to heat it, and the thermometer is inserted into the water bath. (1) The reaction of the effect of temperature on the reaction rate. (2) nitrification of benzene.
3. What are the common experiments that need to be stuffed with cotton?
加热KMnO4制氧气；制乙炔和收集NH3
Its functions are:
Prevent KMnO4 powder from entering the catheter;
Prevent foam from the experiment from pouring into the catheter;
Prevent ammonia convection with air to shorten the time it takes to collect NH3.
4. 10 methods for separation and purification of common substances
1. Crystallization and recrystallization: the solubility of the substance in the solution varies greatly with temperature, such as NaCl and KNO3.
2. Distillation cooling method: the difference in boiling point is large. In ethanol (water): add freshly made CaO to absorb most of the water and then distill.
3. Filtration method: soluble and insoluble.
4.: SiO2 (I2)。
5. Extraction method: the solubility of the solute is different in two immiscible solvents, and the solute is transferred from the solution with low solubility to the solvent with high solubility, such as CCl4 to extract I2 in water.
6. Dissolution method: Fe powder (A1 powder): Al is dissolved in excess NaOH solution and filtered and separated.
7. Addition method: convert impurities into the required substances: CO2 (CO) can be passed through the hot CuO; CO2 (SO2) can be passed through NaHCO3 solution.
8. Absorption method: remove the gas impurities in the mixed gas, and the gas impurities must be absorbed by the drug: the N2 (O2) mixed gas can absorb O2 through the copper mesh.
9.转化法：两种物质难以直接分离，加药品变得容易分离，然后再还原回去：Al(OH)3，Fe(OH)3：先加足量的NaOH溶液把Al(OH)3溶解，过滤，除去Fe(OH)3，再加酸让NaAlO2转化成A1(OH)3。
5. There are 10 commonly used methods to remove impurities
1. Impurity conversion method: to remove phenol in benzene, sodium hydroxide can be added to convert phenol into sodium phenol, and sodium phenol can be easily soluble in water to separate it from benzene. To remove NaHCO3 from Na2CO3, heating can be used.
2. Absorption washing method: To remove a small amount of hydrogen chloride and water mixed in carbon dioxide, the mixed gas can pass through the solution of saturated sodium bicarbonate first, and then through concentrated sulfuric acid.
3. Precipitation filtration method: to remove a small amount of copper sulfate mixed in ferrous sulfate solution, add excess iron powder, and after full reaction, filter to remove insoluble matter to achieve the purpose.
4. Heating sublimation method: If you want to remove the sand in iodine, you can use this method.
5. Solvent extraction method: If you want to remove a small amount of bromine contained in water, you can use this method.
6. Solution crystallization method (crystallization and recrystallization): If you want to remove a small amount of sodium chloride in sodium nitrate solution, you can use the different solubility of the two to reduce the temperature of the solution, so that the sodium nitrate crystallization is precipitated to obtain pure sodium nitrate.
7. Fractional distillation method: If you want to remove a small amount of alcohol in ether, you can use multiple distillations.
8. Liquid separation method: If you want to separate liquid mixtures with different densities and immiscible with each other, this method can be used, such as separating benzene and water.
9. Dialysis method: If you want to remove ions in colloid, this method can be used. Such as the removal of chloride ions in iron hydroxide colloids.
10. Comprehensive method: If you want to remove impurities in a substance, you can use the above methods or a combination of methods.
6. 15 cases of "no" in the basic operation of chemical experiments
1. Drugs in the laboratory should not be touched by hand; Don't put your nose at the mouth of the container to smell the gas, and don't taste the crystallization.
2. After the experiment, the leftover drugs should not be discarded, and should not be put back into the original bottle (except for active metal sodium, potassium, etc.).
3. When taking liquid medicines, open the cork and do not put it on the table; The label on the bottle should be towards the palm of the hand, not downward; The label should not be inward-facing when put back in.
4. If the skin is accidentally sprinkled with concentrated H2SO4, it should not be washed with water first, but should be quickly wiped off with a cloth according to the situation, and then rinsed with water; If there is acid or alkali splashed in the eyes, do not rub the eyes with your hands, and you should find a way to deal with them in time.
5. When weighing drugs, do not put the weighed items directly on the tray; It is also not possible to put the weighing object on the right plate; Don't use your hands to pick up the code when adding codes.
6. When adding liquid with a dropper, do not put the dropper into the graduated cylinder (test tube) or touch the wall of the cylinder (test tube wall).
7. When adding alcohol to the alcohol lamp, it shall not exceed 2/3 of the volume of the alcohol lamp, and shall not be less than 1/3 of the volume.
8. Do not use a lit alcohol lamp to point another alcohol lamp; Do not blow with your mouth when extinguished.
9. When heating the substance, the inner flame and flame center of the alcohol lamp shall not be used.
10. When heating the test tube, do not press your thumb on the short handle; Do not point the mouth of the test tube to yourself or others; The volume of liquid should generally not exceed 1/3 of the volume of the test tube.
11. Don't forget to put an asbestos net when heating the flask.
12. After heating with a crucible or evaporation dish, do not take it back directly by hand, and use a crucible plier to clamp it.
13. When using a glass container for heating, do not make the bottom of the glass container contact with the wick to avoid the container breaking. Glass containers that are burned very hot, do not rinse them with cold water or put them on the table top to avoid breaking.
14. When filtering liquid, the liquid level of the liquid in the funnel should not be higher than the edge of the filter paper, so as to avoid impurities from entering the filtrate.
15. When plugging the rubber stopper at the mouth of the flask, do not put the flask on the table and then stuff it into the stopper to avoid crushing the flask.
7. 22 cases in chemical experiments
1. When heating the test tube, it should be evenly heated first and then locally heated.
2. When collecting gas by drainage, take out the catheter and withdraw the alcohol lamp.
3. When preparing gas, first check the air tightness and then load the drug.
4. When collecting gas, drain the air in the device before collecting.
5. When diluting concentrated sulfuric acid, fill a certain amount of distilled water in the beaker first, and then slowly inject concentrated sulfuric acid along the wall of the beaker.
6.点燃H2、CH4、C2H4、C2H2等可燃气体时，先检验纯度再点燃。
7. When testing the halogen elements of halogenated hydrocarbon molecules, dilute HNO3 and then add AgNO3 solution to the hydrolyzed solution.
8. When testing NH3 (with red litmus test paper), Cl2 (with starch KI test paper), H2S [with Pb(Ac)2 test paper] and other gases, wet the test paper with distilled water before coming into contact with the gas.
9. When doing the reaction experiment between solid drugs, first grind separately and then mix.
10. When preparing FeCl3, SnCl2 and other easily hydrolyzable salt solutions, first dissolve in a small amount of concentrated hydrochloric acid, and then dilute.
11. When neutralizing the titration experiment, the burette washed with distilled water should be washed with the standard solution before the standard is installed; Rinse with the solution to be tested before pipetting the liquid; When the burette is reading, wait one or two minutes before reading; When observing the change in the color of the solution in the Erlenmeyer flask, wait for half a minute for the color to change before the titration endpoint.
12. During the flame color reaction experiment, each time you do it, the platinum wire should be dipped in dilute hydrochloric acid and burned on the flame until it is colorless, and then the next experiment should be done.
13. When reducing CuO with H2, first pass the H2 flow, then heat the CuO, remove the alcohol lamp after the reaction is completed, and then stop the H2 flow after cooling.
14. When preparing the dosage and concentration solution of the substance, first add distilled water to the scale line of the volumetric flask 1cm~2cm with a beaker, and then add water to the scale line with a rubber head dropper.
15. When installing the generator, the principle to be followed is: bottom-up, first left and then right or first down and then up, first left and then right.
16. If concentrated H2SO4 is accidentally sprinkled on the skin, dry it quickly with a cloth first, then rinse with water, and finally apply 3%-5% NaHCO3 solution. When stained with other acids, wash with water and then apply NaHCO3 solution.
17. When the lye is stained on the skin, wash it with water and then apply the boric acid solution.
18. Acid (or alkali) flows to the table, first add NaHCO3 solution (or acetic acid) to neutralize, then wash, and finally wipe with a cloth.
19. When testing whether sucrose, starch and cellulose are hydrolyzed, add NaOH solution to neutralize H2SO4 in the hydrolyzed solution, and then add silver ammonia solution or Cu(OH)2 suspension.
20. When using pH test paper, first dip the solution to be measured with a glass rod and apply it to the test paper, and then compare the color of the test paper with the standard color card to determine the pH.
21. When preparing and preserving Fe2+, Sn2+ and other salt solutions that are easy to hydrolyze and easily oxidized by air; First, boil the distilled water to drive away the O2, then dissolve, and add a small amount of the corresponding metal powder and the corresponding acid.
22. When weighing medicines, first put two sheets of paper of equal size and weight on the plate (corrosive drugs are placed in glassware such as beakers), and then put medicines. After heating, the medicine is cooled first and then weighed.
8. The placement method of the position of the catheter and funnel in the experiment
Catheters and funnels are used in many chemical experiments, so their correct placement in the experimental setup directly affects the effectiveness of the experiment, and the specific requirements vary from experiment to experiment. The following is a brief analysis and summary of the experimental diagrams in the experiment and chemistry textbook.
1. Conduit in gas generating device; The part of the container can only show a little rubber stopper or parallel to it, otherwise it will not be conducive to exhaust.
2. When collecting gas by exhausting air (both upward and downward), the catheter must be extended near the bottom of the gas collection cylinder or test tube. This facilitates the exhaustion of the air in the gas collector cylinder or test tube and collects the purer gas.
3. When collecting gas by drainage, the catheter only needs to reach the mouth of the gas collection cylinder or test tube. The reason is that "the amount of the catheter protruding into the gas collection cylinder and test tube does not affect the gas collection", but compared with the two, the former is easy to operate.
4. When conducting experiments on the reaction of gas with solution, the catheter should extend to the middle and lower part of the container containing the solution. This is conducive to the contact between the two and fully reacts.
5. When igniting H2, CH4, etc., and proving that water is generated, not only a large and cold beaker should be used, but also the catheter should be extended into 1/3 of the beaker. If the catheter is inserted too much into the beaker, the resulting droplets will quickly vaporize and no water droplets will be observed.
6. When conducting experiments in which one gas burns in another, the conduit of the ignited gas should be placed in the center of the gas collector cylinder containing the other gas. Otherwise, if it collides with the wall of the cylinder or gets too close, the high temperature generated by the combustion will cause the cylinder to burst.
7. When the vapor of the substance prepared by the heating method is condensed and collected in the test tube, the catheter mouth must always keep a certain distance from the liquid level of the liquid in the test tube to prevent the liquid from being sucked into the reactor through the catheter.
8. If it is necessary to directly dissolve water-soluble gases such as HCl and NH3 into water, a funnel must be inverted on the catheter and the edge of the funnel must be slightly immersed in the water surface to avoid the water being sucked into the reactor and causing the experiment to fail.
9. The catheter for air intake in the gas washing cylinder must be inserted into the middle and lower part of the solution to facilitate the full reaction of the impurity gas with the solution and remove it. The catheter that supplies air must be flush with the plug or slightly longer to facilitate exhaust.
10. When making H2, CO2, H2S and C2H2 and other gases, in order to facilitate the addition of acid or water, a long-neck funnel can be installed on the stopper of the container, and the funnel neck must be inserted below the liquid level to avoid air leakage.
11. When making Cl2, HCl, C2H4 gas, in order to facilitate the addition of acid, a funnel can also be installed on the plug of the reactor. However, since these reactions require heating, the funnel neck must be placed on top of the reaction solution, so the separating funnel is used.
9. Storage and retrieval of special reagents in 10 cases
1.Na, K: air isolation; Anti-oxidation, stored in kerosene (or liquid alkanes), (Li is sealed with paraffin). Take it with tweezers, cut it on the slide, suck the kerosene on the filter paper, and then put the remaining part into the kerosene.
2. White phosphorus: keep in water, anti-oxidation, and put in a cool and dark place. Take with tweezers and immediately put it in water with a long-handled knife to cut and filter paper to absorb the water.
3. Liquid Br2: toxic and volatile, contained in a grinding mouth bottle, and sealed with water. The cap is tight.
4.I2: Easy to sublimate, and has a strong pungent odor, should be kept in a wax sealed bottle, placed at a low temperature.
5. Concentrated HNO3, AgNO3: easy to decompose when exposed to light, should be kept in a brown bottle and placed in a low temperature and dark place.
6. Solid caustic soda: easy to deliquescent, should be stored in a dry large-mouth bottle that is easy to seal. The mouth of the bottle is tightly corked with a rubber stopper or closed with a plastic cap.
7.NH3•H2O：易挥发，应密封放低温处。
8.C6H6、、C6H5—CH3、CH3CH2OH、CH3CH2OCH2CH3：易挥发、易燃，应密封存放低温处，并远离火源。
9. Fe2+ salt solution, H2SO3 and its salt solution, hydrosulfuric acid and its salt solution: because it is easy to be oxidized by air, it is not suitable for long-term storage, and should be used and prepared.
10. Brine, lime water, silver ammonia solution, Cu(OH)2 suspension, etc., should be used with the mix, and cannot be placed for a long time.
10. There are 4 cases of experimental problems related to "0" in middle school chemistry
1. The scale at the top of the burette is 0.
2. The scale at the bottom of the graduated cylinder is 0 (it is not actually marked, and the bottom is 0).
3. The middle scale of the thermometer is 0.
4. The center value of the scale of the pallet balance is 0.
11. Gases that can be used for fountain experiments
NH3, HCl, HBr, HI and other gases that are easily soluble in water can be used for fountain experiments. If other gases are very soluble in a liquid (e.g., CO2 is soluble in caustic soda solution), fountain experiments can also be done.
12. 80 specific experiments of main experimental operations and experimental phenomena
1. Magnesium strips burn in the air: emit a dazzling bright light, emit a large amount of heat, generate white smoke and produce a white substance.
2. Charcoal burns in oxygen: it emits white light and releases heat.
3. Sulfur burns in oxygen: it emits a bright blue-purple flame that releases heat and produces a gas with a pungent odor.
4. Iron wire burns in oxygen: it burns violently, sparks shine in all directions, emit heat, and generate black solid matter.
5. Heating ammonium bicarbonate in the test tube: there is a pungent odor gas generation, and droplets are generated on the test tube.
6. Hydrogen burns in the air: The flame has a pale blue color.
7. Hydrogen burns in chlorine: it emits a pale flame that produces a lot of heat.
8. Copper oxide is reduced with hydrogen in the test tube: the black copper oxide becomes a red substance, and droplets are formed at the mouth of the test tube.
9. Reduce copper oxide powder with charcoal powder, so that the generated gas is passed into the clarified lime water, the black copper oxide becomes shiny metal particles, and the lime water becomes turbid.
10. Carbon monoxide burns in the air: It emits a blue flame that releases heat.
11. Add hydrochloric acid dropwise to a test tube containing a small amount of potassium carbonate solids: gas is generated.
12. Heat the copper sulfate crystals in the test tube: the blue crystals gradually turn into white powder, and there are droplets at the mouth of the test tube.
13. Sodium burns in chlorine gas: burns violently to produce a white solid.
14. Ignite pure chlorine gas and cover the flame with a dry cold beaker: a light blue flame is emitted, and droplets are generated on the inner wall of the beaker.
15. Add a silver nitrate solution acidified with nitric acid dropwise to the solution containing C1-, and a white precipitate is generated.
16. Add a barium chloride solution acidified with nitric acid dropwise to the solution containing SO42-, and a white precipitate is generated.
17. A strip of rusty iron nails is put into a test tube containing dilute sulfuric acid and heated: the rust gradually dissolves, the solution is light yellow, and gas is generated.
18. Add sodium hydroxide solution dropwise to copper sulfate solution: there is a blue flocculent precipitate generated.
19. Cl2 is passed into a colorless KI solution, and a brown substance is produced in the solution.
20. Add sodium hydroxide solution dropwise in ferric chloride solution: reddish-brown precipitate is generated.
21. Add a small amount of water to the test tube containing quicklime: the reaction is violent, emitting a lot of heat.
22. Immerse a clean iron nail in copper sulfate solution: there is a red substance attached to the surface of the iron nail, and the color of the solution gradually becomes lighter.
23. Insert the copper sheet into the mercury nitrate solution: there is a silvery-white substance attached to the surface of the copper sheet.
24. Inject a concentrated sodium carbonate solution into a test tube containing lime water: a white precipitate is generated.
25. Water is added after the thin copper wire is burned in chlorine gas: brown smoke is generated, and a green solution is formed after adding water.
26. Mixed gas of hydrogen and chlorine irradiated by strong light: rapid reaction and explosion.
27. Red phosphorus burns in chlorine gas: white smoke is generated.
28. Chlorine meets wet colored cloth strips: The color of the colored cloth strips recedes.
29. Heating a mixture of concentrated hydrochloric acid and manganese dioxide: there is a yellow-green pungent odor gas generated.
30. Heating the mixture of sodium chloride (solid) and sulfuric acid (concentrated): fog generation and pungent odor generation.
31. Add silver nitrate solution dropwise to sodium bromide solution and then add dilute nitric acid: there is a light yellow precipitate generated.
32. Add silver nitrate solution dropwise to potassium iodide solution and then add dilute nitric acid: yellow precipitate is generated.
33. I2 encounters starch and generates a blue solution.
34. Fine copper wire burns in sulfur vapor: After the fine copper wire turns red, it forms a black substance.
35. Iron powder is mixed with sulfur powder and heated to red hot: the reaction continues, releasing a large amount of heat to form a black substance.
36. Incomplete combustion of hydrogen sulfide gas (covering the evaporation dish over the flame): the flame is light blue (there is a yellow powder at the bottom of the evaporation dish).
37. Complete combustion of hydrogen sulfide gas (dry cold beaker over the flame): the flame is light blue, generating a gas with a pungent odor (generated by droplets on the inner wall of the beaker).
38. Mix hydrogen sulfide and sulfur dioxide in the gas collection cylinder: yellow powder is generated on the inner wall of the cylinder.
39. Sulfur dioxide gas is reheated after passing into the magenta solution: the red color fades away, and it returns to its original color after heating.
40. Excess copper is put into a test tube containing concentrated sulfuric acid, heated, the reaction is completed, and water is added after the solution is cooled: gas with a pungent odor is generated, and the solution is sky blue after adding water.
41. Heating a test tube containing concentrated sulfuric acid and charcoal: gas is generated, and the gas has a pungent odor.
42. Sodium burns in the air: the flame is yellow, producing a yellowish substance.
43. Sodium is put into water: the reaction is intense, the sodium floats on the water surface, and a large amount of heat is released to dissolve the sodium into a small ball swimming on the water surface, and there is a "snort" sound.
44. Drop water into a test tube containing sodium peroxide solids, and extend a strip of wood with Mars into the mouth of the tube: the strip rekindles.
45. Heat the sodium bicarbonate solid so that the generating gas passes into the clarified lime water: the clarified lime water becomes turbid.
46. Ammonia meets hydrogen chloride: there is a large amount of white smoke produced.
47. Heating a mixture of ammonium chloride and calcium hydroxide: a gas with a pungent odor is generated.
48. Heating a test tube containing solid ammonium chloride: white crystals are produced at the mouth of the test tube.
49. The concentrated nitric acid in the colorless reagent bottle is exposed to sunlight: the space in the bottle is brown, and the nitric acid is yellow.
50. Reaction between copper sheet and concentrated nitric acid: the reaction is intense, and reddish-brown gas is produced.
51. Copper sheet reacts with dilute nitric acid: colorless gas is produced at the lower end of the test tube, and the gas rises and gradually turns reddish-brown.
52. Dilute hydrochloric acid is added to sodium silicate solution, and a white gelatinous precipitate is produced.
53. Add magnesium sulfate solution to iron hydroxide colloid: the colloid becomes turbid. 54. Heating iron hydroxide colloid: the colloid becomes turbid.
55. Stick the lit magnesium strip into the gas cylinder containing carbon dioxide: it burns violently, and there is a black substance attached to the inner wall of the gas cylinder.
56. Add ammonia dropwise to the aluminum sulfate solution: a fluffy white flocculent substance is generated.
57. Add sodium hydroxide solution dropwise to ferrous sulfate solution: there is a white flocculent precipitate generated, which immediately turns to gray-green, and then turns to reddish-brown precipitate after a while.
58. Add KSCN solution to the solution containing Fe3+: the solution is blood-red.
59．向硫化钠水溶液中滴加氯水：溶液变浑浊。 S2-+Cl2=2Cl2-+S↓
60. Add a small amount of soap to natural water: the foam gradually decreases, and precipitation occurs.
61. Ignite methane in the air and dry a cold beaker over the flame: the flame is pale blue and droplets are produced on the inner wall of the beaker.
62. Mixed gas of photomethane and chlorine: yellow-green gradually lightens for a longer time, (there are droplets on the inner wall of the container).
63. Heat the mixture of ethanol and concentrated sulfuric acid (170 °C) and let the resulting gas pass into bromine water and into the acidic potassium permanganate solution: gas is generated, bromine water fades, and the purple color gradually becomes lighter.
64. Igniting ethylene in the air: The flame is bright, black smoke is produced, and heat is released.
65. Igniting acetylene in the air: The flame is bright, and thick smoke is produced, which releases heat.
66. Benzene burns in the air: the flame is bright and carries black smoke.
67. Ethanol burns in the air: The flame has a pale blue color.
68. Acetylene is passed into bromine water: Bromine water fades its color.
69. Pass acetylene into the acidic potassium permanganate solution: the purple color gradually lightens until it fades.
70. Benzene reacts with bromine under the condition of iron powder as a catalyst: a white mist is produced, and the product is oily and brownish.
71. Pour a small amount of toluene into an appropriate amount of potassium permanganate solution and shake: purple fades.
72. Put the sodium metal into a tube containing ethanol: there is a gas out.
73. Drop excess concentrated bromine water into a test tube with a small amount of phenol: a white precipitate is formed.
74. Drop a few drops of ferric chloride solution in a test tube containing phenol and shake: the solution appears purple.
75. Acetaldehyde reacts with silver ammonia solution in a test tube: a layer of bright substance is attached to the inner wall of a clean test tube.
76. In the case of heating to boiling, acetaldehyde reacts with freshly made copper hydroxide: there is a red precipitate generated.
77. Reaction of ethanol and acetic acid under suitable conditions: a transparent and fragrant oily liquid is generated.
78. Protein meets concentrated HNO3 solution: turns yellow. 79. Purple litmus solution meets alkali: turns blue.
80. Colorless phenolphthalein test solution meets alkali: turns red.
13. The wonderful use of water in experiments
1. Water seal: In middle school chemistry experiments, liquid bromine needs to be sealed with water, and a small amount of white phosphorus is stored in a jar filled with cold water. Liquid bromine is highly volatile and highly toxic, and its solubility in water is smaller and heavier than water, so it can also be sealed to reduce its volatilization.
2. Water bath: preparation of phenolic resin (boiling water bath); The preparation of nitrobenzene (50-60 °C), the hydrolysis of ethyl acetate (70~80 °C), the hydrolysis of sucrose (70~80 °C), and the determination of potassium nitrate solubility (room temperature ~ 100 °C) need to be controlled by a thermometer; The silver mirror reaction needs to be heated with a warm water bath.
3. Water collection: The drainage gas collection method can collect insoluble or insoluble gases in water, and there are O2, H2, C2H4, C2H2, CH4, NO in the middle school stage. Some gases have a certain solubility in water, but a substance can be added to the water to reduce their solubility, such as chlorine gas collected by the saturated brine method.
4. Water washing: The method of washing with water can remove some soluble impurities in insoluble gases, such as N02 impurities in NO gas.
5. Identification: Some substances can be identified by different solubility or density in water, such as: benzene, ethanol and three bottles of ethyl bromide without labeling colorless liquid, when using water to identify benzene floating on water, ethanol dissolved in water, and ethyl bromide sinking underwater. The use of soluble heat of dissolution, such as: sodium hydroxide, ammonium nitrate, sodium chloride, calcium carbonate, can be identified with water alone.
6. Leak detection: After the gas generator is connected, the principle of thermal expansion and cold contraction is applied, and water can be used to check whether it is leaking.
14. The order of dropping is different, and the phenomenon is different
1．AgNO3与NH3· H2O：
AgNO3 to NH3· H2O dropwise addition - no white precipitate at the beginning, then white precipitate is produced
NH3· H2O向AgNO3中滴加——开始有白色沉淀，后白色沉淀消失
2．NaOH与AlCl3：
NaOH was added dropwise to AlCl3 - a white precipitate began and disappeared later
AlCl3 was added dropwise to NaOH, which began without a white precipitate, and then produced a white precipitate
3.HCl与NaAlO2:
HCl was added dropwise to NaAlO2 - white precipitate at the beginning, and then the white precipitate disappeared
NaAlO2 is added dropwise to HCl - no white precipitate at first, and then white precipitate is produced
4. Na2CO3 and hydrochloric acid:
Na2CO3 is added dropwise to hydrochloric acid – bubbles begin and no bubbles are produced
Hydrochloric acid is added dropwise to Na2CO3 – no bubbles at first, then bubbles are produced
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