Techniques.
1. If excessive salt intake will harm human health, ** 3 5 g of salt per day is sufficient.
2. Pay attention to the purification of coarse salt:
When dissolving, coarse salt should be added gradually, and cannot be poured into a beaker at one time;
When filtration, if the filtrate is turbid, it should be re-filtered;
When evaporating, it is necessary to constantly stir with a glass rod to prevent liquid splashing caused by local overheating;
When there are more solids in the evaporation dish, the heating is stopped, and the liquid is evaporated with residual heat.
3. Key points in the chemical properties of salts.
Salt + metal New metal + new salt Pre-posterior (except K, Ca, Na), salt soluble;
Salt + Alkali New Salt + New Alkali Both salt and alkali must be soluble;
Salt + Salt New Salt + New Salt Both salts must be soluble.
4. Whether the reaction can be carried out: the conditions for the metathesis reaction are used.
5. For the concept and characteristics of metathesis reaction, it can be understood and remembered in connection with the essence of chemical reaction and the principle of dissolution. In addition, it is necessary to grasp the two key words of "compound" and "exchange of ingredients" in the concept.
6. In order to correctly write the chemical equation of metathesis reaction, it is also required to memorize the solubility table of common acids, alkalis and salts and correctly use the solubility of substances.
7. The reaction between acid, alkali and salt solution is generally formed by the exchange of components between two compounds, that is, the compounds participating in the metathesis reaction are ionized and dissociated into free-moving ions in the aqueous solution, and the ions are recombined into new compounds, so the reaction between acid, alkali and salt solutions is generally a metathesis reaction.
8. Solubility law of acid, alkali and salt:
Acids: The acids that you come into contact with in junior high school are water-soluble acids.
Alkali: Common alkalis only dissolve "potassium, sodium, barium, calcium, ammonium", that is, KOH, Naoh, BA(OH)2, Ca(OH)2, NH3·H2O are soluble in water.
Salt: potassium, sodium, ammonium and nitrate are all soluble in water; The only soluble carbonates in carbonates are potassium carbonate, sodium carbonate and ammonium carbonate; AGCL and BaSO4 are insoluble in neither water nor acid.
9. Pros and cons of chemical fertilizers and pesticides:
Positive side: Fertilizers and pesticides play an important role in increasing crop yields.
Harmful aspects: the irrational use of chemical fertilizers can bring many environmental problems; Pesticides are inherently toxic substances, which not only kill pests and diseases, but also bring pollution to the environment and harm to the human body.
10. Rational use of chemical fertilizers and pesticides
Fertilizer: achoose fertilizers according to soil conditions and crop types;
b.Reasonable use of farm manure and chemical fertilizer.
Pesticides: aAccording to the occurrence and development law of pests and diseases, the right medicine is prescribed;
b.Different pesticides are used alternately to improve efficacy and delay or prevent the occurrence of drug resistance;
c.Promote the development and use of biopesticides.
11. Alkali and identification methods of chemical fertilizers.
Color identification: nitrogen fertilizer: generally white.
Phosphate fertilizers: mostly very dark in color, generally gray, dark gray or grayish-black.
Potash: Generally white.
Odor identification: In addition to ammonium bicarbonate, which has the special smell of ammonium in nitrogen fertilizer, other varieties generally have no special odor. Phosphate and potash fertilizers are generally odourless.
Solubility identification.
Take a small sample of the fertilizer ground into powder, place it in a glass test tube, add 10 15 ml of purified water, shake it well, and observe its dissolution. All dissolved are potash fertilizers and nitrogen fertilizers; Insoluble or partially dissolved is phosphate fertilizer.
Alkali grinding. Take a small sample of nitrogen fertilizer and potassium fertilizer, add hydrated lime respectively, mix and grind, and the ammonia gas with pungent odor is released from nitrogen fertilizer, while ammonia gas with no irritating odor is released from potassium fertilizer.
nh4)2so4+ca(oh)2=caso4+2nh3↑+2h2o
2nh4cl+ca(oh)2=cacl2+2nh3↑+2h2o
2nh4no3+ca(oh)2=ca(no3)2+2nh3↑+2h2o
Summary: One look, two smells, three dissolutes, four alkalis.
Differences between different nitrogen fertilizers.