Basic concepts:
1. Chemical change: changes that produce other substances.
2. Physical changes: other substances have not changed.
3. Physical properties: properties that can be displayed without chemical changes.
(such as color, state, density, smell, melting point, boiling point, hardness, water solubility, etc.). )
4. Chemical properties: the properties of substances in chemical changes.
(such as flammability, combustion-supporting, oxidizing, reducing, acidity and alkalinity, stability, etc.). )
5. Purity: It consists of a substance.
6. Mixture: It consists of two or more pure substances, each of which maintains its original properties.
7. Element: A general term for a class of atoms with the same nuclear charge number (i.e. proton number).
8. Atom: the smallest particle in chemical change, which can't be subdivided.
9. Molecule: the smallest particle that keeps the chemical properties of a substance and can be subdivided in chemical changes.
10, simple substance: a pure substance composed of the same element.
1 1, compound: a pure substance composed of different elements.
12. oxide: a compound composed of two elements, one of which is oxygen.
13, chemical formula: a formula for expressing the composition of matter with element symbols.
14. Relative atomic mass: the value obtained by comparing the mass of a carbon atom with112.
Relative atomic mass of atoms =
Relative atomic mass ≈ proton number+neutron number (because atomic mass is mainly concentrated in the nucleus)
15, relative molecular mass: the sum of the relative atomic masses of each atom in the chemical formula.
16, ion: charged atom or atomic group.
17, the structure of the atom:
The relationship between atoms and ions:
Note: In ions, the number of nuclear charges = the number of protons ≠ the number of extranuclear electrons.
18, four basic types of chemical reactions:
(1) Combination reaction: A reaction in which two or more substances form one substance.
Such as: A+B = AB
② Decomposition reaction: a reaction in which one substance generates two or more other substances.
For example: AB = A+B
③ Displacement reaction: a reaction between a simple substance and a compound to produce another simple substance and another compound.
Such as: a+BC = AC+B.
(4) Double decomposition reaction: a reaction in which two compounds exchange components with each other to form two other compounds.
For example: AB+CD = AD+CB.
19. Reduction reaction: the reaction in which the oxygen of oxygen-containing compounds is taken away (not the basic reaction type of chemistry).
Oxidation reaction: a chemical reaction between a substance and oxygen (not the basic reaction type of chemistry)
Slow oxidation: the oxidation reaction is very slow and even difficult to detect.
Spontaneous combustion: spontaneous combustion caused by slow oxidation
20. Catalyst: A substance that can change the chemical reaction rate of other substances in the process of chemical change, but its quality and chemical properties have not changed before and after the chemical change (Note: 2h2o 2 = = 2h2o+O2 = MnO2 is the catalyst for this reaction).
2 1, law of conservation of mass: the total mass of substances participating in chemical reactions is equal to the total mass of substances generated after the reaction.
Before and after the reaction, the number, species and quality of atoms remain unchanged; Elements are of the same type)
22. Solution: One or more substances are dispersed into another substance to form a uniform and stable mixture.
Composition of solution: solvent and solute. (Solute can be solid, liquid or gas; When solids and gases are dissolved in liquids, they are solutes and liquids are solvents. When two liquids are mutually soluble, the solvent is one with more quantity and the solute is one with less quantity; When there is water in the solution, no matter how much water there is, we are used to using water as a solvent and others as solutes. )
23. Solid solubility: The mass of a solid substance dissolved in100g solvent at a certain temperature is called the solubility of this substance in this solvent.
24. Acid: A compound in which all cations produced during ionization are hydrogen ions.
For example: HCl==H++Cl-
Nitric acid ==H++nitric acid-
H2SO4==2H+ + SO42-
Alkali: A compound in which all anions produced during ionization are hydroxyl ions.
For example: KOH==K++OH-
NaOH==Na+ + OH -
Ba(OH)2==Ba2+ + 2OH -
Salt: a compound that produces metal ions and acid ions when ionized.
For example, KNO3==K++NO3-
Na2SO4==2Na+ + SO42-
BaCl2==Ba2+ + 2Cl -
25. Acid oxide (nonmetallic oxide): Any oxide that can react with alkali to form salt and water.
Basic oxide (metal oxide): Any oxide that can react with acid to form salt and water.
26. Crystal hydrate: substances containing crystal water (such as Na2CO3. 10H2O, CuSO4). 5H2O)。
27. deliquescence: the phenomenon that substances can absorb moisture in the air and become damp.
Weathering: crystal hydrate is placed in dry air at normal temperature,
The phenomenon that crystal water can be gradually lost and turned into powder.
28. Combustion: The violent oxidation reaction between combustible substances and oxygen releases light and heat.
Combustion conditions: ① combustible; ② Oxygen (or air); (3) The temperature of combustible materials should reach the ignition point.
Basic knowledge and theory:
1. Composition of air: 78% nitrogen, 2 1% oxygen and 0.94% rare gas.
Carbon dioxide accounts for 0.03%, and other gases and impurities account for 0.03%.
2. Main air pollutants: NO2, CO, SO2, H2S, NO and other substances.
3. Chemical formulas of other common gases: NH3 (ammonia), CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane),
SO2 (sulfur dioxide), SO3 (sulfur trioxide), NO (nitric oxide),
NO2 (nitrogen dioxide), H2S (hydrogen sulfide), HCl (hydrogen chloride)
4. Common acids or ions: SO42- (sulfate), NO3- (nitrate), CO32- (carbonate), ClO3- (chloric acid),
MnO4- (permanganate), MnO42- (manganate), PO43- (phosphate), Cl- (chloride),
HCO3- (bicarbonate), HSO4- (bisulfate), HPO42- (phosphate),
H2PO4- (dihydrogen phosphate), OH- (hydroxyl), HS- (hydrosulfide), S2- (sulfur ion),
NH4+ (ammonium radical or ammonium ion), K+ (potassium ion), Ca2+ (calcium ion), Na+ (sodium ion),
Mg2+ (magnesium ion), Al3+ (aluminum ion), Zn2+ (zinc ion), Fe2+ (ferrous ion),
Fe3+ (iron ion), Cu2+ (copper ion), Ag+ (silver ion) and Ba2+ (barium ion).
The valence of each element or atomic group corresponds to the charge number of the above ions: textbook P80.
Monovalent potassium, sodium, hydrogen and silver, divalent calcium, magnesium, barium and zinc;
One, two, copper, mercury, iron, trivalent aluminum and tetravalent silicon. (oxygen -2, chlorine in chloride is-1, fluorine is-1, and bromine is-1).
(In simple substance, the valence of elements is 0; In the compound, the algebraic sum of the valence of each element is 0)
5, chemical formula and valence:
(1) The meaning of the chemical formula: ① Macro meaning: a. stands for a substance;
B, indicate the elemental composition of the substance;
② Microscopic significance: a. Molecules representing matter;
B, indicating the molecular composition of the substance;
③ Meaning of quantity: a. Represents the number ratio of atoms in a substance molecule;
B. indicates the mass ratio of the elements that make up the substance.
(2) Reading and writing simple chemical formulas
(1) is directly represented by element symbols: a. Simple metal. Such as: potassium, potassium, copper, copper, silver, silver and so on. ;
B. solid nonmetal. Such as carbon, carbon, sulfur, sulfur, phosphorus and phosphorus.
C. rare gases. Such as: helium (gas) helium neon (gas) neon argon (gas) argon, etc.
(2) Simple substance of polyatomic molecule: If the molecule is composed of several atoms of the same kind, write a few in the lower right corner of the element symbol.
For example, each oxygen molecule consists of two oxygen atoms, so the chemical formula of oxygen is O2.
Chemical formula of diatomic molecule: O2 (oxygen), N2 (nitrogen), H2 (hydrogen).
F2 (fluorine gas), Cl2 (chlorine gas), Br2 (liquid bromine)
Simple chemical formula of polyatomic molecules: ozone O3, etc.
(3) Reading and writing of chemical formula of compound: read before writing, read before writing.
① A compound composed of two elements: pronounced as "a chemical substance", such as MgO (magnesium oxide) and NaCl (sodium chloride).
② Compounds composed of acid radicals and metal elements: pronounced as "an acid", such as KMnO4 (potassium permanganate) and K2MnO4 (potassium permanganate).
Magnesium sulfate, calcium carbonate
(4) Judging the valence of elements according to the chemical formula, and writing the chemical formula of the compound according to the valence of elements:
① The basis for judging the valence of elements is that the algebraic sum of positive and negative valence in the compound is zero.
(2) Write the chemical formula according to the valence of elements:
A, writing element symbols according to the positive, negative and right valence of elements and marking the valence;
B. See if the valence of an element is a divisor and turn it into the simplest ratio;
C. Cross-switch, and write the valence that has been reduced to the simplest ratio in the lower right corner of the element symbol.
6. Teaching material P73. Remember these 27 elements, symbols and names.
Extranuclear electron configuration: element 1-20 (remember the name of the element and the schematic diagram of the atomic structure).
Arrangement rules: ① Each layer can arrange 2n2 electrons at most (n means the number of layers).
② The number of electrons in the outermost layer shall not exceed 8 (the outermost layer shall not exceed 2 in the first layer).
③ Fill in the inner layer first and then the outer layer.
Note: The chemical properties of elements depend on the number of electrons in the outermost layer.
The outermost electron number of metal element atoms
The outermost electron number of nonmetallic elements is ≥ 4, which is easy to obtain electrons and has active chemical properties.
There are 8 electrons in the outermost layer of rare gas element atoms (there are 2 electrons in he), and the structure and properties are stable.
7. Principles of writing chemical equations: ① Based on objective facts; ② Follow the law of conservation of mass.
Steps of writing chemical equations: writing, matching, remembering, etc.
8. Expression of pH value -pH value
Description: (1)PH =7, and the solution is neutral; When the PH value is less than 7, the solution is acidic; PH value > 7. The solution is alkaline.
(2) 2) The closer the pH value is to 0, the stronger the acidity is; The closer the PH value is to 14, the stronger the alkalinity is. The closer the PH value is to 7, the weaker the acidity and alkalinity of the solution is, and the closer it is to neutrality.
9, metal activity sequence table:
(Potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin, lead, hydrogen, copper, mercury, silver, platinum, gold)
Description: (1) The metal on the left is more active, and the metal on the left can be replaced from the salt solution of the metal on the right.
(2) The metal to the left of hydrogen can replace the hydrogen in acid; The one to the right of hydrogen can't.
(3) Potassium, calcium and sodium are relatively active, and they directly react with water in the solution to displace hydrogen.
10, material structure:
1 1, meaning and writing of chemical symbols:
The meaning of (1) chemical symbol: a. Element symbol: ① indicates an element; ② Represents an atom of an element.
B. chemical formula: point 5 and point (1) of this knowledge point.
C ion symbol: indicates the number of charges carried by ions and ions.
D. Valence symbol: indicates the valence of an element or an atomic group.
When there is a number in front of the symbol (valence symbol has no number), the meaning of the constituent symbol only indicates the number of particles.
(2) Writing of chemical symbols: a. Representation of atoms: represented by elemental symbols.
B. Expression of molecules: chemical formula.
C. Representation of ions: use ion symbols.
D. Expression method of valence: expressed by valence symbol.
Note: When the number of atoms, molecules and ions is greater than "1", it can only be added before the symbol, but not elsewhere.
12, the relationship between atoms, molecules, ions, elements and substances (pure substances and mixtures):
13、
14, commonly used gas generating devices and gas gathering devices:
generating equipment
gathering unit
[Solid (+solid)]
[solid+liquid]
Simple device [solid+liquid] upward drainage method
Downward exhaust method
Air emission method
15, laboratory preparation methods of three gases and their differences;
Gaseous oxygen (O2), hydrogen (H2) and carbon dioxide (CO2).
Medicine potassium permanganate (KMnO4) or hydrogen peroxide (H2O2) and manganese dioxide (MnO2).
[solid (+solid)] or [solid+liquid] zinc particles (Zn) and hydrochloric acid (HCl) or dilute sulfuric acid (H2SO4)
[solid+liquid] limestone (marble) (CaCO3) and dilute hydrochloric acid (HCl)
[solid+liquid]
Reaction principle 2KMnO4 == K2MnO4+MnO2
+O2↑
Or 2h2o2 = = 2h2o+O2 = Zn+H2SO4 = ZnSO4+H2 =
Zn+2HCl=ZnCl2+H2↑
Calcium carbonate+hydrochloric acid = calcium chloride +H2O+ carbon dioxide
Instrument P36 Figure 2- 17 (for example, A of 14)
Or P 1 1 1. Figure 6-10 (b or c of14) p11. Figure 6- 10.
(e.g. b or c of 14) p11. Figure 6- 10
(e.g. b or c of 14)
During the inspection, stick to using Mars to probe into the gas cylinder. If the stick is rekindled, it is oxygen; Otherwise, it is not oxygen that ignites the batten and extends into the bottle. The flame on the batten goes out and the flame at the bottle mouth is light blue. Then the gas is hydrogen, and clear lime water is introduced to see if it becomes turbid. If it is turbid, it is CO2.
Collection method ① Drainage method (insoluble in water) ② Upward exhaust of bottle mouth (density greater than air) ① Drainage method (insoluble in water) ② Downward exhaust of bottle mouth (density less than air) ① Upward exhaust of bottle mouth.
(denser than air)
(cannot be collected by drainage method)
Check integrity
(Purification) Use a wooden stick with a spark and lay it flat on the bottle mouth. The stick is rekindled and the oxygen is full, otherwise it will be dissatisfied.
If "poof", hydrogen is pure; If there is a sharp popping sound, it means that the hydrogen is impure. Put a burning wooden stick flat on the mouth of the gas container. If the flame goes out, it is full; Or it's not full.
Forward, backward, forward.
Precautions ① Check the air tightness of the equipment.
(When preparing the first drug, you should pay attention to the following matters)
(2) The mouth of the test tube should be slightly inclined downward (to prevent the small water droplets condensed at the mouth of the test tube from flowing back to the bottom of the test tube and breaking the test tube).
(3) When heating, the test tube should be heated evenly first, and then heated in the drug part.
(4) After collecting oxygen by drainage method, first withdraw the catheter and alcohol lamp (to prevent the water in the washbasin from flowing backwards and breaking the test tube) (1) to check the air tightness of the device.
(2) The nozzle of the long-necked funnel should be inserted under the liquid surface;
(3) Before igniting hydrogen, be sure to check the purity of hydrogen (in air, the volume of hydrogen reaches 4%-74.2% of the total volume, and it will explode when ignited. (1) Check the air tightness of the device.
(2) The nozzle of the long-necked funnel should be inserted under the liquid surface;
(3) It cannot be collected by drainage.
16, properties of some important common gases (physical and chemical properties)
Physical properties of matter
Chemical use (usually)
oxygen
(O2) Colorless and odorless gas, insoluble in water and slightly higher in density than air.
(1) ①C+O2==CO2 (emitting white light and releasing heat)
1, used for breathing
Step 2 make steel
3. Gas welding
(Note: O2 has combustion-supporting function, but it is not flammable and can't burn. )
②S+O2 ==SO2 (light blue flame in the air)
Flame; Violet-blue flame in oxygen)
③4P+5O2 == 2P2O5 (producing white smoke and white solid P2O5)
④3Fe+2O2 == Fe3O4 (burning violently, sparks everywhere, releasing a lot of heat and producing black solids).
⑤ Candles burn in oxygen, giving off white light and heat.
hydrogen (H)
(H2) Colorless and odorless gas, almost insoluble in water, less dense than air, is the lightest gas. ① Flammability:
2H2 + O2 ==== 2H2O
H2+Cl2 = = = 2HCl1+0, gas-filled, spacecraft (less dense than air).
2. Synthetic ammonia and hydrochloric acid
3. Gas welding and gas cutting (flammability) 4. Refined metal (reducing)
② Reducibility:
H2 + CuO === Cu + H2O
3H2 + WO3 === W + 3H2O
3H2 + Fe2O3 == 2Fe + 3H2O
Carbon dioxide (CO2) is a colorless and odorless gas, which is denser than air and soluble in water. Solid carbon dioxide is called "dry ice". CO2+H2O ==H2CO3 (acidic)
(H2CO3 === H2O+CO2↑ = =) (unstable)
1, used for fire extinguishing (using its incombustibility, not supporting combustion)
2. Beverage, fertilizer and soda ash
CO2+Ca(OH)2 ==CaCO3↓+H2O (identify CO2)
CO2 +2NaOH==Na2CO3 + H2O
Oxidation: CO2+C == 2CO
CaCO3 == CaO+CO2↑ = (industrial CO2)
Carbon monoxide is colorless, odorless, slightly less dense than air and almost insoluble in water. Toxic gas ① Flammability: 2CO+O2 == 2CO2.
(The flame is blue and gives off a lot of heat, so it can be used as gas fuel) 1, as fuel.
2. Melting metal
② Reducibility:
CO + CuO === Cu + CO2
3CO + WO3 === W + 3CO2
3CO + Fe2O3 == 2Fe + 3CO2
(Combined with hemoglobin in blood, destroying the ability of blood to transport oxygen)
Problem solving skills and instructions:
1. Reasoning problem-solving skills: look at its color, its state, its change, the first generation test.
Color of common substances: most gases are colorless, most solid compounds are white, and most solutions are colorless.
2, the color of some special substances:
Black: manganese dioxide, copper oxide, ferroferric oxide, carbon and ferrous sulfide.
Blue: CuSO4? 5H2O, Cu(OH)2, CuCO3, Cu2+-containing solution,
Liquid solid O2 (light blue)
Red: copper (bright red), iron oxide (reddish brown) and red phosphorus (deep red)
Yellow: solution containing sulfur (elemental sulfur) and Fe3+ (brownish yellow).
Green: FeSO4? 7H2O, solution containing Fe2+ (light green), basic copper carbonate [Cu2(OH)2CO3]
Colorless gases: N2, carbon dioxide, carbon monoxide, oxygen, H2, methane.
Colored gases: Cl2 (yellow-green) and NO2 (red-brown)
Gases with pungent odor: NH3 (this gas can turn wet pH test paper blue) and SO2.
Smell of rotten eggs: H2S
3, some common changes in judgment:
① White precipitated substances insoluble in dilute nitric acid or acid are: BaSO4 and AgCl (just these two substances).
② Blue precipitate: Cu(OH)2 and CuCO3.
③ reddish brown precipitate: Fe(OH)3.
Fe(OH)2 is a white flocculent precipitate, but it quickly turns into a gray-green precipitate in the air and then into a reddish-brown precipitate of Fe(OH)3.
④ The precipitate can be dissolved in acid and release gas (CO2): insoluble carbonate.
⑤ precipitate soluble in acid but not releasing gas: insoluble alkali.
4, the relationship between acid and the corresponding acid oxide:
(1) Acid oxides and acids can react with alkali to form salt and water;
CO2+2 NaOH = = na2co 3+H2O(h2co 3+2 NaOH = = na2co 3+2H2O)
SO2 + 2KOH == K2SO3 + H2O
H2SO3 + 2KOH == K2SO3 + 2H2O
SO3 + 2NaOH == Na2SO4 + H2O
H2SO4 + 2NaOH == Na2SO4 + 2H2O
② Acid oxides react with water to generate corresponding acids: (valence of each element remains unchanged)
CO2+H2O = = h2co 3 SO2+H2O = = h2so 3
SO3+H2O == N2O5 sulfate+H2O = = nitric acid
It shows that these acidic oxide gases can make wet pH test paper turn red.
5. Contact between alkali and corresponding basic oxides:
(1) Both basic oxides and bases can react with acids to form salts and water;
CuO + 2HCl == CuCl2 + H2O
Copper hydroxide+dihydrochloride = = copper chloride+dihydrate
Calcium oxide+hydrochloric acid = = calcium chloride+H2O
Calcium hydroxide+dihydrochloride = = calcium chloride+dihydrate
② Alkali metal oxides react with water to generate corresponding alkali: (The generated alkali must be dissolved in water, otherwise this reaction cannot occur)
K2O + H2O == 2KOH Na2O +H2O == 2NaOH
Bao+H2O == barium hydroxide+calcium oxide = = calcium hydroxide
③ Insoluble alkali will decompose corresponding oxides and water when heated;
Magnesium hydroxide = = magnesium oxide+H2O copper hydroxide = = copper oxide+H2O
2Fe(OH)3 = = fe2o 3+3H2O 2Al(OH)3 = = al2o 3+3H2O
Second, solve the experimental problems: see clearly what the requirements are, what to do and what the purpose is.
(a), the gas used in the experiment is relatively pure, the specific method to remove common impurities:
① In addition to water vapor, concentrated acid, CaCl2 _ 2 solid, soda lime and anhydrous CuSO4 _ 4 can be used (and can be used to test impurities.
Whether there is water vapor in the quality, the color changes from white to blue), quicklime, etc.
② CO2 removal is available: clarified limewater (which can detect whether there is CO2 in impurities), NaOH solution,
KOH solution, alkali lime, etc.
(3) In addition to HCl gas, AgNO3 solution (which can be used to detect whether there is HCl in impurities), limewater,
Sodium hydroxide solution, potassium hydroxide solution
Principle of removing gas impurities: A substance absorbs or reacts with impurities, but cannot absorb or react with effective components, nor can it generate new impurities.
(2), experimental matters needing attention:
① Explosion-proof: Before igniting combustible gas (such as H2, carbon monoxide and methane) or reducing copper oxide and ferric oxide with carbon monoxide and H2, check the gas purity.
② Explosion-proof boiling: When diluting concentrated sulfuric acid, pour concentrated sulfuric acid into water instead of pouring water into concentrated sulfuric acid.
(3) Poisoning prevention: When conducting experiments on the properties of toxic gases (such as CO, SO2 and NO2), it is necessary to prevent poisoning.
In a ventilated kitchen; And pay attention to the treatment of tail gas: CO is ignited and burned;
SO2 and NO2 are absorbed by alkaline solution.
④ backflow prevention: gas is prepared by heating method and collected by drainage method. Pay attention to the order of turning off the lights.
(3), the handling of common accidents:
(1) acid flows to the table and is washed with NaHCO3; Alkali flows to the table and is washed with dilute acetic acid.
(2) On the skin or clothes:
Firstly, washing acid with water, and then washing with 3-5% sodium bicarbonate;
Ii, washing alkali with water, and then coating boric acid;
Ⅲ. Clean the concentrated sulfuric acid with a rag, and then do the first step.
(4) Common impurities that need to be removed in the three gases prepared in the laboratory:
1. Impurity to be removed in oxygen production: water vapor (H2O)
2. Impurities to be removed when preparing H2 with hydrochloric acid and zinc particles: water vapor (H2O), hydrogen chloride gas (HCl, acid mist of hydrochloric acid) (such impurities cannot be removed with dilute sulfuric acid).
3. Impurities to be removed in the production of carbon dioxide: water vapor (H2O) and hydrogen chloride gas (HCl).
Reagents for removing water vapor: concentrated acid, CaCl2 _ 2 solid, alkali lime (mainly composed of NaOH and CaO), quicklime, anhydrous CuSO4 (and check whether there is water vapor in impurities, and the color changes from white to blue), etc.
Reagents for removing HCl gas: AgNO3 solution (which can detect whether there is HCl in impurities), clarified limewater, NaOH solution (or solid) and KOH solution (or solid).
[Quicklime and alkaline lime can also react with HCl gas]
(5) Experimental methods are often used to verify that the mixed gas contains a certain gas.
Verification method of 1.CO: (firstly, verify whether there is CO2 in the mixed gas, and remove it if there is)
The mixed gas is introduced into hot CuO, and then the mixed gas after hot CuO is introduced into clarified limewater. Phenomenon: Black CuO turns red, and clarified limewater becomes turbid.
2. Verification method for the existence of 2.H2: (first verify whether there is water in the mixed gas, and remove it if there is water)
Introducing hot CuO into the mixed gas, and then introducing anhydrous CuSO4 into the mixed gas after hot CuO. Phenomenon: black CuO turns red and anhydrous CuSO4 turns blue.
3. Verification method of 3.CO2: Introduce the mixed gas into the clarified limewater. Phenomenon: Clear limewater becomes turbid.
(6) Design the experiment by yourself
1. Try to design an experiment to prove that candles contain hydrocarbons.
Experimental steps, conclusions of experimental phenomena
(1) Light the candle, cover a dry and clean beaker above the flame, and small water droplets are generated on the inner wall of the beaker, which proves that the candle contains hydrogen.
(2) Cover the beaker dipped in clarified limewater above the candle flame, and the clarified limewater becomes turbid, which proves that the candle contains carbon.
2. Try to design an experiment to prove that CO2 does not support combustion, and its density is higher than that of air.
Experimental Steps Experimental Phenomenon Conclusion Diagram
Put two candles on a shelf with steps, put this shelf in a beaker (as shown in the figure), light the candles, and then pour CO2 along the wall of the beaker. The candles at the bottom of the steps are put out first, and the candles at the top are put out later. It has been proved that CO2 does not support combustion, and its density is higher than air.
Third, solve the calculation problem:
The types of calculation problems are: ① Calculation of mass fraction (elements and solutes).
② Calculated according to chemical equation.
③ Mixed ① and ② calculation.
Calculation of solute mass fraction in (1) solution
Solute mass fraction = ╳ 100%
(2) Calculate the mass fraction of elements in the compound (pure substance)
Mass fraction of an element = ╳ 100%
(3) calculating the mass fraction of the compound in the mixture
Mass fraction of compound = ╳ 100%
(4) calculating the mass fraction of one element in the mixture.
Mass fraction of an element = ╳ 100%
Or: the mass fraction of an element = the mass fraction of the compound/the mass fraction of the element in the compound.
(5) Ability to solve problems
1, Exam: Look at the requirements of the topic, what you know and what you want, and write the chemical equation first if you have one. Find out the relevant formula to solve this problem.
2, according to the chemical equation calculation steps:
① Set an unknown quantity.
② Write the correct chemical equation.
③ Write down the relative molecular mass, known quantity and unknown quantity of related substances.
④ List the proportional formula and solve it.
5 answer.