First, explain the key and difficult knowledge.

Electrolysis of water

Test method and phenomenon summary of electrode gas volume

The volume of positive electrode gas is 65438+ negative electrode 0/2 gas, which can rekindle the wood strip with Mars. The gas produced by the positive electrode is oxygen.

The gas volume of the negative electrode is twice that of the positive electrode. Gas can burn in air, and the gas produced by the negative electrode is hydrogen.

Circulation of water

Five links in the great cycle of land and sea:

A evaporation b water vapor transport c precipitation

D surface runoff e infiltration (underground runoff)

The significance of the sea-land cycle;

A make water, atmosphere, rocks and life on earth closely related;

B. let the ocean continuously supply fresh water to the land, so that water resources can be regenerated. Moisturize the land and nourish life.

(C) the importance of water

Colorless and transparent, boiling point 100℃ (pay attention to conditions).

Odorless freezing point 0℃

Abnormal phenomenon of liquid water under normal circumstances, reverse expansion phenomenon

Second, explain the important and difficult knowledge

1, density measurement

(1) measurement principle: ρ = m/v.

(2) Measurement steps: ① Weigh the mass of the object with a balance; ② Measure the volume of an object with a measuring cylinder or a measuring cup; ③ Calculation

2, the application of density knowledge:

(1) In the density formula, if any two quantities are known, the third quantity can be found.

(2) It can be used to identify the types of substances.

3, increase or decrease the pressure method:

(1) Methods of increasing pressure: A. When the pressure is constant, reduce the stress area; B, stress area unchanged, increase the pressure.

(2) Methods to reduce the pressure: A. When the pressure is constant, increase the stress area; B, when the stress area is constant, reduce the pressure.

4. Characteristics of liquid internal pressure:

(1) There is pressure inside the liquid;

(2) The pressure of liquid increases with the increase of depth;

(3) At the same depth, the pressures in all directions are equal;

(4) The higher the density of different liquids at the same depth, the greater the pressure (the formula for calculating the internal pressure of liquids is p=pgh).

Third, explain the important and difficult knowledge.

1, liquid (gas) will generate upward buoyancy for the object immersed in it.

2. Direction: vertically upward

3. Archimedes principle: buoyancy is equal to the gravity of the liquid displaced by the object.

Formula: F float =G discharge = ρ discharge gv discharge.

Note: (1) buoyancy is only related to the gravity of the liquid displaced by the object;

(2) Buoyancy has nothing to do with the depth, density and shape of the liquid;

(3) For an object completely immersed in liquid, buoyancy is also related to the density of liquid and the volume of the object;

(4) When calculating, the units should be unified (ρ takes kg/m3 and V takes m3).

The ups and downs of an object immersed in a liquid depend on its gravity g and buoyancy f.

①F floating

②F floating >; G floating

(3) F floating =G floating. At this time, v line = V object.

④F floating =G floating. At this time, the fifth row

note:

(1) Floating and sinking are unstable dynamic processes, and floating objects will eventually surface and be in a floating state; The sinking object will eventually sink to the bottom of the liquid and be at rest.

(2) When floating and suspending, the object is in equilibrium due to two forces, and F floating =G (when sinking: F floating +f supporting force =G).

2. Solid objects are immersed in liquid.

(1) when ρ liquid >; ρ thing, floating (final floating)

② When ρ liquid

③ Pause when ρ liquid = ρ substance.

3. Application of floating and sinking conditions

(1) ship

(1) Because when floating, F floats =G, so the buoyancy of the same ship is unchanged from sea to river or from river to sea.

(2) According to F float = ρ row g v, the same ship sailed from the sea to the river. Because F floats unchanged and ρ row decreases, V row will increase, that is, the hull will sink slightly.

(2) Submarine: By draining and filling water into the water tank, it changes its own gravity and makes it float and sink.

(3) Densitometer: Because F float = ρ row g v row, the liquid density is different, the liquid volume discharged by the densimeter is different, and the corresponding position of the liquid surface is also different.

Fourth, explain the important and difficult knowledge.

1, solute: dissolved substances such as sucrose, salt and potassium permanganate are called solutes.

2. Solvent: A substance that can dissolve other substances (such as water and alcohol). Water is a good solvent and many substances can be dissolved in it.

3. Solution: A substance obtained by dissolving a solute in a solvent (iodine, potassium permanganate solution, sugar water, salt water).

(2) Suspension, emulsion and mixture

1. suspension: a substance formed by small solid particles suspended in a liquid.

Some potions, such as "barium meal", need to be shaken well when taking, and the liquid will become turbid and opaque, that is, suspension.

2. Emulsion: a substance formed by dispersing small droplets in an (immiscible) liquid.

Milk, milky white and opaque, will appear a layer of white grease when left for a long time. This is emulsion.

3. Mixture: A substance composed of many substances. There are many substances like sugar water in life. They have many ingredients mixed together and are a mixture. Solutions, suspensions and emulsions are all mixtures.

Substance suspension emulsion

Whether it is transparent or opaque, turbid or transparent.

Whether it is stratified for a long time, stratified for a long time, and not stratified for a long time.

Non-uniformity, instability, uniformity and stability

mix

(3) Common solvents

Water can dissolve many substances and is the most commonly used and better solvent. Commonly used solvents are alcohol, gasoline, acetone, etc.

(1) solution has the characteristics of uniformity and stability (it will not delaminate even if it is left for a period of time). The essential difference between solution, suspension and emulsion is that the particle size is different in water.

(2) salad oil forms a solution in gasoline. It shows that the solubility of the same substance in different solvents is different.

Key points:

Under certain conditions (a certain amount of solvent, a certain amount of water), solute can not be dissolved in solvent indefinitely.

Saturated solution and unsaturated solution

1. saturated solution: A solution in which a solute cannot be dissolved in a certain amount of solvent at a certain temperature is called a saturated solution of this solute.

2. Unsaturated solution: A solution that can continue to dissolve a solute in a certain amount of solvent at a certain temperature is called an unsaturated solution of this solute. The solution before continuous addition of copper sulfate is an unsaturated solution of copper sulfate.

Can an unsaturated solution be converted into a saturated solution? -increase solute, evaporate solvent and reduce temperature (general)

Saturated solution can also be converted into unsaturated solution, solvent water can be added, and the temperature can be raised (generally).

3. concentrated solution and dilute solution: the solution with more solute in the solution is called concentrated solution; Some solutes are less, which is called dilute solution.

(2) solubility

1, solubility is used to indicate the solubility of a substance, that is, the mass of a substance saturated in100g solvent at a certain temperature is the solubility of the substance in the solvent.

note:

(1) To understand this concept, grasp four words: a certain temperature,100g of solvent (usually water), saturation, and the mass of solute (in grams).

(2) The greater the solubility value, the stronger the solubility of the substance at this temperature.

Calculation of solubility: If the solubility is R, the amount of saturated solution is A, the amount of solvent is B, and the solubility is C (all in grams), the three types are:

(l) it is known that b and c find R.

(2) it is known that r and a find b or c.

(3) it is known that r and c find b.

The solubility at 20℃ is greater than10g1-10g0.01-kloc-0/g is less than 0.01g.

The solubility grade is soluble, soluble, slightly soluble and insoluble.

Solubility grade of substance:

Description:

Soluble, soluble, slightly soluble and insoluble are all relative. There is nothing absolutely insoluble in nature. Substances that are customarily called "insoluble" have little solubility and are usually ignored.

The factors that affect the solubility of solids are: the properties of solute and solvent (internal factors)

Temperature (external cause)

(3) Solubility curve: With temperature as the abscissa and solubility as the ordinate, we can intuitively see the change of solubility of substances with temperature.

(1) Different solubility values of the same substance at different temperatures;

(2) Solubility values of different substances at the same temperature;

(3) The degree to which the solubility of a substance is affected by temperature changes;

(4) Compare the solubility of various substances at a certain temperature.

Description:

The solubility of different substances is affected by temperature differently.

(1) The solubility of most substances increases with the increase of temperature. ① Great influence, such as ammonium nitrate, potassium nitrate, sodium nitrate, etc. , showing a steep curve.

(2) It has little influence, such as sodium chloride, potassium chloride and ammonium chloride, showing a gentle curve.

(2) The solubility of a few substances decreases with the increase of temperature, such as the meaning of each point on the solubility curve of calcium hydroxide.

In the "Potassium Nitrate Solubility Curve", what does the point with abscissa 60 and ordinate 1 10 mean? (1) means that the solubility of potassium nitrate in water at 60℃ is 1 10g, (2) means that it can be dissolved in water at 60℃ when it reaches saturation 1 10g.

(4) mass fraction of solute

1, and the mass fraction of solute is a quantitative expression of solution composition. That is, the amount of solute contained in a certain amount of solution.

Formula: mass fraction of solute in solution = mass of solute/mass of solution.

= solute mass/(solute mass+solvent mass)

(usually expressed in decimal or percentage)

The relationship between solute, solute, solvent and solution mass fraction;

The mass of solute is constant, increasing and decreasing.

The quality of solvent decreases and increases constantly.

The quality of solution drops, rises, rises and falls.

The mass fraction of solute becomes larger, smaller, larger and smaller.

There are four types of (1) calculations:

(1) Know the solvent mass of solute and get the mass fraction of solute.

(2) Calculate the mass of solute and solvent needed to prepare a solution with a certain mass fraction of solute.

③ Calculation of solubility and solute mass fraction in saturated solution at this temperature.

④ Calculation of solution dilution or concentration.

(2) The solution is usually calculated by measuring the volume with a measuring cylinder. Attention should be paid to the conversion between the volume and quality of the solution, that is, the application of density.

(3) For the calculation of solution dilution or evaporation concentration, it is necessary to keep the mass of solute unchanged before and after solution dilution or evaporation concentration, that is, the mass of concentrated solution × the mass fraction of solute in concentrated solution = the mass of dilute solution × the mass fraction of solute in dilute solution.

4) Method of expressing solution composition by volume fraction:

2, preparing a solution with a certain solute mass fraction:

① Calculation (mass or volume of solvent and solute)

② Weighing (weighing or measuring)

③ Dissolve (bottles and labels).

I don't have any practice. Here you are. I hope it works. Our teacher gave it to us. There are still two weeks after the end of the semester. Call me if you like.