Please list the key points of scientific knowledge and easy mistakes in the three years of junior hi

(1) According to zn + 2h+ = zn2+ +h2, n(zn)=n(h2) can be obtained

There is m(zn)=65*

w（cu）=

2) The above equation can be calculated as n(h+)=

i.e. n(h2so4)=

m（h2so4）=

w（h2so4）=

Solution: According to the parallel circuit, it can be known that the voltage is equal, the current passing through the small resistance is large, which can be obtained from Joule's law, and in the parallel circuit, the resistance is small, and the heat generated in the same time is more, so the answer to this question is: b

It can be obtained from step 1: because it is a colorless solution after adding water, iron sulfate is not present. Because iron sulfate is yellow.

There is also the fact that calcium chloride and potassium carbonate or calcium chloride and potassium sulfate cannot exist at the same time. It will produce calcium carbonate white precipitate. Zinc carbonate is not an intolerable salt, so it certainly does not exist.

It can be obtained from step 2: after adding acid, there is a gas that can make the clarified lime water turbid. So there is potassium carbonate.

With potassium carbonate, calcium chloride is definitely non-existent from the above analysis. From step 3: due to the white precipitate generated by adding silver nitrate, there are chloride ions in the solution, and calcium chloride is excluded, so it can only be sodium chloride.

The above analysis can lead to the answer.

The substances that must not be included are: calcium chloride, iron sulfate, zinc carbonate.

Must contain substances: potassium carbonate, sodium chloride.

The substances that may be contained are: Potassium sulfate understood.

The substance that must not be contained in the original mixture is CaCl2 put in sufficient water, the mixture is completely dissolved, and a colorless transparent solution is obtained The mixture does not have CaCO3

The substances that must be contained in the original mixture are ZnCO3, K2CO3, NaCl judging by (2)(3).

The substances that may be contained in the original mixture are Fe2(SO4)3, K2SO4

Judging from (3) and (2).

The substances that must not be included in the original mixture are: CaCl2 Fe2(SO4)3 ZnCO3

The substance that must be contained in the original mixture is: NaCl K2CO3 The substance that may be contained in the original mixture is: K2SO4

The explanation of the second floor is already very detailed.

1 The mass can be measured with a tray balance Since the mass of a pin is small, so we count 50 pins at a time Measure the mass with a tray balance and divide by 50 to get Repeat the above operation 2 3 times to find the average.

Volume with a graduated cylinder Add a certain amount of water to the vector cylinder to make it read as an integer, and then gently put in a certain amount of pins to make the liquid level in the graduated cylinder rise to a certain height (such as 5ml) and then count the number of pins added The difference in the volume of the liquid level before and after the graduated cylinder is divided by the number of pins You can also repeat the above operation 2 3 times to find the average.

2 Under standard atmospheric pressure, the temperature of the ice-water mixture is 0 and the boiling water is 100 degrees, that is, at the standard atmospheric pressure, the temperature between the ice-water mixture and the boiling water is evenly divided into 100 parts, 1 part is 1, so the 96 of the thermometer corresponds to the standard 100, when its indication is 26, that is, it is higher than the ice-water mixture 24 24 corresponds to the standard 25, that is, the room temperature is higher than the standard 0, the temperature is 25, so the room temperature is 25

1: Weigh the mass m of n pins on a tray balance, then the mass of one pin is m n

Then put n pins into a beaker filled with water, and measure the volume v of the spilled water with a graduated cylinder, then the volume of one pin is v n

2: The actual temperature of the ice-water mixture is 0, and the actual temperature of boiling water under standard atmospheric pressure is 100, so it can be judged that the true value of each degree of this thermometer is (98-2) 100=, so the true temperature of 26 is (26-2)*

1。Take 20 pins, measure the mass of 20 pins with a flat disc (put the object on the left plate, put the weight on the right plate), and divide the total weight of the 20 pins by 20 to equal the mass of each pin. Then take 20ml of water and pour it into a graduated cylinder, and then put 20 pins in it, you can get the volume of 20 pins, divide by 20, which is the volume of each pin.

2。The temperature of the ice-water mixture is 0, and the temperature of the standard atmospheric pressure boiling water is 100, according to which we can know that if 2 of the thermometer is 0, then the 102 of the thermometer is 100, but the thermometer shows 98, and we can know that if the original standard thermometer represents 1, then each compartment of this thermometer represents Celsius, so (26-2) *

1.Draw 100 pins from a box of pins, and weigh the mass m of these 100 pins with a tray balance;

Pour the water in the beaker into the graduated cylinder and measure the volume of water v1 Put 100 pins into the graduated cylinder and measure the total volume of water and pins v2 The volume of 100 pins is vTotal v2 v1

The mass of a pin is m m total 100

The volume is v (v2 v1) 100

2.According to the title, the actual temperature represented by each cell on the thermometer is 100 (98 2) 25 24

The actual temperature of the indoor air.

What's the second lesson, now you've all changed to new textbooks.

The first question is that gravity is straight downward, so it is necessary for Kong Zeling to have a force of equal magnitude in the opposite direction of the other direction, acting on the same straight line to maintain the balance of the two forces, so that it can move in a straight line at a uniform speed.

2.Relative movement, there are many possibilities for the direction of throwing.

3.I'm not sure I'm staring at Huai Ding, I'm helping you take a look.

4.Gravity and friction are not in the same direction and do not produce a relative tendency to motion.

5.The bubbles and the water exert the opposite force.