The complete solution of chemistry and other reference books are written to look at the lowest part

The cause of the uneven liquid level is the problem of capillary phenomenon.

The adhesion of water in the capillary is stronger than the surface tension, and it is understood in a nutshell that water can stick to the pipe wall, allowing it to appear in a concave liquid with a higher liquid level near the pipe wall. The convex liquid level can only appear when the graduated cylinder is filled with water, which can be understood as that there is no pipe wall on the top to stick, so it can only be raised. But don't forget, the scale in the graduated cylinder will not reach the top, so the operation of the convex liquid level is not standardized.

You can take a look at the Wikipedia entry for "capillary phenomena" to deepen your understanding. However, if you only want the reason why there is no convex liquid level, "the convex liquid level can only appear when the graduated cylinder is filled with water, and the scale in the graduated cylinder will not reach the top, so the operation of the convex liquid level is not standardized." That's enough.

Supplement - Mercury is difficult to access in the middle or high school range, so it is generally not mentioned, and it is generally looked at the highest place. But I still have to say that there are many wrong theories in the textbooks, such as nitrates are soluble, exceptions such as potassium perchlorate, and sodium antimonate also overturns that sodium salts are soluble. Don't be superstitious that textbooks are very helpful for practical life and experiments.

？？Under what circumstances will there be a convex liquid level, and the liquid level will not be higher than the edge of the graduated cylinder in the graduated cylinder, how can there be a convex liquid level!

What solution can form a convex liquid surface?

When measuring the liquid with a graduated cylinder, the graduated cylinder should be flattened, and the line of sight should be level with the lowest part of the concave liquid level when reading; If you look up at the liquid level, the reading is lower than the actual level, if you look down at the liquid level, the reading is larger than the actual level The student's initial gaze is at the lowest point of the concave liquid level in the graduated cylinder, the reading is 20ml, and the actual volume is equal to 20ml; After pouring out part of the liquid, look up at the lowest part of the concave liquid level, the reading will be smaller than the actual one, then the actual volume should be greater than 10ml, then the actual volume of the liquid poured by the student is less than 10ml

Therefore, a

Answer] B Answer Analysis] The first line of sight is kept at the lowest point of the concave liquid surface of the liquid in the graduated cylinder, and reading for 15ml is the correct way to measure the liquid, such as clapping out part of the liquid, looking down at the lowest part of the concave liquid level, reading for 9 °lm, the reading is large, but the actual volume of the liquid measured is just too small, and the remaining volume is less than 9 °ml, so the volume of the actual liquid poured out by the student is definitely greater than 6ml. Therefore, choose B

This is determined by the surface tension of the liquid, the higher the density, the greater the surface tension, and the convex liquid surface will be formed; Otherwise, a concave liquid surface will be formed.

Those with a density smaller than or equal to water will form a concave liquid surface (such as alcohol), while those with a greater density than water will become a convex liquid surface, or because of the intermolecular force between water and glass, the tensile force between water and glass is less than the tensile force between water and glass. So at the junction of water and glass, the water will be pulled up by the glass and will be concave.

If it is mercury, the liquid level is convex, and it depends on the convex liquid level. The force between mercury is greater than that between mercury and glass.

The line of sight should be level with the lowest part of the concave liquid level to make the measurement more accurate.

This is caused by the surface tension of the liquid.

Decidingly, the higher the density, the greater the surface tension, and the convex liquid surface will be formed; Otherwise, a concave liquid surface will be formed.

Those with a density smaller than or equal to water will form a concave liquid surface (such as alcohol), while those with a greater density than water will become a convex liquid surface lift.

Or rather: because of the intermolecular forces between water and glass.

The tensile force between the water is smaller than the tensile force between the water and the glass. So at the junction of water and glass, the water will be pulled up by the glass and will be concave.

If it's noisy, it's mercury.

If the liquid level is convex, it depends on the convex liquid level. The force between mercury is the force between mercury and glass.

The graduated cylinder can resemble a capillary system with respect to a large-area container, depending on the surface tension p=2 r

is the surface tension, r is the capillary radius) to form an additional pressure, the water will form a concave surface, and the mercury will form a convex liquid surface.

This is determined by the surface tension of the liquid, the greater the density, the greater the surface tension, and the early will form a convex liquid surface; Otherwise, a concave liquid surface will be formed.

Those with a density smaller than or equal to water will form a concave liquid surface (such as alcohol), while those with a greater density than water will have a convex liquid surface.

In other words, because of the intermolecular force between water and glass, the tensile force between water and glass is smaller than the tensile force between water and glass. So at the junction of water and glass, the water will be pulled up by the glass and will be concave.

If it is mercury, the liquid level is convex, it depends on the convex liquid bond respect. The force between mercury is greater than that between mercury and glass.

The line of sight should be level with the lowest part of the concave liquid level to make the measurement more accurate.

Do not look up or down when reading, and keep the line of sight level with the lowest part of the concave liquid level; Looking up is from the bottom to the top so the reading is small, and when looking down, the ridge is looking down from the top to the bottom, so the reading is too large

Therefore, the answer is: the lowest permeability of the concave liquid level; on the small side; On the large side

Use a graduated cylinder. When measuring the liquid, the graduated cylinder should be flat, and the line of sight should be kept level with the lowest part of the concave liquid level when reading; If you look up at the liquid level, the reading is lower than the actual outrage, and if you look down at the liquid level, the reading is larger than the actual one

If a student looks down at the lowest part of the liquid concave in the graduated cylinder when measuring the liquid, the reading will be larger than the actual balance, then the actual volume should be less than 15ml

Therefore, the answer is: keep the lowest part of the concave liquid level level; ＜．