Can water in a test tube boil in boiling water?

This kind of topic should be junior high school, right?

The so-called standard answer for junior high school is:

The water in the test tube in the boiling water bath can reach the boiling point, but does not boil, the explanation is that it cannot continue to absorb heat when it reaches the boiling point, so it does not boil.

The ways to make it boil are:

1. Cover the container where the boiling water outside the test tube is located. Because the pressure increases after sealing, the boiling point increases, and the water temperature increases, the water in the test tube reaches the boiling point and is still lower than the outside water temperature, and continues to absorb heat and boil.

2. Add salt to the water outside the test tube. After adding salt, the boiling point of brine is higher than the boiling point of water, the water temperature rises, and the water in the test tube reaches the boiling point and is still lower than the outside water temperature, and continues to absorb heat and boil.

3. Don't be idle and troublesome to operate, pump the test tube after it is sealed. The pumping pressure decreases, and the boiling point of the water in the test tube decreases and boils.

Speed up the boiling of water, yes.

1. Use a heat source with a higher temperature.

2. Capping (reduce evaporation and endothermy, so that the water is heated to boiling time shorter).

3. Reduce the quality of water.

The water in the tube in boiling water cannot boil because there will be no heat transfer when the temperature inside and outside the tube is equal.

Let It Boil:

1. Add some salt (such as sodium chloride) to the test tube, which can reduce the boiling point (the boiling point of NaCl solution is lower than that of water).

2. Pressurize the boiling water or depressurize the water in the test tube.

Speed up the boiling rate of water:

1. Use a container with a large bottom area to heat faster.

2. Water supply decompression.

3. Add salt to the water.

The experimental procedure for observing the boiling of water is as follows:

1 Pour an appropriate amount of warm water into the beaker, place the beaker on the asbestos net of the iron frame, and insert the thermometer into the water.

2 Heat the beaker with water with an alcohol lamp and pay attention to the thermometer.

3 When the temperature of the water rises to about 90, record the temperature of the water every 1 minute until the water boils and continue to heat for 4 minutes.

4 After the heating is stopped, continue to record the temperature of the water every 1 minute until the water temperature drops to about 96.

5. Record the experimental data in **.

The water heating time is relatively long, it may be that the initial temperature of the water is too low, or there is too much water, in order to reduce the experimental time, the initial temperature of the water can be increased; or reduce the quality of water, etc.

The temperature at which the water boils is not 100, it may be that the air pressure is not equal to 1 standard atmosphere; or impurities in the water; The thermometer is inaccurate, etc. The analysis is as follows:

1 Pour an appropriate amount of warm water into the beaker, place the beaker on the asbestos net of the iron frame, and insert the thermometer into the water.

2 Heat the beaker with water with an alcohol lamp and pay attention to the thermometer.

3 When the temperature of the water rises to about 90, record the temperature of the water every 1 minute until the water boils and continue to heat for 4 minutes.

4 After the heating is stopped, continue to record the temperature of the water every 1 minute until the water temperature drops to about 96.

5. Record the experimental data in **, the water heating time is relatively long, it may be that the initial temperature of the water is too low, or there is too much water, in order to reduce the experimental time, the initial temperature of the water can be increased; or reduce the quality of water, etc.

6. The temperature of water boiling is not 100, it may be that the air pressure is not equal to 1 standard atmosphere; or impurities in the water; The thermometer is inaccurate, etc.

If beaker. If the test tube is an opening, it is theoretically impossible to achieve. Because for water to boil, it must be satisfied:

Reaching the boiling point; Continue to heat. The temperature of the water in the beaker does not increase after boiling, and it is impossible to heat the water in the test tube with the skin mask. So in this case, the water in the tube cannot be boiled.

But if the beaker is sealed and the tube is open, it is possible to boil the water in the tube. Because the boiling point of the water in the beaker increases due to the increased sealing pressure, it is possible to be higher than 100 degrees Celsius.

The boiling point of the water in the test tube is still 100 degrees Celsius, so that the water in the test tube can boil. Or if the tube is tightly held and closed, the air pressure in the tube is less than the atmospheric pressure.

Then the water in the tube can be boiled in an aqueous beaker.

The former uses the principle that the boiling point of water rises when the air pressure increases, so that the boiling point of the water in the sealed beaker is higher than that of the water in the open test tube.

The latter uses the principle that the air pressure rises and decreases, and the boiling point of water decreases, so that the boiling point of the water in the sealed test tube is lower than the boiling point of the water in the beaker, so that the Kaihao water in the test tube boils.

The small water droplets formed by the liquefaction of the water vapor will collect at the bottom of the tube;

It can be seen from the figure that the index value of the temperature shortage denier meter is 1, and the value can be read according to the figure: 20 +8 = 28;

When water vapor meets cold, it forms small water droplets, which is a liquefaction phenomenon; Water boiling requires heat absorption, which is heat transfer; The combustion of alcohol is the conversion of chemical energy into internal energy, etc

So the answer is: (1) there is water (fog);

3) Liquefaction (heat transfer, boiling, liquefaction exothermic, heat transfer changes internal energy, vaporization, etc.).

a. Smoke is formed by solid small particles suspended lead floating in the air, and the phenomenon seen when the water is heated and boiled should be white fog, so A is wrong;

b. The crushing of gallium is a physical change, and the blue lumpy solid becomes a blue powdery solid, so B is wrong;

c. Copper sulfate reacts with sodium hydroxide to form a blue copper hydroxide precipitate, so it is correct;

d. Paraffin wax cannot be dissolved in water, so when it is put into water, the solid will not disappear, and it is wrong to be sensitive and boring; Therefore, C

As shown in the figure: the water in the large beaker absorbs the heat of the fire, can reach the boiling point, after reaching the boiling point, the temperature of the water is still lower than the temperature of the fire, and can continue to absorb heat, so the water in the beaker can boil At the beginning, the water in the test tube is lower than the temperature of the water in the beaker, and can absorb heat in the beaker, and after reaching the boiling point, the water in the beaker and the water in the test tube have the same boiling point because at the same atmospheric pressure, the water in the test tube can no longer continue to absorb heat, so it cannot boil

So the answer is: no; The water in the test tube reaches the boiling macro point and cannot continue to absorb heat

When the water in the large beaker boils, the temperature of the water in the beaker no longer rises, and the boiling point temperature of the water remains unchanged despite continuous heat absorption; The water in the small test tube absorbs heat from the large beaker, and after the temperature reaches the boiling point of the water, it cannot continue to absorb heat from the beaker just like the temperature of the water in the beaker, and although the boiling point is reached, it cannot absorb heat, so it will not boil

Therefore, choose B

When the water in the large beaker boils, the temperature of the water in the beaker no longer rises, and the boiling point temperature of the water remains unchanged despite continuous heat absorption; The water in the small test tube absorbs heat from the large beaker, and after the temperature reaches the boiling point of the water, it is the same as the temperature of the water in the beaker, and it cannot continue to absorb heat from the beaker, although the boiling point is reached, it cannot absorb heat, so it will not boil, so B is correct, and ACD is wrong

Therefore, choose B