You take a sample of water that is at room temperature and in contact with air and put it under a vacuum. Right away, you see bu
bbles leave the water, but after a little while, the bubbles stop. As you keep applying the vacuum , more bubbles appear. A friend tells you that the first bubbles were water vapor, and the low pressure had reduced the boiling point of water, causing the water to boil. Another friend tells you that the first bubbles were gas molecules from the air (oxygen, nitrogen , and so forth) that were dissolved in the water. Which friend is mostly likely to be correct? What, then, is responsible for the second batch of bubbles?
When pressure decreases, gas solubility decreases. The bubbles are gas molecules that were dissolved in the water at atmospheric pressure. The bubbles started coming out as a result of the decrease pressure. The second bubbles would be water vapor because as the pressure continue to decrease, the amount of vapor pressure ( vapor leaving the surface of the liquid ) equals the external pressure and water begin to boil. So the second bubbles must be water vapor.
Elements are substances that cannot be broken further down by chemical (or physical, for that matter) means. Sodium, tungsten, and iodine are all examples of chemical elements.
