Chemistry

What floats and what sinks in water


Why do some bodies sink and others float in water? Let's look at some examples.

Water and oil do not mix. When a ship leaks oil, it causes major damage to nature. This is because oil does not sink. It floats on water, not allowing the passage of light essential for marine life.

If we put water in a container and inside it a piece of iron (nail), this iron will sink. Already if we put only an "empty" and capped bottle, the bottle will float. These examples show what density is.

In the first example, water is denser than oil. So what has the highest density is in the background. In the second example, the nail is denser than water, so it sinks. In the example of the empty bottle, it is actually full of air, which is less dense than water.

It is a relationship between the mass and volume of a substance. What weighs more? 1kg of cotton or 1kg of iron? The question leads one to think that the answer is 1 kg of iron because it is heavier, but in fact it is the densest.

Cotton and iron have the same mass (1kg), what will be different is the volume. A larger volume of cotton that corresponds to 1 kg and a very small piece of iron that corresponds to 1 kg. So:

denser - have greater mass at a given volume
less dense - have less mass at a given volume

d = m: v

Density table of some substances:

Substance

Density in g / cm³

Water

1

Ice

0,91

Alcohol

0,8

Petroleum

0,85

Acetone

0,80

Glass

2,6

wood

0,5

Mercury

13,6

Aluminum

2,7

Silver

10,5

Lead

11,4

Gold

19,3

Iron

7,8

Air

0,0013

Zinc

7,1

Sea water

1,03

Density is also related to the proximity of substance molecules. If we compare water molecules we will see that they are more united (more concentrated) than oil molecules, less united (less concentrated). So it can be said that water is denser than oil because its molecules are more united and so there are more water molecules compared in the same volume.

The dead sea

Dead Sea water is very salty. In it, there are almost no organisms, so the name Dead Sea. The presence of so much salt in this sea makes people not sink. Its density is 1.12g / mL, while the other seas have a density of 1.03g / mL.