# Does pure water freeze at 0? C.

### Quick-change artist water

It is well known that water is liquid. However, this is not always the case. In nature, water occurs in three states: as liquid water, as gaseous water vapor or as solid ice. Depending on the external conditions, it passes from one state to the other.

The state of the water depends on the pressure and its temperature. If liquid water exceeds the boiling point, it evaporates and floats in the air as gaseous water vapor. Even when evaporating at room temperature, water changes into a gaseous state. However, this happens more slowly than when evaporating. If, on the other hand, the temperature drops below 0 ° Celsius, the water freezes to ice. As soon as water changes its state between liquid, gaseous or frozen, it changes its properties.

The special thing about water is that it has its greatest density at 4 ° Celsius and takes up little space. When it freezes into solid ice, it expands and increases in volume. At the same time, its density decreases. That is why ice is lighter than water with the same volume. That is why icebergs can drift in the sea. For the same reason, a lake freezes over from above and not from below in winter. That's a good thing, because otherwise we wouldn't be able to skate until the lake was completely frozen from bottom to surface.

So water expands when it freezes. If you prevent it from doing so, there is tremendous pressure on it. Anyone who has ever forgotten a bottle of water in the freezing cold outside knows the consequences: after a while the bottle bursts and the ice oozes out. In this way, ice can also break up stone. This happens when water flows into cracks in the rock, freezes there and pushes outwards due to the expansion. If pieces of stone flake off as a result of this force, it is called frost splitting. Anyone who has ever driven into a pothole knows the consequences. Here the constant alternation of wetness and frost have really damaged the asphalt.

### What water can do

No matter whether we drink tap water, jump into a lake or are surprised by a downpour - we are constantly in contact with water. And not only that: we are made of water ourselves, around two-thirds of it. Without question, water is part of our everyday life. But what seems quite normal to us has all kinds of peculiarities. And the water owes this primarily to its structure.

Everything that exists on this earth is made up of tiny building blocks, the atoms. This is also the case with pure water: It is a combination of two hydrogen atoms and one oxygen atom. These combine to form a water molecule, H for short2O. The individual water molecules are only loosely connected to one another.

This loose cohesion ensures that the connection between the molecules breaks at high temperatures: the water evaporates. If, on the other hand, it cools down significantly, the molecules organize themselves into a solid, regular lattice, the ice. The special thing about it: In its solid form, water has a larger volume than in its liquid state.

The arrangement of the water molecules also ensures another property: the surface tension of the water. Because of this tension, water spiders and water striders can easily walk on a pond. But water can do even more: it is able to dissolve substances. Small grains of salt or sugar dissolve completely in water. Sea water, for example, contains large amounts of salt that we can taste but not see.

We owe the fact that lemons ripen on the island of Mainau on Lake Constance to another ability of water: it can store heat. Lakes or seas heat up in summer and keep the heat for a long time. That is why the temperatures on the coast fluctuate less than inland. Far from the coast, the temperature differences between day and night and between summer and winter are much greater than near the sea.

### The water cycle

The water on earth is always on the move. Huge amounts of it are constantly moving - between sea, air and land - in an eternal cycle in which not a single drop is lost.

The motor of the water cycle is the sun: It heats the water of the seas, lakes and rivers so much that it evaporates. Plants also release water vapor into the atmosphere through tiny openings. The humid air rises, tiny water droplets gather in the air and form clouds. As rain, hail or snow, the water falls back into the sea or onto the earth. If it falls on the ground, it seeps into the ground, supplies plants or flows through the ground, via streams and rivers back into the sea. The eternal cycle of evaporation, precipitation and runoff starts all over again.

The water cycle has been around for almost as long as the earth has existed. He ensures that living beings on our planet are supplied with fresh water. And not only that: Without the water cycle, the weather as we know it would not exist.

### constant dripping wears away the stone

Deep gorges in the mountains, wide sandy beaches by the sea and wide rivers that meander through meadows and fields - all of these are landscapes that we know well. Because they are so varied, we find them impressive and beautiful.

The sculptor of all these landscapes is the water cycle. Sooner or later, water shapes the surface of the earth more strongly than any other force. It washes away soil after a downpour. It digs into the ground and loosens parts of the rock. It carries earth and weathered rock debris with it down into the valley. Where the water drains off more slowly, it lets go of its burden of silt, sand and rubble. When there is high water it floods the flat areas of a valley, the river floodplains. Here, too, it deposits fine mud. When the water finally flows into the sea, it works the coasts and forms very different landscapes, for example cliffs or long sandy beaches.

Water also shapes the landscape in the form of ice. If water freezes in cracks in the stone, it bursts the stone. As a glacier, it planes out notch-shaped river valleys to form round trough valleys. And the moraine landscape in the foothills of the Alps with its boulders and boulders is the result of glaciers that formed the subsoil a long time ago.

### Where do icebergs come from?

Although icebergs are floating in the sea, they are not made of frozen sea water, but of fresh water. Because they come from the huge glaciers of the polar regions. The polar glaciers protrude into the sea at the edges. Pieces of them break off regularly - the icebergs. It is also said that the glacier “calves”. And because ice is lighter than water, it drifts around in the sea without sinking.

The polar seas are cold between –4 and 0 degrees Celsius. That is why the icebergs only thaw very slowly. When the current drives them into warmer waters, they melt a little faster. Nevertheless, large icebergs live to be decades old.

Some icebergs are huge and flat: the tabletop icebergs. They arise when the glaciers on the coast slide far out into the sea. Then large ice sheets float on the sea, but they are still connected to the glacier. This “ice shelf” can be between 200 and 1,000 meters thick. The largest areas of ice shelf are in Antarctica, on the coasts of Greenland and Alaska. When large pieces of ice break off, they swim out into the polar sea as tabular icebergs.

Icebergs are very dangerous for shipping because only their tip is visible above water. Most of the iceberg is underwater. Ships must keep a sufficiently large safe distance from the white giants so that they are not damaged by the sharp edges of the iceberg.

But there is also ice that freezes from sea water: First, ice floes from salt water form on the surface of the water. When these ice floes are pushed together, a coherent ice sheet is created - the pack ice.

23.8.2008

A bathtub full of water to make a cup of coffee - that's 140 liters! Almost as much water is needed for a breakfast egg. Nonsense? The British geographer Anthony Allan has stated otherwise. At the Stockholm World Water Week, he and the WWF (World Wide Fund for Nature) drew up an astonishing calculation for water consumption.

Your calculation is not just about the one cup of water that is poured into the coffee machine, but the total amount of water that is necessary to produce one cup of coffee. And that begins with the cultivation of the coffee plant, which has to be watered intensively. Water is also used in the transport and packaging of the coffee. If you add everything up, you get an initially unbelievable 140 liters of water for a single cup.

But the calculation goes even further. A T-shirt contains 4,100 liters of water, a new car swallows around 400,000 liters. In this way, every German consumes around 4,000 liters of water per day. This includes water consumption such as drinking or washing as well as consumption in the manufacture of products. Each of us leaves such a water “footprint”, depending on how much water we personally use. Because a large part of this consumed water is not visible, it is also called "virtual water". According to this calculation, we take almost 30 full baths per day - purely virtual!

### Aral Sea dried up

It was once the fourth largest lake on earth. But compared to its former size, the Aral Sea in Central Asia is now just a puddle, surrounded by a barren desert landscape. The reason: huge cotton fields in Kazakhstan and Uzbekistan. Artificial irrigation is needed to grow cotton in this dry area. The farmers have therefore tapped the two large tributaries Amu-Darja and Syr-Darja of the Aral Sea since the 1930s and diverted the water to their fields. The result: the Aral Sea continued to dry up. As the amount of water decreased, the lake also became increasingly salty. This also had an impact on the animal world: Of the more than 30 species of fish that were once, only six are now found in the salty lake.