The Chemistry of Water

A water molecule, is made of three atoms, two hydrogen’s and an oxygen. Water has some unique characteristics that make it vital for life.  So let’s learn about the chemistry of water.

water

  • The hydrogen’s carry a positive charge and the oxygen a negative charge, which causes the different molecules to cling to each other in a hexagonal shape. Snowflakes always form in hexagons because water, at the molecular level, forms in hexagons.

    This is a picture of a snowflake, magnified and captured on film by Wilson Bentley. Public domain.

  • When water freezes it expands, unlike almost any other known substance. Normally molecules grow closer together as they lose heat, but water is less dense as a solid, because of the attractions and the structure between the molecules due to the charged nature of the O’s and H’s. If this were not the case, ice would sink and the bottom of all the oceans and lakes would remain in a perpetually frozen state, radically altering the climate to one completely inhospitable to life.
  • Water is known as the universal solvent, because it dissolves so many different substances. This is vital, because it is water that carries minerals around the globe giving vital nutrients where they are needed and allowing them to be used by plants and animals.

Here are some experiments to try with water:

Freezing Salt Water

  1. Get two cups, fill them each about halfway with water from the tap.
  2. Add 2 T. salt to one cup and label it to keep track.
  3. Put both cups in the freezer.
  4. Check back on them a couple of hours later.
  5. Which cup froze better? Why do you think it works this way? Think about the oceans and compare your find to what happens there.

A frozen sea near Estonia. Photo by Guillaume Speurt from Vilnius, Lithuania, CC license, Wikimedia.

 Surface Tension

  1. Fill a cup to the very top with water.
  2. Now use an eye dropper to put one drop at a time in the cup until the water bulges over the top.
  3. Molecules of water are charged, causing them to cling together, so the water can actually be higher than the top of the cup.

Science experiments with water, including surface tension, sublimation, and more.

Sublimation

Have you ever noticed that ice cubes left in the freezer for a really long time get smaller and smaller? Or that the snowbanks on the side of the road in winter shrink even when the weather stays cold? That’s sublimation. Solids can turn straight into gases, without ever being liquid in the middle, but it happens much slower than melting or evaporation on a hot day.

This is a picture of dry ice, liquid carbon dioxide, sublimating from a solid directly to a gas. This process happens much faster than water sublimation. Photo by Mikk Mihkel Vaabel, CC license, Wikimedia.

Put some water in your freezer in a long thin tube, like a plastic graduated cylinder.  Leave it uncovered.  Mark how high the ice is a day after you freeze it.  Mark it once a week for a month and see if you can detect sublimation.

A dry ice sublimation experiment.

Spaces in a Liquid

  1. Measure exactly one cup of water in a 2 cup liquid measuring cup.
  2. Measure exactly one cup of rubbing alcohol in a liquid measuring cup.
  3. Predict how much liquid it will be when poured together.
  4. Pour the alcohol into the water.
  5. What is the total measurement? Why?
  6. Liquids are dense, but there are still spaces between the molecules. Some of the alcohol molecules (OH-) fit in between the water molecules, so you end up with less than 2 cups total.
  7. Try this again, using one cup of water and one cup of sugar. What happens?

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