Characteristics of Water

Water a unique polar covalent molecule so necessary for life that it is found in all cells and around all cells chemical formula of water = H2O two hydrogen atoms and one oxygen atom

What do these have in common? They are polar. They have oppositely charged ends

This is called polarity.

This is called polarity. Water also has oppositely charged ends.

Polarity an uneven distribution of shared electrons within a molecule causing slight opposite charges on opposite ends of the molecule

Hydrogen Bonds a WEAK chemical attraction between polar molecules the attraction between the positively charged hydrogen of water and the negative charge that exists on other polar molecules including water itself due to water’s polarity

Hydrogen Bonds

How are hydrogen bonds different than ionic and covalent bonds?

How are hydrogen bonds different than ionic and covalent bonds? Ionic and covalent bonds hold together substances and are STRONG (shown with solid lines) Hydrogen bonds are attractions between separate molecules and are WEAK (shown with dotted lines)

Universal Solvent water is able to dissolve many compounds – “like dissolves like” water is able to dissolve compounds with charges water is able to dissolve ionic compounds and other polar compounds, but not nonpolar compounds

Why is it important that water can dissolve many substances? wherever water goes (either through the ground or through our bodies), it carries valuable chemicals, minerals, and nutrients

Universal Solvent Solution Solute Solvent mixture of two or more substances in which the solute molecules are evenly distributed in the solvent Ex: salt water, sugar water, antifreeze Solute substance that is dissolved Ex: salt, sugar, food coloring Solvent substance that does the dissolving Ex: water, acetone

Water & Ionic Substances Why is water able to dissolve salt?

Water & Ionic Substances Salt is ionic (made of charged particles) and water is polar (has charged ends).

Water & Ionic Substances Click here  Salts and Solubility Click “Download” Then click “Open” or “Run” Shake the salt shaker to add pieces of salt to the water. Continue to shake and add salt until you see salt build up on the bottom of the container.

Water & Ionic Substances Why are the ions moving in the water? The invisible water molecules are constantly moving. How could we get the molecules of water moving faster to dissolve more salt? Heat up the water.

Water & Polar Substances Why is water able to dissolve sugar?

Water & Polar Substances Sugar is polar (has charged ends) and water is polar (has charged ends).

Water & Nonpolar Substances Why does vegetable oil separate from water when they are mixed in the same container?

Water & Nonpolar Substances Why does vegetable oil separate from water when they are mixed in the same container? Vegetable oil is nonpolar (no charged ends), and water is polar (has charged ends).

Water & Nonpolar Substances

Cohesion and Adhesion Cohesion Adhesion attraction between molecules of the same substance Adhesion attraction between molecules of different substances

Water & Solutions Is this cohesion or adhesion? Hydrogen Bonding in Water Figure 5, page 31 Holt Biology Is this cohesion or adhesion?

Surface Tension property of the surface of a liquid to resist an external force the surface can stretch and will not break easily

Surface Tension

Surface Tension property of the surface of a liquid to resist an external force the surface can stretch and will not break easily caused by cohesion

Water & Solutions Surface Tension

Capillary Action process in which water molecules move up through a narrow tube the attraction of water to the walls of the tube and to the other water molecules around it pulls the water up more strongly than gravity pulls it down caused by adhesion and cohesion

Water & Solutions Capillary Action

Water & Solutions Capillary Action

Water & Solutions Capillary Action

Capillary Action

Density of Water (H2O) liquid water has a density of 1 g/mL

Density Anomaly water is rare in that its solid form (ice) is less dense than its liquid form water

Density Anomaly

Density Anomaly water is rare in that its solid form (ice) is less dense than its liquid form water ice floats in water

Specific Heat the amount of heat required to raise 1 gram of a substance 1 degree Celsius

WHY?!?!

High Specific Heat water has a high specific heat (heat capacity) it takes a lot of energy to heat up or cool down water

Neutral pH Pure water will ionize (split into ions) to create hydrogen and hydroxide ions. H2O H+ + OH- water hydrogen ion hydroxide

Neutral pH because of this, water has a neutral pH pH – a system to measure the concentration of H+ ions in a solution acids and bases can damage living tissues

Water & Solutions

This may make you uncomfortable!!!

Damage to Life Acid HF Hydrofluoric acid Base NaOH Sodium hydroxide

More on pH later…