Properties of Water

Water a unique polar covalent molecule necessary for life found in all cells and around all cells

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? Ionic and covalent bonds hold together substances Hydrogen bonds are attractions between separate molecules

Universal Solvent “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

Universal Solvent Solution –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 Salts and Solubility

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).

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

Water & Solutions Figure 5, page 31 Holt Biology Hydrogen Bonding in Water 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 –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

Density of Water (H 2 O) 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

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

High Specific Heat water has a high specific heat (heat capacity) –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) –specific heat – the amount of heat required to raise 1 gram of a substance 1 degree Celsius it takes a lot of energy to heat up or cool down water

Neutral pH Pure water will ionize in the following way to create hydrogen, and hydroxide ions. H2OH2OH+H+ + OH - water hydrogen ion hydroxide ion

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 be harmful to life

Water & Solutions

This may make you uncomfortable!!!

Damage to Life Acid HF Hydrofluoric acid Base NaOH Sodium hydroxide

More on pH later…