MYP Biology: Water & It’s Properties

Water is Essential to Life on Earth It is the ONLY substance on Earth that can be found naturally-occurring in all states of matter… It makes up 60% of your body, 70% of your brain, and 80% of your blood… It covers more than 70% of the planet, but less than 3% of it is drinkable…

What is the Structure of a Water Molecule? H₂O 2 Hydrogen + 1 Oxygen These atoms are linked together by COVALENT bonds in which they share electrons

What is the structure of a water molecule? Hydrogen Atoms Covalent Bond Oxygen Atom

Water is a Polar Molecule A Polar molecule has positive and negative “poles” due to unequal sharing of electrons in Covalent bonds

Water is a Polar Molecule The larger atom(s) (Oxygen) pull more of the electrons toward it and takes on a negative (-) partial charge The smaller atom(s) (Hydrogen) have electrons pulled away from them and take on a slight positive (+) partial charge

Water makes Hydrogen Bonds Hydrogen bonds are between the oppositely charged ends of polar molecules (like water!)

Oxygen Atom Covalent Bond Hydrogen Atom Hydrogen Bond

Many Compounds Dissolve in Water Substances, like water, that other compounds dissolve in are called SOLVENTS. The compounds being dissolved in the solvent are called SOLUTES. Solutes and solvents mix together to form a SOLUTION.

A Solution: Salt & Water SOLUTE (Salt) SOLVENT (Water)

Many Compounds Dissolve in Water Polar solvents dissolve POLAR solutes Nonpolar solvents dissolve NONPOLAR solutes Polar & Nonpolar do NOT mix…

Some Compounds form ACIDS or BASES Acids release Hydrogen Ions (H+) when they dissolve in water Bases remove Hydrogen Ions (H+) when they dissolve in water

Higher than 7 = BASIC (Alkaline) Some Compounds form ACIDS or BASES The pH Scale identifies how basic or acidic a solution is. The scale runs from 0 to 14. Less than 7 = ACIDIC 7 = neutral Higher than 7 = BASIC (Alkaline)

more acidic stomach acid pH between 1 and 3

bile pH between 8 and 9 more basic

Water has many special properties ADHESION & COHESION Water molecules demonstrate ADHESION in their ability to stick to other surfaces and COHESION in their ability to stick to each other. This is due to the strong Hydrogen bonds they make.

Water has many special properties SURFACE TENSION The adhesive and cohesive properties of water produce SURFACE TENSION, or the ability of water molecules to form a thin surface ‘skin.’

Water has many special properties HIGH SPECIFIC HEAT Water changes temperatures very SLOWLY. This is because it requires a large amount of energy to disrupt water’s strong network of Hydrogen bonds.

Water has many special properties In most cases, the SOLID state of matter is the most dense: But water is a special case…

Water has many special properties SOLID Water is LESS Dense than LIQUID Water Due to the geometry of the Hydrogen bonds between water molecules, solid water (ice), is less DENSE than liquid water—so it floats!

Water has many special properties “UNIVERSAL” SOLVENT Since it is a POLAR molecule with neutral pH value, water is an excellent solvent and is able to dissolve most compounds.

Water’s properties make it essential to life Adhesion / Cohesion Water flows through tubes/ vessels from roots to tree-tops which allows plants to grow taller and transport water

Water’s properties make it essential to life Surface Tension Organisms can move across and live on top of bodies of water

Water’s properties make it essential to life High Specific Heat Stable environment for marine organisms Acts as effective coolant (sweating) Helps maintain homeostasis in terms of organism body temperature

Water’s properties make it essential to life Ice is less dense than liquid water (floats) Prevents water habitats from freezing solid Preserves liquid water in colder temperatures Ice reflects sunlight and regulates global temp.

Water’s properties make it essential to life “Universal” Solvent Dissolves and transports nutrients, gases, and waste through bodies of organisms and habitats

Check for Understanding! pH = 7 Acid, Base, or Neutral? pH = 3 pH = 13

Check for Understanding! Oxygen Atom Covalent Bond Hydrogen Atom Hydrogen Bond

Check for Understanding!

Check for Understanding! Hot Water + Hot Chocolate Mix = Hot Chocolate Solvent = Water Solute = Chocolate Mix Solution = Hot Chocolate

The End…