Basic Chemistry Water Chemistry
Jan 12, 2016
Basic Chemistry
Water Chemistry
Atoms – 1 X 10-11
• Each atom is made up of a ‘nucleus’ and ‘orbits’ or ‘shells’ outside the nucleus Nucleus: Protons = + charged
Neutrons = neutral/ no charge
Orbits: Electrons = - charged
Periodic Table: A chart of elements that have been discovered
What makes each atom different, i.e. a unique element???
• Atomic number • The number of protons in nucleus • Electrons (-) will always equal protons (+)
• Atomic mass – The number of protons + neutrons in the
nucleus
Molecules = atoms bonded together = chemical bonds = represents ENERGY
wATER
METHANE
Ionic Bonds – between atoms that want to give and take electrons!
• “Happy” atoms = outer e- shells filled!
1. 2 e- fill first shell 1s What atom is this?
2. 8 e- fill second shell
1s 2s 2p What atom is this?
3. 8 e- fill third shell
?Q: Na and Cl … what would make them
Covalent Bonds = electrons shared
• CARBON
• Most common atom involved in covalent bonding
• ½ filled outer shell
(4 e-)
CH4 Methane gas
CompoundsNaCl – Sodium Chloride
- inorganic - ionic bonding - a salt
C6H12O6 - Glucose - organic
- covalent bonding- a sugar
Water Molecule: 2 Hydrogen and 1 Oxygen atom bonded
H20 - WATER
Oxygen side is slightly negative (-) charged
Hydrogen side is slightly positively charged (+)
Positive ends
Negative end
H H
O
“a polar-covalent molecule”
CAUSE and EFFECT
- Because of the ‘polarity’ of water molecules, they attract each other like magnets
• In this way, water molecules
“stick together” – cohesion
+-
-
+
+
+
Proof of the Cohesive nature of H2O …
- Certain insects can “walk on water”
- Cohesion between molecules of water
creates a strong surface tension
- benefits insects like the water strider
Adhesion - the tendency of two
DIFFERENT substances sticking together
Examples:
1. water molecules “sticking” to glass
2. capillary action
Capillary Action - example of adhesion
- water molecules adhere to the inside of tubules that fill the stems of plants
- water molecules are “drawn up” from the soil toward the top of the tree by the pull of adhesion
• Perspective: the size of “A” water molecule
– A molecule of water is so small that there are millions of molecules in a single drop of water.
– About 60 million water molecules could be stretched side by side across a penny.
Water• is the ONLY compound that commonly
exists in all 3 phases (solid, liquid, gas) on earth
• there would be no life on earth without water.
WATER … the Universal Solvent
In a SOLUTION, - the solvent is the substance that does
the dissolving ( usually a liquid)
- the solute is the substance that is dissolved (usually a solid)
- so many substances are soluble in water that it is therefore called the …
“universal solvent”
WATER … in living cells
- is the SOLVENT of our cells’ cytoplasm
- dissolves the SOLUTES: carbs, lipids, proteins
3 types of environments living cells encounter
• ISOTONIC environment
Equal amounts of solvent and solute molecules inside and outside of cells
• HYPERTONIC environment
– Greater % of solute molecules in sol’n outside the cell to
inside
• HYPOTONIC– Less % of solute molecules in the sol’n
outside the cell to inside
In Solutions … … water molecules disassociate into
1. H + ions and
2. OH- ions
THE pH Scale- a scale that measures the concentration of
H+ ions in the solution compared to OH- ions
1. An acidic solution (pH range 0 – 6.9)- a high concentration of H+ ions
- ( Infer: a low concentration of OH- ions )
Sulfuric acid
H2SO4
Citric AcidHC6H7O7
2. An alkaline solution - pH range 7.1 – 14 (also known as ‘bases’) - a low concentration of H+ ions compared to OH - ions
Sodium HydroxideNaOH Calcium carbonate
CaCO3
Sodium Bicarbonate
NaHCO3
• The pH scale ranges from 0 to 14
• The pH of pure water is 7 = equal amounts of H+ and OH- ions
Water Chemistry Terms
A. Hydrolysis- a chemical reaction where water
molecules are used to break up a large compound into smaller ones
B. Dehydration Synthesis- a chemical reaction where water
molecules are taken away from smaller molecules in order to form a larger compound.
Water Chemistry TermsC. Hydrophobic
- substances that will not dissolve in water
- Ex. fats, oils, soaps … “non-polar” substances
D. Hydrophilic - substances that will dissolve in water
• - Ex. sugar, salt, tea, protein powder - “polar” substances - “LIKE DISSOLVES LIKE”
Water’s UniquenessA. For most substances, their solid form is more
dense than the liquid formB. But for water the solid form is less dense than the liquid form. Proof: Ice floats on water!
WHY is ice less dense than water/steam? water as a solid
- the molecules “line up” - geometrically organized molecules
water as a liquid or gas
- molecules are random, in constant motion
- very close together
Pond Temperatures
VII. Water: Public Health Issues
A. Open Sewers
- Before the invention of sewer systems, human and animal waste was collected in open water ways.
- How many of the earth’s 6 billion people still live with these open sewers?
ANALYZE: Open Sewer Consequences
- breeds disease – why?
- contaminates drinking water – how?
- Hurricane Katrina “undid” the sanitation system … how?