Laboratory Notes: Water - Part 1 PDF

Wonderful Water!!! 1 Water: Background Water is essential to all life on Earth. 71% of Earth’s surface is currently covered in water. Oceans hold 96.5% of Earth’s water. Rest of water exists as: ✓ Freshwater in rivers and lakes ✓ Frozen water in glaciers and ice caps ✓ S...

Wonderful Water!!! 1 Water: Background Water is essential to all life on Earth. 71% of Earth’s surface is currently covered in water. Oceans hold 96.5% of Earth’s water. Rest of water exists as: ✓ Freshwater in rivers and lakes ✓ Frozen water in glaciers and ice caps ✓ Soil moisture and GROUNDWATER AQUIFERS ✓ WATER VAPOR in ATMOSPHERE 2 Water: Background Water is special. Water only molecule on earth occurring naturally as solid, liquid & gas (i.e., in three PHASES or PHYSICAL STATES). Currently, around this very college, water exists as a SOLID (ice, snow), LIQUID (rain, SURFACE WATER, GROUNDWATER) and GAS (water vapour, humidity). SURFACE WATER: water located on top of land and surrounded by land (e.g., stream, rivers, lakes, wetlands). GROUNDWATER: water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. SEAWATER: water from a SEA or OCEAN. 3 Water: Background Definitions to ensure complete understanding: MOLECULE: two or more ATOMS connected/ bonded together. Water, H2O, is a MOLECULE as it consists of 3 atoms bound together. PHYSICAL STATES: ✓ SOLID ✓ LIQUID ✓ GAS ✓ AQUEOUS (i.e., dissolved in water) 4 Water: Some Numbers Water is main component of most CELLS. High percentages of our bodies are made up of water: ✓ Newborn babies: 78% water ✓ 1 year old infant: 65% water ✓ Adults: 55 – 60% water (fat holds less water than muscle, so amounts vary). ✓ % water drops with age. Consider different organs: ✓ lungs: 83% water ✓ kidneys: 79% water ✓ brain: 73% water % water in our bodies drops with age. ✓ heart: 73% water 5 Water: Some Numbers Now back to GEOLOGY: FRESHWATER: water containing less than 1,000 milligrams per liter of dissolved solids, most often salt. Less than 3% of Earth’s water is FRESHWATER. Of that 3%: > 68% found in glaciers/ice caps > 30% found in GROUNDWATER 0.3% found in SURFACE WATER! So most accessible drinking water comes from 0.3% of 3% of Earth’s water! More than 99% of Earth’s water is not usable for drinking unless we use VARIOUS technologies (desalination, dig wells, etc…). 6 Water: Some Numbers Some fun facts: Canada has abundant freshwater resources. About 20% of world’s fresh SURFACE WATER in Canada. Canada’s lakes and rivers cover 12% of surface area. Canada has more “lake area” (area covered by lakes) than any other country in world. Great Lakes (Canada/USA) contain 18% of global fresh SURFACE WATER. 25% of Canadians depend on GROUNDWATER Canada has abundant freshwater resources. for drinking water, including Adamo ☺. 7 Water: Essential Concepts EACH DOT = 1 ELECTRON To fully understand water, this most precious of EACH LINE = resources, we must examine some key concepts. 2 ELECTRONS BEING SHARED These include (but are not limited to): ✓ Intermolecular forces (HYDROGEN-BONDING) ✓ Phase changes ✓ Solutions and Solubility ✓ pH Scale A water molecule. Note how water molecules have a bent shape. 8 Water: Essential Concepts Atoms within a single water molecule bond together by sharing electrons. EACH DOT = 1 ELECTRON They form 2 OXYGEN (O) – HYDROGEN (H) EACH LINE = COVALENT BONDS. 2 ELECTRONS BEING SHARED COVALENT BOND: BOND formed when share 2 electrons. Atoms in water molecule held together by COVALENT BONDS. INTRAMOLECULAR BONDING: bonding between atoms occurring within a molecule (i.e., “intra” = within molecule). 9 Water: Essential Concepts Also important to consider interactions between multiple water molecules (i.e., interactions occurring between multiple water molecules). Between water molecules, we encounter weaker but extremely important interactions known as INTERMOLECULAR FORCES (i.e., “inter” = between molecules) INTERMOLECULAR FORCES: relatively weak interactions that occur between molecules. Important INTERMOLECULAR FORCES exist between water molecules. INTERMOLECULAR FORCES keep water molecules together to a certain extent. 10 Water: Essential Concepts Consider a water molecule (H2O). Can encounter H2O as solid (ice, snow), liquid (liquid water) or gas (water vapour). When change state (e.g., solid to liquid, etc), individual molecules remain intact/remain H2O. Molecules do NOT come apart. What changes when change PHYSICAL STATE is INTERMOLECULAR FORCES between molecules. Nothing changing within molecules. When change state (e.g., solid to liquid, etc), Let us consider INTERMOLECULAR FORCE individual molecules remain intact/remain H2O. between water molecules in more detail. 11 Water: Essential Concepts Water is a POLAR MOLECULE. Remember that ELECTRONS have a negative charge. Oxygen likes to “HOG” electrons. Even though it’s supposed to share electrons with hydrogen (in forming COVALENT BONDS), it pulls “shared” electrons closer to itself. As a result, oxygen in water is ELECTRON-RICH, while two hydrogens are ELECTRON-POOR. In same way as Earth has 2 POLES (a North Pole and a South Pole), water also has 2 POLES (an ELECTRON- oxygen in water ELECTRON-RICH, RICH pole and an ELECTRON-POOR pole. two hydrogens are ELECTRON-POOR. Therefore, water is POLAR! 12 Water: Essential Concepts Remember that ELECTRONS have a negative charge. Oxygen in water is “PARTIALLY NEGATIVE” as it holds electrons closer to itself. Hydrogens in water are “PARTIALLY POSITIVE” as the oxygen is pulling their electrons away. In science, “partially” is represented by the Greek letter delta, δ. We say oxygen is “PARTIALLY NEGATIVE” or δ-. oxygen in water ELECTRON-RICH, two hydrogens are ELECTRON-POOR. We say hydrogen is “PARTIALLY POSITIVE” or δ+. 13 Water: Essential Concepts DIPOLE = 2 POLES. In DIPOLE-DIPOLE ATTRACTION, molecules As we have seen, water has 2 poles (one PARTIALLY maximize attractive POSITIVE-NEGATIVE POSITIVE, one PARTIALLY NEGATIVE). interactions and minimize repulsive POSITIVE- POSITIVE and NEGATIVE-NEGATIVE interactions. Remember that OPPOSITES ATTRACT (positive and negative attract one another). Molecules find best compromise between attraction and repulsion Water molecules are attracted to one another through in positioning DIPOLE-DIPOLE ATTRACTION. themselves. DIPOLE-DIPOLE ATTRACTION: attractive force experienced when POLAR molecules line up so that PARTIALLY POSITIVE end of one molecule lines up with/is close to PARTIALLY NEGATIVE end of another molecule. 14 Water: Essential Concepts Water molecules undergo a specific DIPOLE-DIPOLE INTERACTION: HYDROGEN BONDING. What is hydrogen bonding? Note how repulsions being minimized, 2 oxygen atoms or 2 hydrogen atoms not interacting. HYDROGEN BONDING. 15 Water: Essential Concepts ELECTRONEGATIVE ATOMS: Atoms that like to pull electrons towards themselves. Note how repulsions being The most ELECTRONEGATIVE ATOMS: Oxygen, minimized, 2 oxygen atoms Nitrogen, Fluorine. or 2 hydrogen atoms not interacting. Whenever hydrogen is bound to very ELECTRONEGATIVE oxygen, nitrogen or fluorine atoms within a molecule, we encounter very strong HYDROGEN-BONDING interactions between individual molecules. HYDROGEN BONDING. In water, hydrogen is bound to ELECTRONEGATIVE oxygen. Therefore, we have HYDROGEN BONDING. 16 Water: Essential Concepts OVERALL: A DIPOLE-DIPOLE ATTRACTION involving molecules containing hydrogen bound to a VERY electronegative oxygen, nitrogen or fluorine atom is known as HYDROGEN BONDING. HYDROGEN BONDING: unusually strong DIPOLE-DIPOLE attractions occurring among molecules containing hydrogen bonded to highly electronegative oxygen, nitrogen or fluorine atoms. HYDROGEN BONDING has an enormous impact on the way water behaves! For more on hydrogen bonding and water, watch this video! https://www.youtube.com/watch?v=HVT3Y3_gHGg 17 Water: Phase Changes Again: Water only molecule on earth occurring naturally as solid, liquid & gas (i.e., in three PHASES or physical states). When a substance (e.g., water) undergoes a PHASE CHANGE (e.g., changes from solid to liquid or liquid to gas) molecules remain INTACT. Changes in state (i.e., PHASE CHANGES) are due to changes in the forces between molecules (i.e., INTERMOLECULAR FORCES) rather than in those within the molecules. Do you recall the names for all the PHASE CHANGES we can encounter? 18 Water: Phase Changes PHASE CHANGES: 19 Water: Phase Changes Lucky for us, ice is LESS dense than liquid water!!! 20 Next Lecture: More Water, We need more Water!!! 21