Water Properties PDF

Unit 1: Chemistry of Life Chapter 1: Water © 2018 Pearson Education Ltd. The Molecule That Supports All of Life ▪ Water makes life possible on Earth ▪ Water is the only common substance to exist in the natural environment in al...

Unit 1: Chemistry of Life Chapter 1: Water © 2018 Pearson Education Ltd. The Molecule That Supports All of Life ▪ Water makes life possible on Earth ▪ Water is the only common substance to exist in the natural environment in all three physical states of matter ▪ Water’s unique emergent properties help make Earth suitable for life ▪ The structure of the water molecule allows it to interact with other molecules ▪ How does life on Earth depend on the chemistry of water? © 2018 Pearson Education Ltd.  Polar covalent bonds in water molecules result in hydrogen bonding ▪ In the water molecule, the electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen ▪ The water molecule is thus a polar molecule: The overall charge is unevenly distributed ▪ Polarity allows water molecules to form hydrogen bonds with each other © 2018 Pearson Education Ltd. Four emergent properties of water contribute to Earth’s suitability for life ▪ Four of water’s properties that facilitate an environment for life are ▪ Cohesion- Cohesive behavior ▪ Specific heat capacity-Ability to moderate temperature ▪ Expansion-Expansion upon freezing ▪ A Solvent-Versatility as a solvent © 2018 Pearson Education Ltd. 1. Cohesion of Water Molecules ▪ Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion ▪ Cohesion helps the transport of water against gravity in plants ▪ Adhesion is an attraction between different substances, for example, between water and plant cell walls © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. CAPILLARY ACTION ▪ The combined force of attraction among water molecules and with the molecules of the surrounding material. ▪ Cohesion + Adhesion ▪ Surface tension is a measure of how difficult it is to break the surface of a liquid ▪ Water has an unusually high surface tension due to hydrogen bonding between the molecules at the air-water interface and to the water below ▪ Walking on water © 2018 Pearson Education Ltd. Figure 3.3 Evaporation pulls water upward. H 2O Adhesion Two types of water-conducting cells Direction Cohesion of water 300 µm movement H 2O H 2O © 2018 Pearson Education Ltd. 2. Moderation of Temperature by Water ▪ Water absorbs heat from warmer air and releases stored heat to cooler air ▪ Water can absorb or release a large amount of heat with only a slight change in its own temperature © 2018 Pearson Education Ltd. Animation: Water Transport in Plants © 2018 Pearson Education Ltd. Water’s High Specific Heat ▪ The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC ▪ The specific heat of water is 1 cal/(g ∙ ºC) ▪ Water resists changing its temperature because of its high specific heat that can be traced to hydrogen bonding ▪ Heat is absorbed when hydrogen bonds break ▪ Heat is released when hydrogen bonds form ▪ The high specific heat of water minimizes temperature fluctuations to within limits that permit life. © 2018 Pearson Education Ltd.  Evaporative Cooling ▪ Evaporation (or vaporization) is transformation of a substance from liquid to gas ▪ Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas ▪ As a liquid evaporates, its remaining surface cools, a process called evaporative cooling ▪ Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water © 2018 Pearson Education Ltd. 3. Expansion Floating of Ice on Liquid Water ▪ Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense than water ▪ Water reaches its greatest density at 4ºC ▪ If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth © 2018 Pearson Education Ltd. Figure 3.6 Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Hydrogen bonds are stable © 2018 Pearson Education Ltd. 4. Water: The Solvent of Life ▪ A solution is a liquid that is a completely homogeneous mixture of substances ▪ The solvent is the dissolving agent of a solution ▪ The solute is the substance that is dissolved ▪ An aqueous solution is one in which water is the solvent © 2018 Pearson Education Ltd. Figure 3.8 Na+ – + + – – + – – Na+ – + + CI– CI– + – – + – + – – © 2018 Pearson Education Ltd. ▪ Water is a versatile solvent due to its polarity ▪ When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell © 2018 Pearson Education Ltd. ▪ Water can also dissolve compounds made of nonionic polar molecules ▪ Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions © 2018 Pearson Education Ltd. What property of water is shown? Hydrophilic and Hydrophobic Substances ▪ A hydrophilic (water-loving)substance is one that has an affinity for water ▪ A hydrophobic (water-hating) substance is one that does not have an affinity for water ▪ Oil molecules are hydrophobic because they have relatively nonpolar bonds ▪ Hydrophobic molecules related to oils are the major ingredients of cell membranes © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. Solute Concentration in Aqueous Solutions ▪ Most chemical reactions in organisms involve solutes dissolved in water ▪ When carrying out experiments, we use mass to calculate the number of solute molecules in an aqueous solution © 2018 Pearson Education Ltd. Acidic / basic conditions affect living organisms ▪ A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other ▪ The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+) ▪ The molecule that lost the proton is now a hydroxide ion (OH–) ▪ The molecule with the extra proton is now a hydronium ion (H3O+), though it is often represented as H+ ▪ Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed © 2018 Pearson Education Ltd. Figure 3.UN01 + – H H O H O O H O H H H H 2 H 2O Hydronium Hydroxide ion (H3O+) ion (OH–) © 2018 Pearson Education Ltd. ▪ Though statistically rare, the dissociation of water molecules has a great effect on organisms ▪ Changes in concentrations of H+ and OH– can drastically affect the chemistry of a cell ▪ Concentrations of H+ and OH– are equal in pure water ▪ Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH– ▪ Biologists use the pH scale to describe whether a solution is acidic or basic. © 2018 Pearson Education Ltd. Acids and Bases ▪ An acid is a substance that increases the H+ concentration of a solution ▪ A base is a substance that reduces the H+ concentration of a solution ▪ Strong acids and bases dissociate completely in water ▪ Weak acids and bases reversibly release and accept back hydrogen ions, but can still shift the balance of H+ and OH– away from neutrality © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. The pH Scale ▪ Acidic solutions have pH values less than 7 ▪ Basic solutions have pH values greater than 7 ▪ Most biological fluids have pH values in the range of 6 to 8 © 2018 Pearson Education Ltd. Figure 3.11 pH Scale 0 1 Battery acid Increasingly Acidic 2 Gastric juice (in stomach), lemon juice [H+] > [OH–] 3 Vinegar, wine, cola Acidic 4 Tomato juice solution Beer 5 Black coffee Rainwater 6 Urine Saliva Neutral 7 Pure water [H+] = [OH–] Human blood, tears 8 Seawater Neutral Inside small intestine solution Increasingly Basic 9 [H+] < [OH–] 10 Milk of magnesia 1 1 Household ammonia 12 Basic Household solution 13 bleach Oven cleaner 14 © 2018 Pearson Education Ltd. ▪ https://quizizz.com/admin/quiz/5d7bba9dba362b001 ab233f6/properties-of-water © 2018 Pearson Education Ltd.