Water Chemistry and Acid/Base Review

Hydrogen bond H O H  –  +  –  +  –  +  –  + —— —— Fig. 3-2 Figure 3.2 Hydrogen bonds between water molecules  –  +

2. 1. 3. Name 3 properties of water illustrated in this picture. Fig. 3-3 2. This slide shows 3 properties of water: Cohesion (1), Adhesion (2), and Capillary Action (3) Water-conducting cells 3. Capillary action Involves 1 and 2. Direction of water movement 1. Figure 3.3 Water transport in plants 150 µm Name 3 properties of water illustrated in this picture.

Fig. 3-4 Surface tension: The measure of how hard it is to break the surface of a liquid. This property is related to cohesion. Figure 3.4 Walking on water

Hydrogen bonds are stable Liquid water Fig. 3-6 Hydrogen bond Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Figure 3.6 Ice: crystalline structure and floating barrier

The Solvent of Life A solution is a liquid that is a homogeneous mixture of substances A 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

– – – – – – – – – – – + + + + + + + + + + Fig. 3-7 Note how the water molecules turn themselves so that the opposite charged part of the water is facing the ion. Water is pulling the sodium ion from the chloride ion and breaking the ionic bond. Salt will then dissolve. – Na + + + – – + – – Na + – + + Cl– Cl– + – – + – + – Figure 3.7 Table salt dissolving in water –

2H2O Hydronium Hydroxide ion (H3O+) ion (OH–) Fig. 3-UN2 Water “tugs” on other water molecules. Sometimes one water may pull a hydrogen proton away from another water The hydrogen proton Pulled away left behind its electron. We now have hydroxide (OH-). H H O H O O H O H H H H 2H2O Hydronium ion (H3O+) Hydroxide ion (OH–) “Mutilated” Mouse – missing an “ear” or hydrogen proton. What to remember: this solution has more OH- ions than H+ ions. Solution is basic: pH greater than 7. Hydronium = “Mutated Mouse” - It has 3 “ears”. What to remember: a solution in this state would have more H+ ions than OH- ions and would be acidic with a pH less than 7.

Acids and Bases An acid is any substance that increases the H+ concentration of a solution A base is any substance that reduces the H+ concentration of a solution (therefore bases have more OH- ions in the solution) pH means potential hydrogen. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Figure 3.9 The pH scale and pH values of some aqueous solutions 1 Battery acid Gastric juice, lemon juice 2 H+ H+ H+ H+ OH– 3 Vinegar, beer, wine, cola OH– H+ H+ Increasingly Acidic [H+] > [OH–] H+ H+ 4 Acidic solution Tomato juice Black coffee 5 Rainwater 6 Urine OH– Saliva OH– Neutral [H+] = [OH–] H+ H+ OH– 7 Pure water OH– OH– H+ Human blood, tears H+ H+ 8 Seawater Neutral solution 9 Figure 3.9 The pH scale and pH values of some aqueous solutions 10 Increasingly Basic [H+] < [OH–] Milk of magnesia OH– OH– 11 OH– H+ OH– OH– Household ammonia OH– H+ OH– 12 Basic solution Household bleach 13 Oven cleaner 14

Buffers The internal pH of most living cells must remain close to pH 7 Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution Carbonic acid Bicarbonate ion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings