CELL COMPOUNDS Water Acids, Bases & Buffers Water Acids, Bases & Buffers

Thought Question: Can life exist without water? Why is water so important to life as we know it? Can life exist without water? Why is water so important to life as we know it?

Learning Outcomes: B2 - Describe the characteristics of water and its role in biological systems –Describe the role of water as a solvent, temperature regulator and lubricant –Describe how the polarity of the water molecule results in hydrogen bonding B3 - Describe the role of acids, bases and buffers in biological systems in the human body –Differentiate among acids, bases and buffers –Describe the importance of pH to biological systems in the human body B2 - Describe the characteristics of water and its role in biological systems –Describe the role of water as a solvent, temperature regulator and lubricant –Describe how the polarity of the water molecule results in hydrogen bonding B3 - Describe the role of acids, bases and buffers in biological systems in the human body –Differentiate among acids, bases and buffers –Describe the importance of pH to biological systems in the human body

Water Water is one of the most important compounds for living organisms Many unique and important properties of water are a result of the structure of water molecules (polarity and hydrogen bonding) Water is one of the most important compounds for living organisms Many unique and important properties of water are a result of the structure of water molecules (polarity and hydrogen bonding)

Functions of Water in the Body Lubricant – in digestive system, brain and spinal cord, joints, eyes, etc. Facilitates chemical reactions – ex. Digestion Transport of materials – many substances are able to dissolve in water ex. Nutrients in blood Water helps to regulate temperatures in the body Lubricant – in digestive system, brain and spinal cord, joints, eyes, etc. Facilitates chemical reactions – ex. Digestion Transport of materials – many substances are able to dissolve in water ex. Nutrients in blood Water helps to regulate temperatures in the body

Structure of Water molecules The oxygen and hydrogen atoms are held together by covalent bonds

Polarity of Water Molecules The oxygen end of the water molecule attracts electrons more strongly than the hydrogen end Results in a slight negative charge at the O end, and a slight positive charge at the H end The oxygen end of the water molecule attracts electrons more strongly than the hydrogen end Results in a slight negative charge at the O end, and a slight positive charge at the H end

Hydrogen Bonds The positive end of one water molecule is attracted to the negative end of another molecule Weak bonds called hydrogen bonds are formed between molecules The positive end of one water molecule is attracted to the negative end of another molecule Weak bonds called hydrogen bonds are formed between molecules

Hydrogen Bonds

Special Properties of Water Liquid at room temperature “universal solvent” Cohesive (sticks to itself) Adhesive (sticks to other things) Temperature changes slowly High heat of vaporization Less dense in solid form than liquid Liquid at room temperature “universal solvent” Cohesive (sticks to itself) Adhesive (sticks to other things) Temperature changes slowly High heat of vaporization Less dense in solid form than liquid

All of these properties are related to the polarity of the water molecule and the hydrogen bonding between the molecules

Assignment : Refer to pages in your text For the first 4 items listed under “Water has Unique Properties” do the following: –Property (copy from the numbered points in the book) –In your own words explain: how this property is related to hydrogen bonding and/or polarity (diagrams might help) why this property is important to living organisms (and specifically, in the human body) Refer to pages in your text For the first 4 items listed under “Water has Unique Properties” do the following: –Property (copy from the numbered points in the book) –In your own words explain: how this property is related to hydrogen bonding and/or polarity (diagrams might help) why this property is important to living organisms (and specifically, in the human body)

Solubility The polar nature of water makes it a good solvent (many things dissolve in it) Substances that dissolve in a solvent are called solutes The polar nature of water makes it a good solvent (many things dissolve in it) Substances that dissolve in a solvent are called solutes

Ionic compounds are often soluble in water Positive and negative ions are attracted to different parts of the water molecule, and ionic compounds are pulled apart Ionic compounds are often soluble in water Positive and negative ions are attracted to different parts of the water molecule, and ionic compounds are pulled apart

Some molecular compounds, like sugar, dissolve in water because parts of the molecule are attracted to the water

non-polar molecules do not readily dissolve in water

Hydrophilic “water loving” Charged or polar molecules are hydrophilic and dissolve in water “water loving” Charged or polar molecules are hydrophilic and dissolve in water

Hydrophobic “water fearing” Non-polar molecules are hydrophobic and do not dissolve in water “water fearing” Non-polar molecules are hydrophobic and do not dissolve in water

Acids and Bases Acids release H + ions into water, so they contain more H + ions than OH - ions Bases release OH - ions into water, so they contain more OH - ions than H + ions Pure water is neutral - contains approximately equal numbers of H + and OH - ions Acids release H + ions into water, so they contain more H + ions than OH - ions Bases release OH - ions into water, so they contain more OH - ions than H + ions Pure water is neutral - contains approximately equal numbers of H + and OH - ions

Dissociation of water

pH Scale pH scale represents the concentrations of H+ ions in a solution Scale of 0 to 14 0 to <7 = acid (lower #, stronger acid) >7 to 14 = base or alkali (higher #, stronger base) 7 = neutral pH scale represents the concentrations of H+ ions in a solution Scale of 0 to 14 0 to <7 = acid (lower #, stronger acid) >7 to 14 = base or alkali (higher #, stronger base) 7 = neutral

Water has moles/L of H + (ph = 7) An acid with a pH of 4 has moles/L of H + A base with a pH of 10 has moles/L of H + Water has moles/L of H + (ph = 7) An acid with a pH of 4 has moles/L of H + A base with a pH of 10 has moles/L of H +

The pH scale is logarithmic, so the [H+] increases by 10x for each unit of pH ex. a pH of 5 has 10x as much H+ as a pH of 6 pH simulation Link The pH scale is logarithmic, so the [H+] increases by 10x for each unit of pH ex. a pH of 5 has 10x as much H+ as a pH of 6 pH simulation Link

pH in the body Cells require a certain pH range to live Too high or low pH denatures proteins and other molecules Enzymes that control biochemical reactions require the correct pH to function Cells require a certain pH range to live Too high or low pH denatures proteins and other molecules Enzymes that control biochemical reactions require the correct pH to function

Buffers Chemicals that prevent pH changes in solutions Take up extra H + or OH - ions Important in living organisms Maintain correct pH in cells and tissue fluids Ex. Buffers in blood maintain its optimal pH of ~7.4 Chemicals that prevent pH changes in solutions Take up extra H + or OH - ions Important in living organisms Maintain correct pH in cells and tissue fluids Ex. Buffers in blood maintain its optimal pH of ~7.4