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Water, Mixtures, Acids, Bases , Ph and Indicators. Importance in Science and Impact on Living Things. Water That “polar” little molecule. Essential for Life (65-70% of our Mass) Universal Solvent (Most substances are Dissolved in or Transported by Water
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Water, Mixtures, Acids, Bases , Ph and Indicators • Importance in Science and Impact on Living Things
WaterThat “polar” little molecule • Essential for Life (65-70% of our Mass) • Universal Solvent (Most substances are Dissolved in or Transported by Water • Ability to Dissolve Substances is due to its Polar Nature (Opposite charges along the molecule)
More about Water Why are we studying water? All life occurs in water • inside & outside the cell
WATER a non-living moleculeESSENTIAL FOR LIFE Water is Polar (has a positive region and a negative Region) The Negative End (oxygen) of one water molecule Attracts the Positive End (Hydrogen) Of another water molecule Slightly Negative Oxygen Hydrogen Hydrogen Slightly positive Slightly positive
1. Chemistry of water • H2O molecules form H-bonds with each other • +H attracted to –O • creates a sticky molecule
Water is Cohesive • A force of attraction between molecules of the same substance is “Cohesion” • Cohesion, or the ability of molecules to “stick together" is because opposite charges attract each other • Water molecules attract other water molecules, forming HYDROGEN BONDS
Water is alsoAdhesive • Adhesionhappens when there is attraction between two different substances • Because Water is POLAR, it adheres to many other substances • Water is one of the Best Solvents because other molecules are Attracted to Water • Intermolecular Hydrogen Bonding accounts for water’s properties of Cohesion and Adhesion
Cohesive and Adhesive Properties in Action • Water moving up roots, forming droplets, creating surface tension
How does H2O get to top of trees? Transpiration is built on cohesion & adhesion Remember the videotape!
In Summary….. • Special properties of water 1. cohesion & adhesion • surface tension, capillary action 2. good solvent • many molecules dissolve in H2O • hydrophilic vs. hydrophobic 3. lower density as a solid • ice floats! 4. high specific heat • water stores heat 5. high heat of vaporization • heats & cools slowly Ice!I could use more ice!
2. Water is the solvent of life • Polarity makes H2O a good solvent • polar H2O molecules surround + & – ions • solvents dissolve solutes creating solutions
What dissolves in water? • Hydrophilic • substances have attraction to H2O • polar or non-polar?
What doesn’t dissolve in water? • Hydrophobic • substances that don’t have an attraction to H2O • polar or non-polar? Oh, lookhydrocarbons! fat (triglycerol)
3. The special case of ice • Most (all?) substances are more dense when they are solid, but not water… • Ice floats! • H bonds form a crystal And this hasmade all the difference!
Why is “ice floats” important? • Oceans & lakes don’t freeze solid • surface ice insulates water below • allowing life to survive the winter • if ice sank… • ponds, lakes & even oceans would freeze solid • in summer, only upper few inches would thaw • seasonal turnover of lakes • sinking cold H2O cycles nutrients in autumn
4. Specific heat • H2O resists changes in temperature • high specific heat • takes a lot to heat it up • takes a lot to cool it down • H2O moderates temperatures on Earth
5. Heat of vaporization Evaporative cooling Organisms rely on heat of vaporization to remove body heat
Compounds are atoms or ions joined by Chemical Bonds Combine in Fixed proportions and a definite structural arrangement Are changed physically and chemically Mixtures consist of two or more substances NOT chemically combined No definite proportions Each substance retains its original chemical and physical properties Compounds verses Mixtures
Homogeneous Mixtures(the same through out) • Solutions are generally Clear homogeneous mixtures • Consist of …. • Solvent (like Water) substance doing the dissolving • Solute (like Salt, Sugar) is the substance being dissolved
Dissolving • When a molecular substance Dissolves in a Liquid, the substance separates into its individual molecules • Sugar molecules spread throughout the water (going into solution)
When Ionic compounds Dissolve they also Dissociate • When Ionic compounds are dissolved, the ionic bonds holding them together are broken due to the attractive forces of the water molecule NaCl (table salt) dissociates To form Na+ and Cl- Ions
Ionization of water & pH • Water ionizes • H+ splits off from H2O, leaving OH– • if [H+]= [-OH], water is neutral • if [H+]> [-OH], water is acidic • if [H+]< [-OH],water is basic • pH scale • how acid or basic solution is • 1 7 14 H2O H+ + OH–
H+ Ion Concentration Examples of Solutions pH 100 0 Hydrochloric acid 10–1 1 10–2 2 Stomach acid, Lemon juice Vinegar, cola, beer 10–3 3 Tomatoes 10–4 4 10–5 5 Black coffee, Rainwater 10–6 6 Urine, Saliva 7 Pure water, Blood 10–7 Seawater 8 10–8 Baking soda 10–9 9 Great Salt Lake 10–10 10 10–11 Household ammonia 11 10–12 12 Household bleach 10–13 13 Oven cleaner 10–14 14 Sodium hydroxide pH Scale tenfold changein H+ ions pH1 pH2 10-1 10-2 10 times less H+ pH8 pH7 10-8 10-7 10 times more H+ pH10 pH8 10-10 10-8 100 times more H+
What is Ph and What can it tell us? • Ph is a way of representing the Hydrogen ion [H+] concentration of an acidic or basic solution • Defined as the –log of [H+] • In other words, the greater the number of H+produced by a dissolved substance, the smaller the Ph value • Ph can tell us if something is an acid or a base AND its strength!
Dissociation producesAcids and Bases Acids produce excess H+ ions Bases produce excess OH- ions
Ph Scale • Ph scale goes from 0-14 The stronger the acid the lower the ph value Acids have the highest concentrations of H+ The stronger the Base the higher the ph value Bases have the lowest concentrations of H+ High [OH-]
Produce Excess Hydrogen ions (H+ ) when they dissociate in water Ph values less than 7 Taste Sour Corrode metals Produce Excess Hydroxide ions(OH-) when they dissociate in water Ph values greater than 7 Taste Bitter Emulsify Fats (droplets) Slippery (soapy) Acids VersesBases
Citric Acid (lemons oranges, limes) Acetic Acid (vinegar) Carbonic Acid (soda) Hydrochloric Acid (HCl) stomach Sulfuric and Nitric Acids (acid rain) Sodium Hydroxide (NaOH) Lye, Draino Sodium Bicarbonate (Baking Soda) Ammonia (NH3) cleaners Common Acids and Bases
Indicators “indicate” if something is an acid or a base • An indicator is a substance that changes color when the pH goes above or below a certain pH range. • So, indicators can tell us when any given substance is either more acidic or more basic by simply Changing color
Examples of Indicators • Litmus turns Red in an acid; but will change Blue in a Base • Methyl Orange changes from Yellow to Orange in acids (pH <3) • Phenolphthalein changes from colorless/clear to Pink in bases (pH >8)
Neutralization Results when an Acid is Mixed with a Base • Neutralization means that the pH is no longer acidic or basic; it reaches a pH of 7 (neutral) • NaOH + HCl -------------H2O + NaCl • The H+ of the acid combines with OH- of the base to produce water and salt Neutralization Reaction Strong Acid Water Salt Strong Base pH =12 pH = 2 pH = 7
Buffers are chemicals that neutralize excess acids or bases • Buffers are compounds that act differently depending on “what they are mixed with” • When mixed with a Strong Acid; a buffer behaves like a weak base -- neutralizing the Acid • When mixed with a Strong Base; a buffer acts like a weak acid ----- neutralizing the Base • TUMS, Milk of Magnesia are examples of buffers that neutralize excess stomach acid
9 8 7 6 Buffering range 5 pH 4 3 2 1 0 0 1 2 3 4 5 Amount of base added Buffers & cellular regulation • pH of cells must be kept ~7 • pH affects shape of molecules • shape of molecules affect function • pH affects cellular function • Control pH by buffers • reservoir of H+ • donate H+ when [H+] falls • absorb H+ when [H+] rises
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