Chemistry of Life Properties of Water Chapter 3 Pre Assessment 1.What causes water to travel up the...
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Transcript of Chemistry of Life Properties of Water Chapter 3 Pre Assessment 1.What causes water to travel up the...
Pre Assessment
1. What causes water to travel up the roots of a plant?
2. What allows bugs to walk on top of water?3. Why does ice float in water if they are both
the same compounds?4. Draw a pH scale and label-acids, bases, and
neutral substances. 5. Why is water known as the universal solvent?
WaterWhy are we studying water?Why are we studying water?
All life occurs in water inside & outside the cell
All life occurs in water inside & outside the cell
Makes up 70-90% of all living things.75% of the earth’s surface is covered with water
Makes up 70-90% of all living things.75% of the earth’s surface is covered with water
Chemistry of water• H2O molecules form H-bonds
with each other– +H attracted to –O– creates a
sticky molecule
Water Molecules
• Hydrogen bonds~ relatively weak bonds last only 1/billionth of a second in liquid water, but are constantly broken and reformed.
• Polar —shared electrons of the covalent bonds spend more time around the oxygen atom than they do around the hydrogen nuclei.
• water animation
Elixir of Life• 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!
1. Cohesion & Adhesion
Walking on water
• Cohesion– H bonding between H2O molecules– water is “sticky”
• surface tension• drinking straw
• Adhesion– H bonding between H2O & other substances
• capillary action• meniscus• water climbs up
paper towel or cloth
Water molecules are cohesive and adhesive.
Cohesion— water molecules cling to other water molecules because of hydrogen bonding.
Adhesion— water molecules adhere to polar surfaces because they have positive and negative poles (polarity).
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– Philic=affinity – polar or non-polar?
What doesn’t dissolve in water?• Hydrophobic
– substances that have an attraction to H2O
– Phobic= fear– polar or non-polar?
fat (triglycerol)
Oh, lookhydrocarbons!
3. The special case of ice• Most (all?) substances are more dense when
they are solid, butnot 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
Water has a high heat capacity.
specific heat—the amount of heat a given amount of a substance requires for an increase in temperature.Examples: water = 1 ethyl alcohol = 0.6
sucrose = 0.3 liquid ammonia = 1.23calorie —the amount of heat that will raise the temperature of 1 g (1 mL or 1 cc) of water 1o Celsius.
5. Heat of vaporizationEvaporative cooling
Organisms rely on heat of vaporization to remove body heat
Water has a high heat of vaporization.
• It requires 540 calories of heat energy to convert 1 g of the hottest water to a gas.
– This is 60 X as much as for ether and 2X as much as for ammonia.
Why does water have this high heat of vaporization?Hydrogen bonds must be broken before water boils and water molecules vaporize.
Why does water have a high heat capacity?The many hydrogen bonds that link water molecules help it to absorb heat without a great change in temperature.
What are the consequences of this property to living things?Because the temperature of water rises and falls slowly, organisms are better able to maintain their normal internal temperatures and are protected from rapid temperature changes (Homeostasis)
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–H2O H+ + OH–
pH Scale10–1
H+ IonConcentration
Examples of Solutions
Stomach acid, Lemon juice1
pH100 Hydrochloric acid0
10–2 2
10–3 Vinegar, cola, beer3
10–4 Tomatoes4
10–5 Black coffee, Rainwater5
10–6 Urine, Saliva6
10–7 Pure water, Blood7
10–8 Seawater8
10–9 Baking soda9
10–10 Great Salt Lake10
10–11 Household ammonia11
10–12 Household bleach12
10–13 Oven cleaner13
10–14 Sodium hydroxide14
tenfold changein H+ ions
pH1 pH210-1 10-2
10 times less H+
pH8 pH710-8 10-7
10 times more H+
pH10 pH810-10 10-8
100 times more H+
Check Point
Acid –Base-or Neutral???1. pH of 8.42. A solution with more H+ ions the OH- ions3. A solution with an equal amount of H+ ions
and OH- ions4. A pH of 75. A base and an acid combined
1001
2
3
45
6
7
89
3Amount of base added
Bufferingrange
4 52
pH
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
Solutions
• Solvent— the substance that does the dissolving
• Solute— the substance that is dissolved
• Solution— a homogeneous mixture that will not separate upon standing
Aqueous Solutions• Mole— the number of grams of a substance that equals
its molecular weight in daltons.Example: sucrose, C12H22O11
12 carbons = 14422 hydrogens =2211 oxygens = 176
One mole is equal to 342 grams. To make a 0.5 M solution, add water to 171 grams to make 1 Liter of solution.
Post Assesment
1. Name a benefit of cohesion and adhesion to animals and plants.
2. Name a solution-identify the solute and the solvent.
3. Name an example of a neutral substance in our bodies.
4. Name an a solution in our bodies that is acidic? How does it get neutralized?
5. How many times more acidic is a solution with a pH of 1 than a solution with a pH of 2?