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Page 1: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Water

Page 2: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Penny Lab

• Water has several important water properties that we will explore this week.

• Title your lab report “Penny Lab” and add it to your table of contents.

• First observation: How many drops of water can one penny hold?

Page 3: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Hypothesis

• Question: How does soap affect the amount of water one penny can hold?

• If…then…

Page 4: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Materials

• 2 pennies

• 2 dropper

• 1 beaker with water

• 1 beaker with soapy water

Page 5: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Experimental Design

• We are going to test if the amount of soap makes a difference

• Each group will have a different amount of soap in their soapy water

• We will compile class data and see what our results are

Page 6: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

White Board• How much soap did you have in your

soapy water?

• What was your hypothesis?

• What happened? Was your hypothesis supported or rejected?

• Draw a bar graph to compare your averages or tap water and soapy water.

• Answer one post lab question (teacher assigns)

Page 7: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Completing the Lab

• Draw your graph in your notebook.

• Look at class data. Describe if an increase in soapy water effected surface tension of water.

• Answer post lab analysis questions in your notebook. Write in complete sentences.

• Clean up your area

Page 8: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Water Race

• 3 drops of water• 1 toothpick• Who will be the

quickest at each table?

Page 9: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Challenge Round!

• Who will be our classroom champion??

Page 10: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Water

• What were some initial observations about your drop of water?

• What were some observations you made while you were in the race?

Page 11: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Properties of Water• Polar molecule• Cohesion and

adhesion• High specific heat• Density – greatest

at 4oC• Universal solvent of

life

Page 12: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Polarity of Water• Two hydrogen atoms form single

polar covalent bonds with an oxygen atom.

• This gives water more structure than other liquids

• Because oxygen is more electronegative, the region around oxygen has a partial negative charge.

• A water molecule is a polar molecule with opposite charges on each end of the molecule.

Draw a water molecule with charges.

Page 13: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

• Water has a variety of unusual properties because of attractions between these polar molecules.– The slightly negative regions of one molecule are

attracted to the slightly positive regions of nearby molecules

– They form a hydrogen bond.– Each water molecule

can form hydrogen bonds with up to four neighbors.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.1

Page 14: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

HYDROGEN BONDS• Hold water molecules

together

• Each water molecule can form a maximum of 4 hydrogen bonds

• The hydrogen bonds joining water molecules are weak– about 1/20th as strong as

covalent bonds.

• They form, break, and reform with great frequency

• Extraordinary Properties that are a result of hydrogen bonds.– Cohesive behavior

– Resists changes in temperature

– High heat of vaporization

– Expands when it freezes

– Versatile solvent

Page 15: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

• Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.– Water has a greater surface tension than most other

liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface.

– Water behaves as if covered by an invisible film.

– Some animals can stand, walk, or run on water without breaking the surface.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.3

Page 16: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Cohesion vs. Adhesion

Page 17: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Organisms Depend on Cohesion

• Cohesion is responsible for the transport of the water column in plants

• Cohesion among water molecules plays a key role in the transport of water against gravity in plants

• Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.

Hydrogen bonds hold the substance together, a phenomenon called cohesion

Page 18: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Exploring pH

• What do you already know?

Page 19: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Exploring pH

• What is pH measuring?

• What does the H stand for?

• Think of the water molecule

• If we take away an H+, what is left?

Page 20: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Data TableSolution pH [H+] pOH [OH-]

Tap water        

Distilled water       

Milk        

Salt        

Sugar        

PowerAde        

Soda        

Lemon Juice        

Bleach        

Corn Syrup        

Vinegar        

Glass cleaner        

Dish detergent       

Hand soap        

Page 21: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

White Board

• How can you organize these numbers?

• Draw a solution and put them in order

• What do you think is happening?

Page 22: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Soil at a high pH makes hydrangea flowers pink

Soil at a low pH makes hydrangea flowers blue

pH Key Concepts

Page 23: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

pH doesn’t just tell us if a solution is neutral, an acid or a base

It also tells us:

the concentration of H+ ions in the solution in moles/L

Water is neutral: [H+] = 1 x 10-7 M and pH = 7

pH and [H+]pH Key Concepts

Page 24: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

pH doesn’t just tell us if a solution is neutral, an acid or a base

It also tells us:

the concentration of H+ ions in the solution in moles/L

which is expressed as a power of 10

Water is neutral: [H+] = 1 x 10-7 M and pH = 7

pH and [H+]pH Key Concepts

Page 25: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Power of 10

A negative exponent means the number is less than 1

pH Key Concepts

Page 26: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Definition of pH: pH = –log[H+]

Water is neutral: [H+] = 1 x 10-7 M and pH = 7

Do not forget the “–” sign!

logarithm: in base 10, a number A derived from another number B such that 10B=A.

The number 7 is the

logarithm of 0.000 000 1

pH and [H+]pH Key Concepts

Page 27: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Dissociation of water:

H2O(l) H+(aq) + OH–(aq)

[H+] and [OH–] are related

pH for bases

[H+][OH-] = 1 x 10-14

Becomes:pH + pOH = 14

pH Key Concepts

Page 28: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Household chemical

Acid or base pH

ammonia base 11

bar soap base 10

baking soda base 8.5

soda water acid 4

vinegar acid 3

lemon juice acid 2

pH range

pH can be less than 0 for stronger acidsgreater than 14 for stronger bases

pH Key Concepts

Page 29: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Measuring pH

The color of red cabbage juice at different pH

You can’t measure pH by just looking at a solution, or measuring its density

or temperature, but you can measure pH indirectly by:

- performing a chemical reaction with a solution of known pH

- using a chemical that changes color at different pH values

(pH indicators)

pH Key Concepts

Page 30: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Measuring pH

You can’t measure pH by just looking at a solution, or measuring its density

or temperature, but you can measure pH indirectly by:

- performing a chemical reaction with a solution of known pH

- using a chemical that changes color at different pH values

(pH indicators)

pH Key Concepts

Page 31: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

You can’t measure pH by just looking at a solution, or measuring its density

or temperature, but you can measure pH indirectly by:

- performing a chemical reaction with a solution of known pH

- using a chemical that changes color at different pH values (pH indicators)

- measuring the electrical properties of the solution

Measuring pH

Acids and bases conduct electricity

pH and conductivity (flow of electricity) are related

a pH meter

pH Key Concepts

Page 32: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Most biochemical reactions involve solutes dissolved in water.

• There are two important quantitative proprieties of aqueous solutions.

– 1. Concentration

– 2. pH

Page 33: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Concentration of a Solution

• Molecular weight – sum of the weights of all atoms in a molecule (daltons)

• Mole – amount of a substance that has a mass in grams numerically equivalent to its molecular weight in daltons.

• Avogadro’s number – 6.02 X 1023

– A mole of one substance has the same number of molecules as a mole of any other substance.

Page 34: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

MolarityThe concentration of a material in solution is called its molarity.

A one molar solution has one mole of a substance dissolved in one liter of solvent, typically water.

Calculate a one molar solution of sucrose, C12H22O16.

C = 12 daltons

H = 1 dalton

O = 16 daltons

12 x12 = 144

1 x 22 = 22

16 x 11 = 176

342For a 2M solution?

For a .05 M solution?

For a .2 M solution?

Page 35: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

• Occasionally, a hydrogen atom shared by two water molecules shifts from one molecule to the other.– The hydrogen atom leaves its electron behind and is

transferred as a single proton - a hydrogen ion (H+).– The water molecule that lost a proton is now a

hydroxide ion (OH-).– The water

molecule with the extra proton is a hydronium ion (H3O+).

Dissociation of Water Molecules

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Unnumbered Fig. 3.47

Page 36: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

• A simpler way to view this process is that a water molecule dissociates into a hydrogen ion and a hydroxide ion:

– H2O <=> H+ + OH-

• This reaction is reversible.

• At equilibrium the concentration of water molecules greatly exceeds that of H+ and OH-.

Page 37: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

• In pure water only one water molecule in every 554 million is dissociated.

– At equilibrium, the concentration of H+ or OH- is 10-7M (25°C) .

Page 38: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Acids and Bases• An acid is a substance that

increases the hydrogen ion concentration in a solution.

• Any substance that reduces the hydrogen ion concentration in a solution is a base.– Some bases reduce H+ directly by

accepting hydrogen ions.

• Strong acids and bases completely

dissociate in water.

• Weak acids and bases dissociate only partially and reversibly.

Page 39: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

pH Scale• The pH scale in any aqueous solution :

– [ H+ ] [OH-] = 10-14

• Measures the degree of acidity (0 – 14)

• Most biologic fluids are in the pH range from 6 – 8

• Each pH unit represents a tenfold difference (scale is logarithmic)– A small change in pH actually indicates a

substantial change in H+ and OH- concentrations.

Page 40: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

ProblemHow much greater is the [ H+ ] in a solution with pH 2 than in a solution with pH 6?

Answer:

pH of 2 = [ H+ ] of 1.0 x 10-2 = 1/100 M

pH of 6 = [ H+ ] of 1.0 x 10-6 = 1/1,000,000 M

10,000 times greater

Page 41: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Buffers• A substance that eliminates large sudden

changes in pH.• Buffers help organisms maintain the pH of

body fluids within the narrow range necessary for life. – Are combinations of H+ acceptors and

donors forms in a solution of weak acids or bases

– Work by accepting H+ from solutions when they are in excess and by donating H+ when they have been depleted.

Page 42: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Acid Precipitation• Rain, snow or fog with more strongly acidic than pH of

5.6• West Virginia has recorded 1.5• East Tennessee reported 4.2 in 2000• Occurs when sulfur oxides and nitrogen oxides react

with water in the atmosphere– Lowers pH of soil which affects mineral solubility

– decline of forests– Lower pH of lakes and ponds – In the Western

Adirondack Mountains, there are lakes with a pH <5 that have no fish.

Page 43: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Salt Water vs. Fresh Water

• Boiling Point

• Freezing Point

• Gummy Bear Osmosis

Page 44: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Freezing Point

• What happens to salt water after 1 hour in the freezer?

• Independent variable?

• Dependent variable?

• Control?

• Hypothesis: If… then…

Page 45: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Gummy Bear Osmosis

• Read through handout

• Define roles for each group member and write them down

• Measurements and Lab set up

• Day 2 Friday

• Day 3 Monday

• Lab report will be due Tuesday beginning of class

Page 46: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Ice Cream Composition

Page 47: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Freezing Point

• What happened to salt water after 1 hour in the freezer?

• Was it what you expected?

• Analyze the results

• Exit Ticket: Draw a sketch of salt water molecules

Page 48: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Boiling Point

• What happens to salt water after 1 hour in the freezer?

• Independent variable?

• Dependent variable?

• Control?

Page 49: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Moderates Temperatures on Earth

• What is kinetic energy?• Heat?• Temperature?• Calorie?• What is the difference

in cal and Cal?• What is specific heat?

Celsius Scale at Sea Level

100oC Water boils

37oC Human body temperature

23oC Room temperature

0oC Water freezes

 

Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.

Page 50: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for:

1. Prevention of temperature fluctuations that are outside the range suitable for life.

2. Coastal areas having a mild climate

3. A stable marine environment

Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to

change its temperature by 1oC.

Page 51: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Evaporative Cooling• The cooling of a

surface occurs when the liquid evaporates

• This is responsible for:– Moderating earth’s

climate

– Stabilizes temperature in aquatic ecosystems

– Preventing organisms from overheating

Page 52: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Density of Water• Most dense at 4oC• Contracts until 4oC• Expands from 4oC to

0oC

The density of water:

1. Prevents water from freezing from the bottom up.

2. Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.

3. Makes transition between season less abrupt.

Page 53: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

– When water reaches 0oC, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners.

– As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state.

– Ice is about 10% less dense than water at 4oC.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.5

Page 54: Water. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table

Solvent for Life• Solution

– Solute– solvent

• Aqueous solution• Hydrophilic

– Ionic compounds dissolve in water

– Polar molecules (generally) are water soluble

• Hydrophobic– Nonpolar compounds