new aim: what is so important about water? chapter 3 – water and the fitness of the environment

NEW AIM: What is so important about water?

Chapter 3 – Water and the fitness of the environment

O

HH

AIM: What is so important about water?Chapter 2 - The Chemical Basis of Life

Water has a bent geometry because the lone pair electrons in the valence shell of oxygen repel the electrons in ths O-H bonds giving it a “v” shape.

Lone pair electrons

AIM: What is so important about water?Chapter 3 – Water and the fitness of the environment

Chapter 2 - The Chemical Basis of Life AIM: What is so important about water?

Electronegativity: An elements attraction (affinity for) electrons. Remember that affinity for electrons depends on the

charge of the nucleus AND the distance the electrons are from the nucleus. The further they are, the weaker the EM force. The fewer the protons in the nucleus, the weaker the EM force.



Electronegativity: An elements attraction (affinity for) electrons. Therefore, as you move left to right on the periodic

table, the electronegativity increases since the nucleus is getting larger, but the distance from the nucleus is staying the same.



Electronegativity: An elements attraction (affinity for) electrons.

As you move up a group, the electronegativity increases. This is because the valence shell electrons get closer to the nucleus (they have fewer shells/orbitals) even though the nuclei have fewer protons.

Fluorine has the highest electronegativity. Why not neon or helium?Neon/Helium have a full valence shell and therefore are already stable all by themselves and will not attract electrons to be stable.In biology, we will focus on elements with high electronegativity like oxygen and nitrogen.


O

HH

Chapter 2 - The Chemical Basis of Life AIM: What is so important about water?AIM: What is so important about water?Chapter 3 – Water and the fitness of the environment


Oxygen has a higher electronegativity than hydrogen and therefore the shared electrons will be more likely to be around oxygen than hydrogen giving oxygen a partial negative charge and hydrogen a partial positive charge.


Chapter 2 - The Chemical Basis of Life

PolarNon-polar

vs

covalent bonds

AIM: What is so important about water?

A polar covalent bond results when two elements of different electronegativity form a covalent bond resulting in an unequal sharing of electrons. One becomes partially negative and the other becomes partially positive. Ex. O-H : the O is partially neg. and the H is partially positive since oxygen has a higher electronegativity compare to hydrogen.



PolarNon-polar

vs

covalent bonds


They are called “polar” because they have opposite ends (one end is partial neg. and the other is partial pos.). The Earth has poles or is polar – north pole and south pole. Bipolar personality disorder – sometimes manic and sometimes depressed. Magnets are polar – north pole and south pole.



PolarNon-polar

vs

covalent bonds


A non-polar covalent bond results when two elements of similar electronegativity form a covalent bond resulting in an equal sharing of electrons. Both ends of the bond are neutral. Ex. C-C or C-H bonds.



Non-Polar Covalent Bonds Polar Covalent Bonds (δ- on left, δ+ on right)

Any covalent bond between two of the same elements:O-OC-CH-HEtc…

O-HN-HS-HO-CO=CEtc…

C-H

Why is the C-H covalent bond considered non-polar while the O-H and N-H bonds are polar?Carbon has 6 protons, while hydrogen has 1 proton. Therefore, in terms of nuclei, Carbon wins, but hydrogen only has one shell and carbon has two. Therefore, the electrons are much closer to hydrogen than to carbon. The closer distance balances the smaller number of protons in the nucleus resulting in carbon and hydrogen having a similar electronegativity.



Which bonds are Polar and which are non-polar?

AIM: What is so important about water?AIM: What is so important about water?Chapter 3 – Water and the fitness of the environment


PolarNon-polar

and

Molecules


Most molecules are a mix of polar and non-polar covalent bonds. The ratio will determine how polar/non-polar the molecules will be.



How would multiple water molecules interact with each other?



The partially negative oxygens will be attracted to the partially positive hydrogens forming what is called a hydrogen bond.


http://www.visionlearning.com/library/module_viewer.php?mid=57


Hydrogenbonding


A hydrogen bond (H-bond) is a weak bond (weaker than an ionic or covalent bond) formed between two partially charged atoms, one of which is a hydrogen.

Each water can make up to four H-bonds, one to each hydrogen and one to each of the lone pairs. In liquid water, the H-bonds are constantly being formed and broken.


http://www.visionlearning.com/library/module_viewer.php?mid=57


How would multiple water molecules interact with a non-polar molecule?



Water molecules will not interact with non-polar molecules because non-polar molecules have no charge to “stick” to. Water molecules interact with other charged substances.



The molecule on the right is mostly non-polar (almost all C-C and C-H bonds). This region is known as the hydrophobic (water-fearing) end since it will not interact with water. The other end has some polar covalent bonds (C=O, O-H, C-O) making the tip of this molecule hydrophilic (water-loving) because water can H-bond to this part.



Compare and contrastcovalent, ionic and hydrogen bonds


Covalent bonds share electrons between two atoms to satisify the valence shells (C-C).

H-bonds are weaker than ionic and covalent bonds since only partial charges hold the two substances together.

Bond Strengths:

Ionic bonds result from donating elecrons from one atom to another resulting in a full and opposite charge in each atom, which causes them to attract each other (Na+ Cl-).Hydrogen bonds occur between partially charged atoms, one of which is typically a hydrogen. They result because of unequal sharing of electrons in covalent bonds due to differences in electronegativity.



What about Van der Waals Interactions (London dispersion)?


Even non-polar molecules may have some positively and negatively charged region briefly and therefore can very weakly bind to each other…

Figure 1. Two non-polar molecules (say H2) come into close proximity

Figure 2. By chance, the position of the electrons around one of the molecules (the one of the left) are more on one side of the molecule than the other causing one side to be ever so slightly negative and the other side to be ever so slightly positive.

Figure 3. This will then induce a dipole in the neighboring molecule as the neighboring molecule’s electrons will be attracted to the slightly positive region of the first molecule resulting again in an ever so slightly negative side and an ever so slightly positive side. Of course, the negative and positive will form a very weak interaction.

Dipole = two poles, or a positive side and a negative side. For example, a carbonyl (C=O) is a dipole as the carbon is partially positive and the oxygen partially negative.



Weak interactions add up…


Think about velcro.

Velcro consists of on side having numerous tiny hooks and the other having “fuzz” for each hook to wrap around. A single hook/fuzz interaction is extremely weak…

Where do we see such additive affects of weak bonds in biological systems?

However, hundreds of thousands of such interactions are additive and become important in the case of velcro jumping.





The two strands of a DNA molecule are held together tightly by the additive affect of many, many weak Hydrogen Bonds


Plasma membrane are stabilized by the additive affect of Van der Waals interactions between non-polar fatty acid tails of phospholipids.






Geckos have been shown to walk up walls using countless numbers of Van der Waals interactions…



How is a water molecule held together?


A water molecule itself is held together by covalent bonds.



How are water molecules held together?


Water molecules are held to each other in liquid and solid (ice) by hydrogen bonds.



Structure (Geometry/Shape and Polarity/charge)


What determines the properties of water?

All of water’s properties are the product of its molecular structure/charge. All matter, including yourself, cannot be properly understood unless you understand the underlying molecular structures.



Water is the only substance in nature to exist in the three common states of matter – liquid, solid, gas



This image demonstrates the cohesive (sticks to itself by H-bonds) properties of water. This is what holds it in droplet form. The leaf us covered with non-polar molecules, which is why the water will not stick to it (there is no charge to interact with)



Cohesion gives water surface tension as the water molecules H-bond to each other on the surface forming a very delicate sheet that insects like this water strider can actually walk on without breaking.


How do plants get water/minerals from the roots to the leaves against the force of gravity without a mechanical pump like out heart?

Chapters 32: Plant Nutrition and Transport

Fig. 32.3

Transpiration

- loss of water from leaves (stomata) pull xylem sap (water/minerals) upward

a. cohesion (water hydrogen-bonding to other waters): makes the xylem sap like a continuous string of “water beads”

b. Adhesion (water hydrogen-bonding to other molecules): sticks to cellulose walls of xylem cells

- Two properties of water that make this possible:


Recall that the xylem is a network of dead cells involved in transporting water and minerals up from the soil.



Fig. 32.3

- water molecule at end of chain in leaf is heated by solar energy- This molecule is “knocked” out of the stomate and evaporates- As it does this, it pulls on the neighboring waters that it hydrogen bonds to (cohesion), the neighbors pull on their neighbors and so on all the way to the roots

(Without the suns KE, the water in the leaf would remain stuck to its neighbors - no pulling force, no transpiration)



Transpiration



Fig. 32.3

- What about adhesion?- adhesion counters downward pull of gravity by “grabbing” (hydrogen bonding to) walls of xylem- holds water in xylem when transpiration is not occurring (at night)



Transpiration



HeatvsTemperatureAIM: What is so important about water?

Heat is referring to molecular motion. The “hotter” something is, the quicker the molecules are moving/vibrating. If something hot touches you like a hot iron, the rapidly vibrating molecules with crash into your skin causing your skin molecules to vibrate rapidly resulting in damage to the structure of your molecules/cells. It is the measure of the total amount of KE due to molecular motion in a body of matter.

Temperature is the average motion of all the molecules in a substance. For example, in a glass of water that is 98.6 F (body temperature) the molecules have a certain average speed (about 700 meters per second). However, some will be moving faster than that and some will be moving slower. The temperature just tells us the average motion or KE of all the molecules.



What is specific heat?The amount of “energy” (collisions) it takes to heat up 1 gram of the substance by 1 degree Celcius. It takes a lot of energy to do this to water: 1 calorie (cal) of energy to be exact).

Therefore the specific heat of water =

1 cal/g/°C

1 cal = 4.184 Joules (J)

Another way to say this is specific heat is a measure of how well as substance resists a change in temperature.



Water, because of it H-bonding (cohesive nature) has a very high specific heat relative to other molecules. This is because when molecules collide with the water molecules, it is difficult to get them vibrating since those waters are all sticking to each other. The H-bonds need to be broken. Think about the analogy in class where it is easy to push a single student and get them moving fast, but if you all hold hands, it becomes more difficult as I would need to break those bonds.

Conclusion: water can absorb a great deal of energy without its temperature rising too greatly and vice versa, which is why it takes quite a bit of time to boil water on your stove relative to boiling another liquid like ethanol whose specific heat is 0.6 cal/g/°C.



Because of the high specific heat, the temperature of coastal regions, especially islands, are regulated. During the summer, the water absorbs a lot of the sunlight’s energy and only heats up minimally resulting in cooler air temperatures. During winter, the water releases the energy warming the air keeping the winters warmer.



Great Ocean Conveyor Belt delivering heat to the Northern Hemisphere….



The Great Ocean Conveyor Belt, as you should have learned in Earth Science, is a massive global current that carries energy from the sunlight at the equator, which is stored as heat in the water, up to the North keeping North America and Europe much warmer than it would be otherwise. One of the many fears of global warming is a disruption of this current resulting in colder temperatures in the North and the next Ice Age.



Water helps modulate our body temperature as well. Just like water regulates the temperatures of land masses, it also helps organisms to resist temperature changes. Once again, the high specific heat of water means that is takes a great deal of energy to heat it up. Therefore, we can burn a lot of glucose and fat to move around, but our bodies will not quickly overheat as a result.



Evaporative COOL

ING


Heat of Vaporization

Amount of energy (heat) required to turn a substance from a liquid to a gas.

What can you predict about water’s heat of vaporization and why do you predict this?

It is relatively high because once again, the waters are all H-bonded to each other, which must be broken in order to evaporate.



Evaporative COOL

ING


We also use water to cool ourselves down when we do eventually start to overheat to maintain a homeostatic level of 98.6 F. How does this work?

When we overheat, we sweat. The sweat (water, salt and a bit of urea) sits on our skin. The molecules of your skin, which are moving too quickly (because you are overheating) will bump into the water, The result is your molecules moving slower and the water speeding up (energy transfer). Some of the water will move fast enough to jump off of your body (evaporate), carrying the kinetic energy away with it thereby cooling you down.


The solid phase of water (ice) floats

Chapter 2 - The Chemical Basis of Life AIM: What is so important about water?AIM: What is so important about water?Chapter 3 – Water and the fitness of the environment


Why does ice float and does this matter in terms of life on this planet?

Ice floats because it is less dense than liquid water. What does that mean?It means that the water molecules take up more

space/volume when water freezes compared to when it is a liquid (density is mass/volume). The mass is the same, but the volume is greater. Why is the volume greater?



The volume is greater because when water is cooled down (the molecules slow down) each water molecule will eventually move slow enough to make the maximum (4) hydrogen bonds with other waters forming a crystal of water (ice). The crystal has large spaces in it that liquid water doesn’t have making it less dense. In liquid water, the water molecules are moving quickly and H-bonds are being made and broken constantly and those large spaces found in ice are filled in making liquid water more dense.



Great, but who cares if ice floats?

Arguably, life would not exist. If ice were more dense, as it forms in winter it would sink making the bottoms of lakes/oceans/etc… colder and eventually a build up of ice would occur. This ice is deep enough that even in the summer it would not melt as it would be insulated by the upper layer of water. The ice would build winter after winter until the oceans/lake would be completely frozen. The great ocean conveyor belt certainly would not exist and the Earth would be a snowball…



Great, but who cares if ice floats?

Therefore, ice is a barrier or insulator against the cold air above and protects waterways from freezing over allowing life to persist.

euphausid shrimp below arctic ice



The Universal Solvent


(Solution, solvent, solute)

Solvent – that which is dissolving the soluteSolute – that which is being dissolvedSolution – the result of a solute being dissolved in a solvent, a homogeneous mixture



The Universal Solvent


(Solution, solvent, solute)Water is referred to as the universal solvent because it can dissolve a huge number of different substances; all of which are hydrophilic (contain many polar covalent bonds) and or charged.Ex. Water can dissolve salts, proteins, carbohydrates, DNA, RNA, vitamins, minerals, phosphate, nitrate, and the list goes on and on… All of these molecules are hydrophilic.



What does it mean to dissolve?



This is a figure showing water dissolving a crystal of sodium chloride, which it can easily do because the sodium is positively charged and the chloride is negatively charged.

Hydration shell“Cage” of water molecules surrounding each dissolved substance



Like Dissolves LikeWater is polar and therefore will dissolve other polar/charged substances because it can stick to and surround them in solution.Water cannot dissolve olive oil, because olive oil is mostly non-polar and therefore it has no charge to interact with and is termed non-polar. The water will stick to other water molecules excluding the oil, which is why the oil floats on the water.However, olive oil can dissolve in other non-polar substances like vegetable oil. They are both non-polar and therefore neither will stick to the other (ignoring Van der Waals), but nothing prevents them from mixing together.



All of the properties we have discussed thus far trace back to…

Cohesion

Moderation of Temperature

Ice Floats

Adhesion

Universal Solvent

…charge (H-bonding) and geometry:



Which can ultimately be traced back to the number of protons (reductionist)…Remember that all of these properties stem from the fact the water makes hydrogen bonds with 4 other waters due to its geometry, which is the result of its electron arrangements, and its charge due to oxygen being more electronegative than hydrogen because it has 8 protons vs. hydrogen’s one proton, and the protons also determine the electron arrangement. It all goes back to the number of protons!!!!!


NEW AIM: pH?

Concentration

Chapter 3 – Water and the fitness of the environment

Chapter 2 - The Chemical Basis of Life AIM: pH?

Which solution has a higher concentration of sodium?

1 liter

Aqueous Na+Cl- solutions:

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+Na+

**“Aqueous” tells you the solvent is water.The solution on the left as the concentration is 5 Na+/L compared to the one on the right at 4 Na+/L.



1 liter

500 ml


The solution on the right as the concentration is 8 Na+/L compared to the one on the right at 5 Na+/L.


Which solution has a higher concentration of water?

1 liter

500 ml


If the solution on the right has more Na+ per unit volume then there must be less water per unit volume. Therefore the solution on the left has a higher concentration of water.



1 liter

500 ml


The concentrations are equal in this case at 8Na+/L.


Which solution has a higher concentration of water?

1 liter

500 ml


Again, they are equal.


If there were 6.02x1023 sodium atoms, what would the concentration be?

1 liter

Molarity

1 mol / L or…1 Molar (M)6.02x1023 sodiums/L =


[ ] = concentration

[glucose] = concentration of

glucose


Molarity (M)If I have a 10M glucose

solution, how many molecules of glucose would I have in 200ml ?There would be 10 moles (10 x 6.023x1023) of glucose in 1 L of solution. I took

200ml or 1/5th of a liter. Therefore, 200ml would have 2 moles of glucose or 2 x 6.023x1023 glucose molecules.


Potassium has


Molarity (M)Explain how you would

make 1L of a 300mM KCl solution.1. Determine the molecular weight (molecular mass) of KCl…

Atomic mass of K = 39.0983 daAtomic mass of Cl = 35.453 da

Molecular weight (m.w.) of KCl = 74.55 daWhich means what?

It means that 74.55g of KCl will be 1 mol of KCl compound….why? Explain.



make 1L of a 300mM KCl solution.It means that 74.55g of KCl will be 1 mol of KCl compound….why? Explain.

1. Remember that 1 mol of protons/neutrons = 1g

2. A single KCl on average has 74.55 protons/neutrons.

3. If I have 1 mol of KCl then I have 1 mol of 74.55 protons/neutrons or 6.023x1023 x 74.55 protons and neutrons.

4. Since 6.023x1023 x 1proton or neutron = 1g, then 6.023x1023 (1 mol) of 74.55 protons/neutrons = 74.55g



make 1L of a 300mM KCl solution.1. Determine the molecular weight (molecular mass) of KCl = 74.55

da telling us that there are 74.55 g/mol.2. Weigh out the necessary amount. You want to make a 300mM (300 milliMolar) solution = 0.3M solution = 0.3mol/L

Therefore you want to weigh out 0.3 moles

74.55g

1 mol=

X g

0.3 molX = 22.4g

0.3 mol = 22.4g



make 1L of a 300mM KCl solution.1. Determine the molecular weight (molecular mass) of KCl = 74.55

da telling us that there are 74.55 g/mol.2. Weigh out the necessary amount. 3. Add 22.4g to 900ml of water and stir 4. Bring volume up to 1 Liter



make 700ml of a 250mM NaCl solution.



make 250ml of a 200mM NaCl, 20mM Hepes solution at pH 6.8.

Hepes

Molecular mass (weight; m.w.) = mass of the molecule = 238.3 amu (daltons) for Hepes


H2

O


H2O H+

+ OH-

The oxygen atom is more electronegative than the hydrogens and pulls the shared electrons away from them, which can cause one of the hydrogens (a proton) to fall off. This happens to a small number of water molecules in any aqueous solution.

Hydrogen ion(aka… a proton)

Hydroxide ion

Because a small fraction of water (1 in a billion molecules) in an aqueous solution dissociates:

What is pH, why does such a value exist?


H2O H+

+ OH-

Hydrogen ion(aka… a proton)

Hydroxide ion

Although it appears that the hydrogen ion is now just diffusing around in solution, in actuality, what happens to it?

It will transfer from one water to another to form H3O+.


H2O H+

+ OH-

What is pH?

pH stands for potential hydrogen and is a measure of the concentration of hydrogen ions (protons) in an aqueous solution.

proton Hydroxide ion


H2O H+ +

OH-pH is measured on a

logarithmic scale from 0 to 14. The higher the H+ (free proton) concentration, the lower the pH


Acidic, Basic and neutral solutions


Acidic solutionBasic solution

One whose pH is below 7

One whose pH is above 7

Neutral solution

One whose pH is 7


What do these pH values mean in terms of actual [H+] values??

(H+ concentrations)

Chapter 2 - The Chemical Basis of Life AIM: pH? [H+] (M)

100 = 1M

10-1 = 1/10 = 0.1M

10-2 = 1/100 = 0.01M

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10-11

10-12

10-13

10-14

pH = -log [H+]

pH value

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14


Logarithms (logs)The log of a number is simply

how many powers of 10 you can pull out of that number.

Ex. log 1000= 3 because you can pull three powers of 10 out of 1000 (10 x 10 x 10) or 103 = 1000


Logarithms (logs)Ex. Log 100,000= 5 because you can

pull out 5 powers of 10 from 100,000 or 105 = 100,000.


Logarithmslog 102= log 100 =

log 103= log 1000 =

log 104= log 10,000 =

log 105=

log 106=

log 10-1= log .1 =

log 10-2=

log 10-3=

log 10-4=

23

4

5

6

-1-2

-3

-4


LogarithmsThen if you take the negative

log…The signs switch

-log 102=

-log 103=

-log 104=

-log 105=

-log 106=

-log 10-1=

-log 10-2=

-log 10-3=

-log 10-4=

-2

-3

-4

-5

-6

1

2

3

4


H2O H+

+ OH-

If you have pure water:

[H+] = 10-7 M

(concentration of “free” protons)[OH-] =



[H+] = 10-7 M

pH = -log [H+]

pH = -log [10-7M]pH = 7



[H+] = 10-7 M

pH = -log [H+]

pH = -log [10-7M]pH = 7 What if the

[H+] is 10X higher?


[H+] = 10-6 M

pH = -log [H+]

pH = -log [10-7M]pH = 7

pH = -log [H+]

x = -log [10-6M]pH = 6

[H+] = 10-7 M Increase 10 X


[H+] = 10-6 M

pH = -log [H+]

pH = -log [10-7M]pH = 7

pH = -log [H+]

x = -log [10-6M]pH = 6

[H+] = 10-7 M Increase 10 X

1. As [H+] goes up, pH goes DOWN

3. A change in 1 pH corresponds to a 10-fold change in [H+]2. As [H+] goes down, pH goes UP


1. What does the pH value tell us about the solution? 2. What happens to the pH as the [H+] increases? 3. If the pH of a solution is increased by three pH units, how has the [H+] changed?

The H+ (free proton) concentration [H+]

decreases

1000x lower [H+]


How many times more acidic is lemon juice than urine? 10,000X more acidic


How many times more basic is milk of magnesia (pH 11) compared to seawater (pH 8)? 1000X more basic


Acid

Basevs


AcidA substance that when added to a solution will cause the pH to decreaseEx. HCl (hydrochloric acid)HCl -> H+ + Cl-

Chlorine is highly electronegative relative to hydrogen and pull the shared electrons away causing the H+ to fall off.


BaseA substance that when added to a solution will cause the pH to increase (decrease the H+ concentration).

Ex) NaOH (sodium hydroxide)

NaOH Na+ + OH-

The OH- will then grab H+ in the solution and thereby lower the H+ concentration.

thenOH- + H+ H2O


1. If you add acid to a solution, is that solution acidic or basic?

2. Calculate the pH of a solution with an [H+] of 10-

2M.

You can’t know from this information. If you add acid to a solution with a pH of 11, you might change it to a pH of 10 (stays basic). If you change it to 6 then it will be acidic, but you need to know the final pH. Acids and Bases just raise and lower pH, they say nothing about the solution being acidic or basic.pH = -log[H+]

pH = -log[10-2]pH = 2

the pH of a solution

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?

How can one determine ?

RED LITMUS PAPER

Turns Blue in Basic


pH paper Indicators:

Aqueous solution applied here

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?Litmus is a water soluble mixture of different dyes extracted from lichens (composite organism consisting of a fungal/algae symbiotic relationship) and applied to paper.

Lichen growing on a tree

BLUE LITMUS PAPER

Turns reD in aciDic



Aqueous solution applied here



Hydrion paper



Hydrion paper contains a mixture of dyes that will turn various colors giving a more precise and quantitative (quantitative – means you can get numerical data) pH measurement .


pH paper Indicators:1. Red litmus

paper2. Blue litmus paper3. Hydrion paper


pH liquid Indicators:Liquid indicators can be

added to a sample taken from an aqueous solution. The color change of the indicator will reveal the pH.

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?pH liquid Indicators:

1. Phenolphthalein

Phenolphthalein will turn pink if the pH is above 8. If the pH is below 8, no color change is observed.


COLORLESS

PINK

The structure of the phenolphthalein molecule changes in different pH values. Above pH 8, it has a structure that reflects pink. Below 8 the structure changes and does not absorb light. Structure determines function!!

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?pH liquid Indicators:2. Bromothymol Blue

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?pH liquid Indicators:

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?pH liquid Indicators:Above pH 7 – blue

Below pH 6 – yellow

Between 6 and 7 - green

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?pH liquid Indicators:3. Methyl Orange


A pH liquid indicator for every occasion


How can I use these indicators to determine the pH of an unknown solution?

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?Use the following data and determine the pH of Dr. T’s magical elixir:

Alizarin yellow R: yellowThymol Blue(base range): yellowBromoresol green: yellowBromphenol blue: purpleThymol blue (acid range): ?

Indicator Used resultant color


Alizarin yellow R: yellow

Thymol Blue(base range): yellow

Bromoresol green: yellow

Bromphenol blue: purple

Thymol blue (acid range): ?

Chapter 2 - The Chemical Basis of Life AIM: How does one determine the pH of a solution?Use the following data and determine the pH of Dr. T’s magical elixir:

Alizarin yellow R: yellowThymol Blue(base range): yellowBromoresol green: yellowBromphenol blue: purpleThymol blue (acid range): ?

Indicator Used resultant color

Answer: ~pH 4

Answer: yellow


BuffersA buffer is a chemical (a weak acid or weak base) that when added to an aqueous solution will allow the solution to resist changes in pH.


BuffersExample - Let’s say you have carbonic acid in an aqueous solution:

H2CO3Carbonic acid(H+

donor)

HCO3- +

H+Base(H+ acceptor)

Response to rise in pH

Response to drop in pH

Le Chatelier's Principle states:

If I add acid (H+) to this solution in the form of HCl, I should push the reaction to the left as the H+ will combine with HCO3-. The HCO3- is acting like a sponge and absorbing the H+ that I add thereby preventing a pH change.

What happens if we add an acid like HCl to this solution?


BuffersExample - Let’s say you have carbonic acid in an aqueous solution:

H2CO3Carbonic acid(H+

donor)

HCO3- +

H+Base(H+ acceptor)

Response to rise in pH

Response to drop in pH

Le Chatelier's Principle states:

Likewise, if I add a base like OH-, it will combine with H+. Since I am removing H+, I will push the reaction to the right and H+ will be generated preventing a pH shift.

Why can’t a strong acid like HCl act as a base?

What if we add a base like NaOH?


Buffers Useful pH Range pKa

MES 5.5–6.7 6.16 6.10 5.97 M8250 M2933 M5287Bis-Tris 5.8–7.2 n/a 6.50 6.36 B9754 B4429 B7535ADA 6.0–7.2 6.65 6.59 6.46 A9883 n/a A8074aces 6.1–7.5 6.88 6.78 6.54 A9758 A3594 A7949PIPES 6.1–7.5 6.80 6.76 6.66 P6757 P1851 P8203MOPSO 6.2–7.6 n/a 6.90 6.75 M8389 n/a n/aBis-Tris Propane 6.3–9.5 n/a 6.8, 9.0 n/a B6755 B4679 B9410BES 6.4–7.8 7.17 7.09 6.90 B9879 B4554 B6420MOPS 6.5–7.9 7.28 7.20 7.02 M1254 M3183 M5162TES 6.8–8.2 7.50 7.40 7.16 T1375 T5691 T6541HEPES 6.8–8.2 7.55 7.48 7.31 H3375 H4034 H7273DIPSO 7.0–8.2 n/a 7.60 7.35 D9648 n/a D0306MOBS 6.9–8.3 n/a 7.60 n/a M3295 n/a n/aTAPSO 7.0–8.2 n/a 7.60 7.39 T9269 T5566 T0432Trizma 7.0–9.0 8.20 8.06 7.72 T1503 T6066 T6791HEPPSO 7.1–8.5 n/a 7.80 6.66 H3137 n/a n/aPOPSO 7.2–8.5 n/a 7.80 7.63 P3405 n/a P7088TEA 7.3–8.3 n/a 7.80 n/a T1377 n/a n/aEPPS 7.3–8.7 n/a 8.00 n/a E9502 E0276 E1894Tricine 7.4–8.8 8.16 8.05 7.80 T0377 T5816 T9784Gly-Gly 7.5–8.9 n/a 8.20 n/a G1002 G3915 G7278Bicine 7.6–9.0 8.35 8.26 8.04 B3876 n/a B8660HEPBS 7.6–9.0 n/a 8.30 n/a H6903 n/a n/aTAPS 7.7-9.1 8.49 8.40 8.18 T5130 T5316 T9659AMPD 7.8–9.7 n/a 8.80 n/a A9754 n/a A9074TABS 8.2–9.6 n/a 8.90 n/a T1302 n/a n/aAMPSO 8.3–9.7 n/a 9.00 9.10 A6659 n/a A7585CHES 8.6–10.0 9.55 9.49 9.36 C2885 n/a C8210CAPSO 8.9–10.3 AMP 9.0–10.5 CAPS 9.7–11.1 CABS 10.0–11.4

Pick your pH…Buffers

All of these chemicals on the left are buffers. Each will buffer a solution in a different pH range. For example, if you wanted to make a solution with a stable pH of 8, you can add HEPES. What if you wanted to make a solution with a stable pH of 10?

NEW AIM: Why is pH important?Chapter 2 - The Chemical Basis of Life

AIM: Why is pH important?Chapter 2 - The Chemical Basis of Life

Factories, power plants, etc… burn fossil fuels and release compounds like sulfur dioxide (SO2) and nitrous oxides (NOx), which will react with water and ozone to form sulfuric acid H2SO4 and nitric acid (HNO3), respectively. These acids are then dissolve in rain water forming “acid rain” or “acid precipitation”.


The normal pH of rain is around 5.5 (acidic). This is because water reacts with CO2 in the air to form H2CO3 (carbonic acid).

CO2 + H2O H2CO3 The double arrow means the reaction goes both ways. Make sure you memorize this reaction.


Acid Rain with pH values below 5 can destroy forest and lake ecosystems. Organisms have evolved to function in a narrow pH range. A drastic change in pH can cause our proteins to change structure (denature) and not work properly anymore resulting in death.


This shows a statue in Germany that has been decimated by acid rain. The photo on the left was taken in the 60’s, the one of the right was taken in the 90’s. The statue itself is hundreds of years old.

new aim: what is so important about water? chapter 3 – water and the fitness of the environment

Documents

chemical basis of life

chemical basis of life

o h h chapter

environment slide

o h h aim

lone pair electrons

new aim

shared electrons