Chapter 3: Water and life
How would we make a liter (L) of solution consisting of 1 mol of sucrose dissolved in water?
1. We would measure out 342g of sucrose and then gradually add water, while stirring, until the sugar was completely dissolved. 2. We would add enough water to bring the total volume of the solution 1L 3. At that point, we would have 1-molar (1 M) solution of sucrose
Compared with a basic solution at pH 9, the same volume of an acidic solution at pH 4 has ________ times as many hydrogen ions (H+).
10^5 or 100,000
polar covalent bond
A covalent bond in which electrons are not shared equally
Solution
A homogeneous mixture of two or more substances
What is the relevance of waters high specific heat to life on earth?
A large body of water can absorb and store a huge amount of heat during the day and in summer, while warming only a few degrees. At night and in winter, the gradually cooling water can warm the air. Hence why coastal regions are milder climates than inland regions.
Solvent
A liquid substance capable of dissolving other substances
The concentration of the appetite-regulating hormone gherlin is about 1.3 x 10^-10 M in the blood of a fasting person. How many molecules of ghrelin are in 1 L of blood?
A liter of blood would contain 7.8x10^13 molecules of ghrelin. (1.3x10^-10 moles per liter x 6.02x10^23 molecules per mole)
surface tension
A measure of how difficult it is to stretch or break the surface of a liquid Ex: slightly overfilling a drink or a spider walking across a pond without breaking the surface
hydroxide ion (OH-)
A negatively charged ion made of oxygen and hydrogen.
kilocalorie (kcal)
A quantity of heat equal to 1,000 calories. Used to measure the energy content of food, it is usually called a "Calorie."
Base
A substance that decreases the hydrogen ion concentration in a solution. Ex: ammonia (NH3), for instance , acts as a base when the unshared electron pair in nitrogen's valence shell attracts a hydrogen ion from the solution, resulting in an ammonium ion (NH4+) NH3 + H+ <—-> NH4+
Acid
A substance that increases the hydrogen ion concentration of a solution. Ex: when hydrochloride acid (HCl) is added to water, hydrogen ions dissociate from chlorine ions: HCl —> H+ + Cl-
Solute
A substance that is dissolved in a solution.
Which contains more thermal energy a hot pot of coffee or the water in a swimming pool?
A swimming pool Although the pot of coffee has a much higher temperature than the swimming pool, the swimming pool contains more thermal energy because of its much greater volume
Joule (J)
A unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J.
Most buffer solutions contain
A weak acid and its corresponding base (which combine reversibly with hydrogen ions)
Weak acids are
Acids that reversible release and accept back ions Ex: carbonic acid H2CO3 (carbonic acid) <—> HC3- (bicarbonate ion) + H+ (hydrogen ion)
calorie (cal)
Amount of energy needed to raise temperature 1 gram of water 1 degree C (One convenient unit of heat)
Adhesion
An attraction between molecules of DIFFERENT substances (the clinging of ones substance to another) Ex: water to cell walls by hydrogen bonds helps resist the downward pull of gravity
Compared with most other substances water has
An unusually high specific heat
How can the freezing of water crack boulders?
As water freezes, it expands because water molecules move farther apart in forming ice crystals. When there is water in a crevice of a boulder, expansion due to freezing may crack the rock.
Acetic Acid (CH3COOH) can be a buffer, similar to carbonic acid. Write the dissociation reaction, identifying the acid, base, H+ acceptor, and H+ donor.
CH3COOH = (CH3COO-) + (H+) *CH3COOH is the acid (the H+ donor) *CH3COO- is the base (the H+ acceptor)
Look at figure 3.2 and explain why the central water molecule can hydrogen bond to four (rather then three or five) other water molecules.
Due to its two polar covalent bonds, a water molecule has four regions of partial charge: two positive regions on the two hydrogens and two negative regions on the oxygen atom.
What is electronegativity, and how does it affect interactions between water molecules?
Electronegativity is the attraction of an atom for the electron of a covalent bond. Because oxygen is more electronegative than hydrogen, the oxygen atom in H2O pulls electrons towards itself, resulting in a partial negative charge on the oxygen atom and a partial positive charge on the hydrogen atoms. Oppositely charged ends of water molecules are attracted to each other, forming a hydrogen bond.
What must happen in to break a hydrogen bond?
Heat must be absorbed (by the same token heat is released when hydrogen bonds form)
Explain the saying "It's not the heat; it's the humidity"
High humidity hampers cooling by suppressing the evaporation of sweat
Describe how properties of water contribute to the upward movement of water in a tree.
Hydrogen bonds hold neighboring water molecules together. This cohesion helps the water molecules resist gravity. Adhesion between water molecules and the walls of water-conducting cells also counters gravity. As water evaporates form leaves, the chain of water molecules in water-conducting cells moves upward.
Buffer
Is a substance that minimizes changes in the concentrations of H+ and OH- in a solution
Global warming
Is cause by carbon dioxide and other "greenhouse" gases in the atmosphere, is having a profound effect on ivy environment around the globe
How is a water molecule shaped?
It is shaped like a wide V with its two hydrogen atoms joined to the oxygen atom by a single covalent bond
The ability for ice to float is due to
It's lower density (Which is an important factor in the suitability of the environment for life)
polar molecule
It's overall charge is unevenly distributed
The faster molecules move the greater its
Kinetic energy
Water is one of the few substances that are _______ dense as a solid than a liquid
Less
The properties of water arise from attraction between
Oppositely charged atoms of different water molecules (the partially positive hydrogen of one molecules is attracted to the partially charged negative oxygen of a nearby molecule)
Is oxygen or hydrogen more electronegative?
Oxygen
specific heat
The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree celcius
What would be the effect on the properties of water molecule if oxygen and hydrogen had equal electronegativity?
The covalent bonds of water molecules would not be polar, and water molecules would not form hydrogen bonds with each other.
A water strider (an insect that can walk on water) has legs that are coated with a hydrophobic substance. What might be the benefit? What would happen if the substance were hydrophilic?
The hydrophobic substance repels water, perhaps helping to keep the ends of the legs from becoming coated with water and breaking through the surface. If the legs were coated with the hydrophilic substance, water would be drawn up them, possibly making it more difficult for the water strider to walk on water
mole (mol)
The number of grams of a substance that equals its molecular weight in daltons and contains Avogadro's number of molecules.
Given a liter of pure water and a liter solution of acetic acid, what would happen to the pH if you added 0.01 mol of a strong acid to each? Use the reaction equation to explain the result.
The pH of the water should go fro 7 to about 2; the pH of the acetic acid solution will only decrease a small amount, because the reaction shown in the question above will shift to the left, with CH3 COO- accepting the influx of H+ and becoming CH3 COOH.
Why is it unlikely that two neighboring water molecules would be arranged like this?
The positively charged hydrogen regions would repel each other.
evaporative cooling
The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state.
molecular mass
The sum of the masses of all the atoms in a molecule
thermal energy
The total energy of motion in the particles of a substance
What happens when two objects of differ my temperatures are brought together?
Thermal energy passes from the warmer to the cooler object until the two are the same temperature
The transition from a liquid to a gas is called
Vaporization (or evaporation)
What property supports life on earth and may contribute to the potential for life to have evolved on other planets?
Water
What is the most common substance on earth to exist in the natural environment in all three physical states of matter?
Water (covers 3/4 of the earth's surface)
What would cause an aqueous solution to have an imbalance in H+ and OH- concentration?
When acids dissolve in water they donate additional H+ to the solution
HCl is a strong acid that dissociates in water: HCl —> H+ + Cl- What is the pH of 0.01 M HCl?
[H+] = 0.01 M = 10-2 M, so pH =2
aqueous solution
a solution in which water is the solvent
How does water moderate air temperature?
by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler
What are the four emergent properties of water?
cohesive behavior, ability to moderate temperature, expansion upon freezing, versatility as a solvent
ocean acidification
decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels
kinetic energy
energy of motion
Temperature
represents the average kinetic energy of the particles that make up a material
Most chemical reactions in organisms involve
solutes dissolved in water
Molarity
the number of moles of solute per liter of solution
hydronium ion (H3O+)
the positive ion formed when a water molecule gains a hydrogen ion
heat of vaporization
the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state
hydration shell
the sphere of water molecules around each dissolved ion
heat
thermal energy in transfer from one body of matter to another
Hydrophobic
water hating (non polar) Ex: vegetable oil
Measurements show that the pH of a particular lake is 4.0. What is the hydroxide ion concentration of the lake? (A) 10^-10 M (B) 10^-4 M (C) 10^-7 M (D) 10.0 M
(A) 10^-10 M
Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake? (A) 4.0 M (B) 10^-10 M (C) 10^-4 M (D) 10^4 M
(C) 10^-4 M
Which of the following is a hydrophobic material? (A) paper (B) table salt (C) wax (D) sugar
(C) wax
A slice of pizza has 500 kcal. If we could burn the pizza and use all the heat to warm a 50-L container of cold water, what would be the approximate increase in the temperature of the water? (Note: A liter of cold water weighs about 1 kg.) (A) 50°C (B) 5°C (C) 100°C (D) 10°C
(D) 10°C
We can be sure that a mole of table suave and a mole of vitamin C are equal in their (A) mass (B) volume (C) number of atoms (D) number of molecules
(D) number of molecules
Cohesion
Attraction between molecules of the SAME substance Ex: water from the roots reaches the leaves through a network of water conducting cells
Hydrogen bonding is responsible for water's
Surface tension
hydrogen ion (H+)
an atom of hydrogen that has lost its electron
Hydrophilic
attracted to water (polar) Ex: cotton
What scale do biologists use to describe how acidic or basic a solution is?
pH scale
