Chapter 3: Water and Life

A mole of ethyl alcohol weighs 46 g. How many grams of ethyl alcohol are needed to produce 1 L of a 2-millimolar (2 mM) solution?

0.092 g

When an ionic compound such as sodium chloride (NaCl) is placed in water, the component atoms of the NaCl crystal dissociate into individual sodium ions (Na+) and chloride ions (Cl−). In contrast, the atoms of covalently bonded molecules (e.g., glucose, sucrose, glycerol) do not generally dissociate when placed in aqueous solution. Which of the following solutions would be expected to contain the greatest number of solute particles (molecules or ions)?

1 L of 1.0 M NaCl

About _____ molecules in a glass of water are dissociated.

1 in 500,000,000

Assume that acid rain has lowered the pH of a particular lake to pH 4.0. What is the hydroxyl ion concentration of this lake?

1 × 10-10 mol of hydroxyl ion per liter of lake water

What is the charge on a hydronium ion?

1+

A pH of 6 is how many times more acidic than a pH of 9?

1,000

A dietary Calorie equals 1 kilocalorie. Which of the following statements correctly defines 1 kilocalorie?

1,000 calories, or the amount of heat required to raise the temperature of 1 kg of water by 1°C

What is the charge on a hydroxide ion?

1-

If the pH of a solution is increased from pH 5 to pH 7, it means that the

10,000 times more

A solution at pH 6 contains _____ than the same amount of solution at pH 8.

100 times more H+

What is the pH of an aqueous solution with the hydronium ion concentration [H3O+] = 2 x 10-14 M ?

13.7

How much carbon dioxide from the atmosphere is absorbed by the oceans on a daily basis?

20 million metric tons

If the molecular mass of a carbon atom is 12, the mass of a hydrogen atom is 1, and the mass of an oxygen atom is 16 daltons, how many molecules does one mole of table sugar (sucrose; C12H22O11) contain?

6.02 x 10^23

You have a freshly prepared 0.1 M glucose solution. Each liter of this solution contains how many glucose molecules?

6.02 × 10^23

Carbonated cola is more acidic than coffee or even orange juice because cola contains phosphoric acid. What is the molar concentration of [H3O+] in a cola that has a pH of 3.120? (For help with significant figures, see Hint 3.)

7.59 × 10−4

Select the statement that best describes a buffer.

A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.

Which of the following effects is produced by the high surface tension of water?

A raft spider can walk across the surface of a small pond.

How would acidification of seawater affect marine organisms?

Acidification would decrease dissolved carbonate concentrations and hinder growth of corals and shell-building animals.

What do cohesion, surface tension, and adhesion have in common with reference to water?

All are properties related to hydrogen bonding.

Carbon dioxide (CO2) is readily soluble in water, according to the equation CO2 + H2O ↔ H2CO3. Carbonic acid (H2CO3) is a weak acid. Respiring cells release CO2 into the bloodstream. What will be the effect on pH of blood as that blood first comes in contact with respiring cells?

Blood pH will decrease slightly.

Which of the following are consequences of ocean acidification? Select all that apply.

Corals and coral reefs are not able to form their hard skeletons. Clams, mussels, lobsters, and shrimp are not able to form strong enough shells.

The molar mass of glucose (C6H12O6) is 180 g/mol. Which of the following procedures should you carry out to make a 0.5 M solution of glucose?

Dissolve 90 g of glucose in a small volume of water, and then add more water until the total volume of the solution is 1 L.

Which of these is the correct equation for the dissociation of water?

H2O + H2O <==> H3O+ + OH

Which of the following dissociations is that of an acid?

HF → H+ + F

If the pH of a solution is increased from pH 5 to pH 7, it means that the

If the pH of a solution is increased from pH 5 to pH 7, it means that the

What water-related evidence do scientists have that suggests life may exist on other planets?

In 2008, the robotic spacecraft Phoenix found ice present just under the material on Mars's surface, and detected sufficient water vapor in the Martian atmosphere for frost to form.

Why are cell membranes composed primarily of hydrophobic molecules?

In order to perform their function of separating the aqueous solutions outside of cells from the aqueous solutions inside of cells, cell membranes cannot be soluble in water.

A 0.01 M solution of a substance has a pH of 2. What can you conclude about this substance?

It is a strong acid that ionizes completely in water.

Which of the following statements is true about acid precipitation?

It washes away some minerals that are plant nutrients, and causes some toxic minerals to accumulate

Which of the following takes place as an ice cube cools a drink?

Kinetic energy in the drink decreases.

Why is the increasing amount of carbon dioxide being taken up by the oceans a cause for concern?

More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to a decrease in the concentration of carbonate ion (CO32-)

Which of the following ionizes completely in solution and is considered to be a strong base (alkali)?

NaOH

How are oyster larvae affected by ocean acidification?

Oyster larvae cannot grow shells in acidified ocean waters.

Imagine that organisms consisted of 70-95% alcohol instead of 70-95% water. Alcohol's specific heat is about half that of water. How would living things be different?

Systems for temperature regulation would have to be much more efficient

If water were not a polar molecule, how would the effects of global warming differ from what are currently observed or predicted to occur in the future?

The effects would be drastically worse because the loss of the polar nature of water would greatly reduce its specific heat and its ability to moderate temperature.

The molar mass of glucose is 180 g/mol. Which of the following procedures should you carry out to make a 1 M solution of glucose?

The molar mass of glucose is 180 g/mol. Which of the following procedures should you carry out to make a 1 M solution of glucose?

Which of the following accurately relates the emergent properties of water to the effects of global warming in the Arctic?

The significant increase in Arctic air temperature over the past 50 years is causing sea ice to form later in the year, to melt earlier, and to cover a smaller area each year.

An acid is _____.

a compound that donates hydrogen ions to a solution

One of the buffers that contribute to pH stability in human blood is carbonic acid (H2CO3). Carbonic acid is a weak acid that, when placed in an aqueous solution, dissociates into a bicarbonate ion (HCO−3 and a hydrogen ion (H+). Thus, H2CO3 ↔ HCO−3 + H+ If the pH of the blood increases, one would expect this to lead to

a decrease in the concentration of H2CO3 and an increase in the concentration of HCO−3

Water molecules have _____ than molecules of similar size, such as ammonia and methane, reflecting its capacity to absorb large amounts of heat.

a higher boiling point

The partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water molecule. What is this attraction called?

a hydrogen bond

What is the main reason that the oceans are becoming more acidic?

absorption by the oceans of carbon dioxide generated by burning fossil fuels

A given solution contains 0.0001(10-4) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?

acidic: will give H+ to weak acids, but accept H+ from strong acids

Sodas typically contain sugar, flavorings, coloring agents, and carbon dioxide dissolved in water. The best term to describe this mixture would be _____.

an aqueous solution

Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _____.

are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively

The ability of water molecules to form hydrogen bonds with other water molecules and water's ability to dissolve substances that have charges or partial charges are _____.

both caused by water's partial charges

A substance that minimizes changes in the concentration of H+ and OH- in a solution is a _____.

buffer

What is the chemical reaction responsible for the oceans becoming more acidic?

carbon dioxide reacts with seawater, forming carbonic acid

If the pH of a solution is decreased from 9 to 8, it means that the

concentration of H+ has increased tenfold (10X) and the concentration of OH- has decreased to one-tenth (1/10) what they were at pH 9

Which action would involve the greatest transfer of heat?

condensing 5 g of steam to liquid water

The tendency of an atom to pull electrons toward itself is referred to as its _____.

electronegativity

Pure water has a pH of 7. Why does uncontaminated rainwater have a pH of 5.6?

formation of carbonic acid from carbon dioxide and water

Each water molecule is joined to _____ other water molecules by ____ bonds.

four ... hydrogen

Hydrophilic substances, but not hydrophobic substances, _____.

have charges and partial charges to which water molecules can adhere

Sweating has a cooling effect because of water's high _____.

heat of vaporization

Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____.

high specific heat

Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____.

hydrogen bonds

In a neutral solution the concentration of _____.

hydrogen ions is equal to the concentration of hydroxide ions

A molecule that has all nonpolar covalent bonds would be _____

hydrophobic

Nonpolar molecules that cluster away from water molecules are called _____ molecules.

hydrophobic

The absorption of human-generated CO2 by the oceans _____.

increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for calcifying organisms

An acid is a substance that _____.

increases the hydrogen ion concentration of an aqueous solution

The amount of energy that must be absorbed or lost to raise or lower the temperature of 1 g of liquid water by 1°C _____.

is 1 calorie

Adding a base tends to _____ of a solution.

lower the hydrogen ion concentration and increase the pH

Adding acid tends to _____ of a solution

ncrease the hydrogen ion concentration and lower the pH

Most of water's unique features (for example, its versatility as a solvent, ability to moderate temperature, and cohesive behavior) result from the fact that _____.

oxygen attracts electrons more than hydrogen does

What is the pH of a 1 millimolar NaOH solution?

pH 11

What is the pH of a solution with a hydroxyl ion [OH−] concentration of 10-12 M?

pH 2

The unequal sharing of electrons within a water molecule makes the water molecule _____.

polar

Water is a very versatile solvent because water molecules are _____

polar

what type of bond is found between the oxygen and hydrogens?

polar covalent

In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by

polar covalent bonds.

Hydrophobic molecules are _____ water.

repelled by

Because of ocean acidification, the price of which of the following foods is most likely to increase?

shellfish

The reason that coastal climates are more moderate than inland climates is due primarily to water's high _____.

specific heat

Sucrose has a molecular mass of 342 daltons. To make a 2-molar (2 M) solution of sucrose, _____.

stir 342 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 0.5 L

Most acid precipitation results from the combination of _____ with water in the atmosphere, forming strong acids that fall with rain or snow.

sulfur oxides and nitrogen oxides

You can fill a glass of water to just slightly above the rim without it spilling over the glass. What property of water best explains this phenomenon?

surface tension

A glass of grapefruit juice, at pH 3, contains _____ H+ as a glass of tomato juice, at pH 4

ten times as much

Adhesion is best described as _____.

the clinging of one substance to another substance

If a solution has a pH of 7, this means that

the concentration of H+ ions in the water equals the concentration of OH− ions in the water.

The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as _____

the heat of vaporization of that substance

Water is a polar molecule. This means that _____.

the opposite ends of the molecule have opposite electrical charges

In a group of water molecules, hydrogen bonds form between _____.

the oxygen atom in one water molecule and a hydrogen atom in another water molecule

The amount of heat required to change the temperature of 1 g of any substance by one °C is defined as _____.

the specific heat of that substance

The partial charges on a water molecule occur because of _____.

the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule

Some substances, such as oil and gasoline, will not dissolve in water because _____.

their molecules have no charges or partial charges to which water molecules can adhere

The phenomenon responsible for maintaining the upward movement of water through a vessel is _____.

cohesion

What percentage of a cell is composed of

70-95%

When the pH of a solution shifts from 7 to 3, how has the hydrogen ion concentration changed?

It has increased by 10,000 times.

Because molecules of water are farther apart in ice than in liquid water, _____

ice floats

A strong acid like HCl

ionizes completely in an aqueous solution