Biol 1406 Ch.3

surface tension

A measure of how difficult it is to stretch or break the surface of a liquid

Solute

A substance that is dissolved in a solution.

Aqueous Solvent

a solution that uses water as the solvent ( water is called the universal solvent because most solutions use water as the solvent)

Buffers work best when ...

about half of the buffer molecules are dissociated

Though you add heat, the temperature of boiling water remains constant because ...

it takes energy to break hydrogen bonds.

Which property of water allows dogs to cool themselves by panting?

water's high heat of vaporization

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

1000 (A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 × 10 × 10 ≡ 1,000.)

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 (In fact, this is the number of molecules in one mole of any substance.)

Solution

A homogeneous mixture of two or more substances

Look at the figure showing the pH values of some familiar aqueous solutions. What is the difference between H+ concentration in an acidic solution such as lemon juice (pH 2) and a basic solution such as household bleach (pH 13)?

The H+ concentration of lemon juice is higher than the H+ concentration of household bleach by a factor of 1011 (100 billion).

high specific heat

The ability of water to resist changes in temperature.

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

polar (The electrons spend more time with the oxygen of the water molecule than with the hydrogens of water. Thus, the oxygen has a net negative charge and the hydrogens have a net positive charge.)

Which of the following helps most to explain why water has a high specific heat? (a) A water molecule can make 4 hydrogen bonds. (b) The water molecule has exceptionally strong covalent bonds. (c) Water temperature is exceptionally sensitive to heat.

(a) A water molecule can make 4 hydrogen bonds.

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 (The polarity of a water molecule allows the oxygen of one water molecule to bond weakly to the hydrogen of another water molecule)

Which statement is true of water's tensile strength?

-It results from hydrogen bonding. -It helps to pull water through plants. -It involves both cohesion and adhesion

Which factor is important in making it possible to cool yourself by sweating?

-Molecules collide with varied angles and speeds. -Hydrogen bonds are relatively weak.

Which statement helps to explain why ice is less dense than liquid water?

-Water molecules make hydrogen bonds at definite angles. -Cold molecules move less than warm molecules.

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

1 calorie (The specific heat of liquid water is 1 cal⁄g°C.)

A buffer consists of undissociated acid (HA) and the ion made by dissociating the acid (A-). How does this system buffer a solution against decreases in pH?

A- reacts with H+ to become HA.

Which answer helps to explain why all living cells need pH buffers?

Amino acid side chains have many carboxyl and amino groups.

Cohesion

Attraction between molecules of the same substance

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

Electronegativity

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

High Specific Heat (Water has a high specific heat, meaning that a relatively large amount of heat must be added or removed in order to get the temperature to change significantly.)

How does the way a buffer stabilizes pH during addition of acid differ from the way the same buffer stabilizes pH during addition of base?

It's the same reaction running backward or forward

In this molecule, what type of bond is found between the oxygen and hydrogens?

Polar covalent (While oxygen shares electrons with hydrogen, the electrons spend more time with the oxygen than with the hydrogens.)

Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?

Polar groups attract one another. (Polar water molecules pull together, holding the polar parts of the amphipathic molecules and squeezing out the nonpolar parts. That leaves the nonpolar parts waving in the air.)

Why doesn't oil mix with water?

Polar molecules attract one another.

How does the pH of the solution on the right compare with that of the solution on the left?

The solution on the right is basic relative to the solution on the left.

Which statement is true of pH buffers?

They consist of weak acids and weak bases.

Dissolving is best described as ...

a mingling of molecules and/or ions. When sugar dissolves in water, the sugar molecules remain intact but mingle with water molecules. When salt (NaCl) dissolves, its Na+ and Cl- ions separately mingle with water.

aqueous solution

a solution in which water is the solvent

The open spaces in water's crystal structure make it possible for ...

aquatic life to exist at the North Pole.

Many of water's emergent properties, such as its cohesion, high specific heat, and 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

Water has surface tension because ...

hydrogen bonds between surface water molecules resist being stretched.

Buffer

compound that prevents sharp, sudden changes in pH

Global warming is causing atmospheric CO2 levels to increase, which is expected to cause ocean acidification. Which of the following is NOT a consequence of increased atmospheric CO2 levels?

decrease in the concentration of bicarbonate ions in the oceans (The concentration of bicarbonate ions is expected to increase. As more atmospheric CO2 dissolves into seawater, more carbonic acid is formed. The carbonic acid then dissociates into bicarbonate ions and hydrogen ions. The hydrogen ions combine with carbonate ions to form even more bicarbonate ions.)

A water molecule can bond to up to _____ other water molecules by ____ bonds.

four, hydrogen

To make a buffer, you need to ...

have a weak acid or a weak base half ionized in water

Water is a source of ______________ for chemical reactions in cells.

hydrogen atoms and oxygen atoms

What is the arrow pointing to?

hydrogen ion

In a neutral solution the concentration of _____.

hydrogen ions is equal to the concentration of hydroxide ions

What is the arrow pointing to?

hydroxide ion

An acid is a substance that __________.

increases the hydrogen ion concentration of an aqueous solution (As an acid dissociates, it donates a hydrogen ion to the solution.)