Biology Chapter 3 HW
Which factor is important in making it possible to cool yourself by sweating? Think carefully!
(A) Molecules collide with varied angles and speeds and (B) Hydrogen bonds are relatively weak.
Which statement helps to explain why ice is less dense than liquid water?
(A) Water molecules make hydrogen bonds at definite angles and (B) Cold molecules move less than warm molecules.
Polar attractions are _____
(A) forces between atoms with partial charges, (B) weaker than covalent bonds, and (C) important because they are numerous.
Dissolving is best described as _____
A mingling of molecules and/or ions
Which of the following helps most to explain why water has a high specific heat?
A water molecule can make 4 hydrogen bonds
A pH of 6 is how many times more acidic than a pH of 9?
1,000
In the molecule below, how many atoms could make hydrogen bonds with water?
10
A solution with a pH of 2 has how many more protons in it than a solution with a pH of 4?
100 times more
What is the pH of an aqueous solution with the hydronium ion concentration [H3O+] = 2 x 10-14 M ?
13.7
Rank the following from most acidic to least acidic. Rank these items from most acidic to least acidic. To rank items as equivalent, overlap them.
2, 3, 5, 6, 14
How many atoms in the pictured molecule can form hydrogen bonds with water molecules?
5
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?
7.59 * 10-4 M Instructions: [H3O+]=10−pH[H3O+]=10−pH [H3O+]=10−3.120[H3O+]=10−3.120 [H3O+]=7.59×10−4M[H3O+]=7.59×10−4M
What is 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.
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
Which of the following can be attributed to water's high specific heat?
A lake heats up more slowly than the air around it
Why doesn't oil mix with water?
Polar molecules attract one another.
Why does ice float in liquid water?
Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water.
Rank, from low to high, the pH of blood, stomach acid, and urine.
Stomach acid, urine, blood
The table shown here lists the specific heat of several substances: Substance Specific heat J/g/∘C Water 4.18 Ethyl alcohol 2.44 Benzene 1.80 Sulfuric acid 1.40 Based on the information in the table, which of the following statements are true?
Sulfuric acid is less resistant to temperature change than water. Benzene is more resistant to temperature change than sulfuric acid. More heat is required to raise the temperature of 1 g of water 1 ∘C than to raise the temperature of 1 g of ethyl alcohol 1 ∘C. Water has a high specific heat due to the hydrogen bonding between water molecules.
Why didn't the insect drown?
Surface tension
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.
Buffers work best when ____
About half of the buffer molecules are dissociated.
Which answer helps to explain why all living cells need pH buffers?
Amino acid side chains have many carboxyl and amino groups.
The open spaces in water's crystal structure make it possible for ____
Aquatic life to exist at the North Pole
Cohesion, surface tension, and adhesion are the properties of water molecules that ________.
Are a result of hydrogen bonding
Hydrogen bonds ____
Can form between H and N
Water molecules can form hydrogen bonds with _____.
Compounds that have polar covalent bonds
The tendency of an atom to pull electrons toward itself is referred to as its _____.
Electronegativity
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.
Which bond is the weakest?
Hydrogen (dotted line)
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
What is the arrow pointing to?
Hydrogen Ion
Water is a source of ______________ for chemical reactions in cells.
Hydrogen atoms and oxygen atoms
Water has surface tension because ____
Hydrogen bonds between surface water molecules resist being stretched.
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
which statement is true of waters tensile strength?
It results from hydrogen bonding, it helps to pull water through plants, it involves both cohesion and adhesion.
Though you add heat, the temperature of boiling water remains constant because _____
It takes energy to break hydrogen bonds
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.
Hydrophobic substances such as vegetable oil are _____.
Nonpolar substances that repel water molecules
The unequal sharing of electrons within a water molecule makes the water molecule _____.
Polar
In this molecule, 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
Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?
Polar groups 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.
Cohesion
Water molecules attracted to each other or a drop of water spilled on a table forms a drop on the table , rather than spreading
Adhesion
Water molecules cling to other objects
