Biology hw 3

A compound is an acid if it ...

donates H+ to water

A solution contains only glycerol and fructose. There is ten times as much glycerol as fructose. Therefore, ... both glycerol and fructose are solutes. glycerol is the solvent. glycerol is a solute. fructose is the solvent. None of the above

Glycerol is the solvent

Which of the following can be considered strong bases?

NaOH

Compounds that release OH- are bases because ... (a) OH- combines with H+ and removes it from solution. (b) bases are defined as compounds that release OH-. (c) OH- makes solutions more acidic. Both (a) and (b). None of the above.

(a) OH- combines with H+ and removes it from solution.

Which statement is true of water? (a) The O atom in water has a partial positive charge. (b) The H atoms in water have partial positive charges. (c) Its polarity results from hydrogen's high electronegativity. (d) About 50% of the average cell's mass consists of water. All of the above except for (a).

(b) The H atoms in water have partial positive charges. Good work! H is less electronegative than O, so the shared electrons spend most of their time near O.

Which statement is true of the relation between life and chemical equilibrium?

) Living cells avoid chemical equilibrium by taking in energy and materials.

Under standard conditions the reversible reaction A + B → C + D has a ΔG∘ = -25 kJ/mol. What is ΔG when: T = 475 K, [A] = 0.5M, [B] = 0.2 M, [C] = 0.2 M, and [D] = 0.3 M?

-27 kJ/mol Correct! The nonstandard concentrations have lowered ΔG by 2 kJ.mol.

In the molecule below, how many atoms could make hydrogen bonds with water? Part D number 14 Dont know how to do this

10

Factory smoke has led to acid rain that lowered the pH of a lake to 5.0. What is the H+ concentration in the lake?

10^-5 M

In a washing machine, the detergent raised the pH to 9.0. The concentration of OH- in the solution is

10^-5 M Good work! If you divide 10-14 by 10-9 M (the H+ concentration at pH 9), you get 10-5 M, the OH- concentration.

How many atoms in the pictured molecule can form hydrogen bonds with water molecules? Its a pic of NC2O

5 Correct! O and N can make hydrogen bonds, as can each H attached to O or N.

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. A buffer prevents the pH of a solution from changing when an acid or base is added. A buffer causes acidic solutions to become alkaline, and alkaline solutions to become acidic. Buffered solutions are always neutral, with a pH of 7. A buffer stabilizes the pH of a solution by preventing acids or bases from dissociating.

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. Correct In this fashion, buffers minimize the change in the pH of a solution.

Cells are surrounded by water, and cells themselves consist of about 70-95% water. Which of the following occurs as a result? -Dissolved substances can be easily transported within a cell or between cells in multicellular organisms. -The temperature of living things tends to change relatively slowly. -A variety of nutrient molecules is readily available as dissolved solutes. -Waste products produced by cell metabolism can be easily removed. -All of the listed responses are correct.

All of the listed responses are correct.

Ammonia reacts with water as shown below. Which statement best explains why ammonia is considered to be a base? -The reaction decreases the amount of water in the solution. Bases are compounds that remove H+ from solutions. Bases are defined as compounds that add OH- to the solution. NH4 + can donate H+ to hydronium. None of the above. Ammonia is not a base.

Bases are compounds that remove H+ from solutions.

A solution is very acidic if it ... (a) has a very low pH value. (b) has a high hydronium ion concentration. (c) has a very low hydronium ion concentration. Both (a) and (b). Both (a) and (c).

Both a and b

Which of the following can be considered bases? (a) Na2CO3 (b) KOH (c) NaCl Both (a) and (b). All of the above.

Both a and b

The dissociation of water ... (a) releases free H+ ions into the solution. (b) is quickly reversed, giving neutral water molecules. (c) involves pairs of water molecules. Both (a) and (b). Both (b) and (c).

Both b and c

In the equation ΔG = ΔH - TΔS, the change in the amount of disorder in the system is symbolized by ...

Delta S

In water, every sulfuric acid molecule transfers H+ to water and becomes an HSO4 - ion. Some HSO4 - ions give off another H+ to form SO4 -2 ions. Which statement is true?

H2SO4 is a strong acid and HSO4 - is a weak acid. Good choice. Every H2SO4 molecule donates H+, so H2SO4 is a strong acid. Not all molecules of HSO4 - donate H+, so HSO4 - is a weak acid.

In water, phosphoric acid dissociates according to the chemical reactions written below. Which of the following statements about the dissociation of phosphoric acid is true?

H3PO4, H2PO4 - and HPO4 2- are all weak acids. Yes! All 3 do not dissociate completely, so they are all weak acids.

Which of the following dissociations is that of an acid? NH3 + H+ → NH4+ KOH → K+ + OH- H2O → H+ + OH- HF → H+ + F- NaOH → Na+ + OH-

HF --> H+ + F- Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion.

Which bonding found here is the weakest?

Hydrogen Bonds are weaker than covalent bonds because they do not involve sharing of electrons, and they are weaker than ionic bonds because they involve the attraction of partial (not full) opposite charges.

Which of the following occurs because molecules of water are farther apart in ice than in liquid water?

Ice floats

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

Ice floats because it is less dense than liquid water; floating ice insulates water below and provides a habitat for some species. The significant increase in Arctic air temperature over the past 50 years is causing a reduction in sea ice, compromising these beneficial effects of sea ice.

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.

Which statement is true of the equation shown below? It omits an important water molecule. It is a standard shorthand for water dissociation. It is correct in showing H+as a product of water dissociation. It omits an important water molecule and it is a standard shorthand for water dissociation. All of the above. None of the above.

It omits an important water molecule and it is a standard shorthand for water dissociation.

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 answer helps to explain how many hydrogen bonds a water molecule can form?

Oxygen's valence shell has four orbitals.

Your tank of swamp fish needs a pH of 5, and the pH is 7 at present. What should you do to the H+ concentration?

Raise it to 100 times its present value Yes! Quick, do it! Each pH unit is a 10-fold change in H+ concentration.

Your tank of alkali fish needs a pH of 8, and the pH is 6 at present. What should you do to the H+ concentration?

Reduce it to 1/100 of its present value. Yes! Quick, do it! Each pH unit is a 10-fold change in [H+].

What conditions must be met in order for an aqueous solution to be called "neutral"?

The concentrations of hydronium and hydroxide ions are equal.

If water were NOT a polar molecule, how would the effects of global warming differ from those 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.

A chemist calculates that a certain reaction would result in ΔH = -9 kJ and TΔS = +1 kJ. What can you conclude?

The reaction will occur spontaneously, because it decreases G. You know your stuff! ΔG = ΔH - TΔS = -9 -(-1) = -8. Since the free energy decreases, the reaction will run spontaneously.

dentify all correct statements about the ionization of water. Check all that apply. Water ionizes to form hydroxide and hydronium ions. Dissociation of water is reversible. Water ionizes to form peroxide and hydronium ions. Dissociation of water is not reversible. Dissociation of water produces equal numbers of OH- and H+. Dissociation of water produces equal masses of OH- and H+.

Water ionizes to form hydroxide and hydronium ions. Dissociation of water is reversible. Dissociation of water produces equal numbers of OH- and H+.

Dr. Haxton told his class that a water molecule can make 4 hydrogen bonds, all of them in the same plane as the three atoms. What would a good student reply?

Wrong! Two hydrogen bonds are not in the plane of the atoms.

Which statement is part of the explanation for water's high cohesion? (a) Oxygen has four valence orbitals. (b) Oxygen is much more electronegative than hydrogen. (c) Water can hydrogen-bond with other kinds of molecules. All of the above. Both (a) and (b).

a and b Correct Good choice! The electronegativity difference creates charges that make hydrogen bonds possible, and the four outer orbitals permit water to make four hydrogen bonds. The result is a three-dimensional network of bonds between water molecules.

The reaction shown below is at equilibrium. What could you do to make this reaction produce more methyl benzoate? (a) Add more benzoic acid. (b) Remove some methanol (HOCH3). (c) Remove some water. (d) Add more water. Both (a) and (c).

a and c Yes! By removing water, you slow the reverse reaction; by adding a reactant, you speed the forward reaction. Both changes make the forward reaction faster than the reverse reaction. Therefore, the reaction will produce more methyl benzoate as it returns to equilibrium.

An acid is __________.

a compound that donates hydrogen ions to a solution

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

A 1 M solution contains ...

a) one mole of solute per liter of solution.

Polar attractions are ... (a) forces between atoms with partial charges. (b) weaker than covalent bonds. (c) important because they are numerous. (a) and (b) are true. (c) is false. (a), (b), and (c) are correct.

a, b, and c Right! Polar attractions occur between atoms with partial charges and are weaker than covalent bonds. Still, they're important because so many of them occur in living cells.

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

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

Why isn't this insect drowning?

surface tension

Hydrogen bonds ... can form between H and N. are covalent bonds. occur within a water molecule. share electrons between the two bonded atoms. All of the above.

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

Cohesion of water Tree What process is illustrated by this animation?

evaporation

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

four.... hydrogen

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

Which type of bond must be broken for water to vaporize?

hydrogen bonds

The bonds that are broken when water vaporizes are

hydrogen bonds between water molecules.

Despite its cohesion, water can flow because ...

hydrogen bonds break and re-form rapidly.

A molecule that has all nonpolar covalent bonds would be __________.

hydrophobic

What are nonpolar molecules that cluster away from water molecules called?

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 organisms that produce calcium carbonate shells

An acid is a substance that _____.

increases the hydrogen ion concentration of an aqueous solution

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.

A strong acid like HCl is a strong buffer at low pH. ionizes completely in an aqueous solution. reacts with strong bases to create a buffered solution. both ionizes completely in aqueous solutions and is a strong buffer at low pH. increases the pH when added to an aqueous solution.

ionizes completely in 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

To determine whether a base is weak or strong, ...

look for undissociated molecules of base.

Adding a base tends to __________ of a solution. lower the hydrogen ion concentration and lower the pH lower the hydrogen ion concentration and increase the pH increase the hydrogen ion concentration and lower the pH increase the hydrogen ion concentration and increase the pH lower the hydroxide ion concentration and lower the pH

lower the hydrogen ion concentration and increase the pH

Which answer is a true statement about pH values? Stomach juice has a high pH. pH is important in life mainly because it affects the cohesion of water. A high pH corresponds to a high H+ concentration. Pure water has a pH of 0. None of the above.

none of the above

Hydrophobic substances such as vegetable oil are _____.

nonpolar substances that repel water molecules

The water molecule has a bent shape because ...

oxygen has two unbonded pairs of valence electrons. That's right! Repulsion between electrons governs the angles between bonds. The two pairs of unbonded electrons repel the two pairs of bonding electrons, creating the bend in the molecule.

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

polar

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

polar Correct 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.

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

polar covalent

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

polar covalent Correct While oxygen shares electrons with hydrogen, the electrons spend more time with the oxygen than with the hydrogens.

Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature?

the absorption of heat by the breaking of hydrogen bonds

The partial negative charge in a molecule of water occurs because _____.

the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus

For the reaction ATP + H2O → ADP + Pi, the change in standard free energy (ΔG∘) is -30.5 kJ/mol. From this information we can conclude that ...

the forward reaction will be spontaneous under standard conditions. Correct! Did you draw that conclusion by noting that ΔG∘ is less than zero?

A solution is aqueous if ...

water is the solvent

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

water's high heat of vaporization

Which of the following is a hydrophobic material? table salt wax paper sugar pasta

wax