The unequal sharing of electrons within a water molecule makes the water molecule _____. |
polar |
The tendency of an atom to pull electrons toward itself is referred to as its _____. |
electronegativity |
In this water molecule, what type of bond is found between the oxygen and hydrogens? |
polar covalent |
Know which bonds are the weakest by looking at picture |
… |
Why isn’t this insect drowning? |
surface tension |
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 |
Cohesion of water Tree What process is illustrated by this animation? |
evaporation |
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 |
Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water’s _____. |
high specific heat |
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 |
Which type of bond must be broken for water to vaporize? |
hydrogen bonds |
An acid is a substance that _____. |
increases the hydrogen ion concentration of an aqueous solution |
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. Correct In this fashion, buffers minimize the change in the pH of a solution. |
The bonds that are broken when water vaporizes are |
hydrogen bonds between water molecules. |
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 |
A strong acid like HCl |
ionizes completely in an aqueous solution. |
Which of the following is a hydrophobic material? |
wax |
Polar attractions are … |
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. |
Hydrogen bonds … |
can form between H and N |
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. |
In the molecule below, how many atoms could make hydrogen bonds with water? |
10 |
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 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. |
Despite its cohesion, water can flow because … |
hydrogen bonds break and re-form rapidly. |
Which answer helps to explain how many hydrogen bonds a water molecule can form? |
Oxygen’s valence shell has four orbitals. |
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 |
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 |
Water molecules can form hydrogen bonds with ___ |
compounds that have polar covalent bonds |
A solution contains only glycerol and fructose. There is ten times as much glycerol as fructose. Therefore, … |
Glycerol is the solvent |
A solution is aqueous if … |
water is the solvent |
A 1 M solution contains … |
a) one mole of solute per liter of solution. |
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. |
Which statement is true of water? |
(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. |
Hydrophobic substances such as vegetable oil are _____. |
nonpolar substances that repel water molecules |
Which type of bond must be broken for water to vaporize? |
hydrogen bonds |
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 |
Understanding parts of graph Ch3 item 2 |
… |
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-). |
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 |
Which property of water allows dogs to cool themselves by panting? |
water’s high heat of vaporization |
Cells are surrounded by water, and cells themselves consist of about 70-95% water. Which of the following occurs as a result? |
All of the listed responses are correct. |
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. |
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. |
Which of the following occurs because molecules of water are farther apart in ice than in liquid water? |
Ice floats |
A molecule that has all nonpolar covalent bonds would be __________. |
hydrophobic |
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. |
Ammonia reacts with water as shown below. Which statement best explains why ammonia is considered to be a base? |
Bases are compounds that remove H+ from solutions. |
Which of the following can be considered bases? |
Both a and b |
Compounds that release OH- are bases because … |
(a) OH- combines with H+ and removes it from solution. |
To determine whether a base is weak or strong, … |
look for undissociated molecules of base. |
Which of the following can be considered strong bases? |
NaOH |
A solution is very acidic if it … |
Both a and b |
The dissociation of water … |
Both b and c |
Which statement is true of the equation shown below? |
It omits an important water molecule and it is a standard shorthand for water dissociation. |
What are nonpolar molecules that cluster away from water molecules called? |
hydrophobic |
A compound is an acid if it … |
donates H+ to water |
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 answer is a true statement about pH values? |
none of the above |
What conditions must be met in order for an aqueous solution to be called "neutral"? |
The concentrations of hydronium and hydroxide ions are equal. |
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 |
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. |
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. |
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+]. |
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. |
An acid is __________. |
a compound that donates hydrogen ions to a solution |
Adding a base tends to __________ of a solution. |
lower the hydrogen ion concentration and increase the pH |
Which of the following dissociations is that of an acid? NH3 + H+ → NH4+ |
HF –> H+ + F- Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion. |
dentify all correct statements about the ionization of water. |
Water ionizes to form hydroxide and hydronium ions. Dissociation of water is reversible. Dissociation of water produces equal numbers of OH- and H+. |
Which statement is true of the relation between life and chemical equilibrium? |
) Living cells avoid chemical equilibrium by taking in energy and materials. |
The reaction shown below is at equilibrium. What could you do to make this reaction produce more methyl benzoate? (a) Add more benzoic acid. |
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. |
In the equation ΔG = ΔH – TΔS, the change in the amount of disorder in the system is symbolized by … |
Delta S |
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. |
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? |
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. |
Each water molecule is joined to _____ other water molecules by ____ bonds. |
four…. hydrogen |
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. |
The tendency of an atom to pull electrons toward itself is referred to as its _____. |
electronegativity |
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. |
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. |
Biology hw 3
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