Chapter 3 Mastering

About _____ molecules in a glass of water are dissociated. 1 in 5,000,000 1 in 1,000,000 1 in 1,000,000,000 1 in 500,000,000 1 in 2

1 in 500,000,000

What is the charge on a hydronium ion? 1- 2- 1+ 0 2+

1+ The formation of hydronium results in the gain of 1 more proton than electron.

How did this molecule form? A water molecule split in half. A hydrogen molecule bonded with an OH- molecule. Evaporation. A water molecule gained an hydrogen ion from another water molecule. Two water molecules bonded.

A water molecule gained an hydrogen ion from another water molecule.

Water is a source of ______________ for chemical reactions in cells. (a) hydrogen atoms (b) oxygen atoms (c) energy Both (a) and (b) (a), (b), and (c).

Both (a) and (b) Many reactions incorporate O and H from water into biological molecules. This happens when you digest starch and protein, for example.

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).

Both (a) and (b). 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

Which statement helps to explain why ice is less dense than liquid water? (a) Water molecules make hydrogen bonds at definite angles. (b) Cold molecules move less than warm molecules. (c) Hydrogen bonds lengthen in the cold. All of the above. Both (a) and (b).

Both (a) and (b). The ice lattice has open spaces because of the angles at which hydrogen bonds form. Heat energy can break water molecules free of the lattice so they move into the openings.

Which of these is the correct equation for the dissociation of water? H2O + H2O+<==> H2O + OH- H2O <==> H+ + OH- H2O + OH-<==> H2O+ H+<==> H2O + H2O+ H2O + H2O <==> H3O+ + OH-

H2O + H2O <==> H3O+ + OH-

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

None of the above.

Which answer helps to explain how many hydrogen bonds a water molecule can form? Water can ionize, making hydronium and hydroxide ions. The angle between H-O bonds in water is 180∘. The oxygen atom has six protons. Oxygen makes two covalent bonds. Oxygen's valence shell has four orbitals.

Oxygen's valence shell has four orbitals. Each of those orbitals can engage in a hydrogen bond.

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? Reduce it to 1/100 of its present value. Double it. Cut it in half. Raise it to 100 times its present value. Raise it to 200 times its present value.

Raise it to 100 times its present value. 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? Double it. Raise it to 100 times its present value. Reduce it to 1/100 of its present value. Reduce it to 1/200 times its present value. Cut it in half.

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

Dissolving is best described as ... a change from a solid to a liquid. molecules breaking into ions. breaking covalent bonds. a mingling of molecules and/or ions. a separation of molecules into neutral atoms.

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.

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

electronegativity

The unequal sharing of electrons within a water molecule makes the water molecule _____. have a low surface tension change easily from a liquid to gaseous form hydrophobic polar ionic

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.

In this molecule, what type of bond is found between the oxygen and hydrogens? nonpolar covalent hydrophilic ionic polar covalent hydrophobic

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

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

glycerol is the solvent. In any solution, the most abundant substance is the solvent.

Water has surface tension because ... molecules at the surface make more hydrogen bonds. hydrogen bonds between surface water molecules resist being stretched. water tends to evaporate from the surface. there is positive pressure inside the water mass. cohesion forces are weaker at the surface.

hydrogen bonds between surface water molecules resist being stretched. The hydrogen bonds between surface water molecules are normally slightly stretched. Like a stretched sheet of rubber, the surface tends to contract and resists being penetrated.

Why doesn't oil mix with water? (a) Nonpolar molecules repel water molecules. (b) Polar molecules repel nonpolar molecules. (c) Polar molecules attract one another. (d) Nonpolar molecules attract one another. Both (a) and (d).

(c) Polar molecules attract one another. Water molecules cling to one another and won't part to make room for uncharged (nonpolar) molecules. There's no repulsion.

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? 5% 5.0 M 105 M log (5) M 10- 5 M

10- 5 M

Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface? Polar groups attract one another. Polar groups repel water. Nonpolar groups attract one another. Nonpolar groups repel water. All of the above.

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 isn't this insect drowning? It is difficult to change the temperature of water. The insect is very light. Surface tension. The insect is swimming. The insect is flying just above the water surface.

Surface tension. The high surface tension of water allows the insect to remain on the surface.

What conditions must be met in order for an aqueous solution to be called "neutral"? The concentrations of hydronium and hydroxide ions are equal. The hydroxide ion concentration is greater than the hydronium ion concentration. There are no hydronium or hydroxide ions present in the solution. The hydronium ion concentration is greater than the hydroxide ion concentration. None of the above.

The concentrations of hydronium and hydroxide ions are equal.

How does the pH of the solution on the right compare with that of the solution on the left? Both of these solutions are equally basic. The solution on the right is acidic relative to the solution on the left. Both of these solutions are equally acidic. The solution on the right is basic relative to the solution on the left. The solution on the right is neutral relative to the solution on the left.

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

Despite its cohesion, water can flow because ... hydrogen bonds are too weak to affect movements. hydrogen bonds break and re-form rapidly. hydrogen ions can move between molecules. many water molecules have no hydrogen bonds. None of the above.

hydrogen bonds break and re-form rapidly. There are always enough hydrogen bonds to hold the water together, but the bonds break and re-form rapidly, allowing molecules to move relative to one another.

In a neutral solution the concentration of _____. hydrogen ions is equal to the concentration of hydroxide ions water molecules is less than the concentration of hydroxide ions hydrogen ions is greater than the concentration of hydroxide ions water molecules is less than the concentration of hydrogen ions hydrogen ions is less than the concentration of hydroxide ions

hydrogen ions is equal to the concentration of hydroxide ions

What name is given to this molecule? methane glucose hydronium ion water hydroxide ion

hydronium ion

What is the charge on a hydroxide ion? 1- 1+ 0 2- 2+

1- A hydroxide ion is formed when a water molecule loses a hydrogen ion.

In a washing machine, the detergent raised the pH to 9.0. The concentration of OH- in the solution is ... 10-9 M 5 M 10-1 M 10-5 M Can't tell without more information.

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

A solution is aqueous if ... water is the solvent. it occurs in nature. water is a solute. it contains water. None of the above.

water is the solvent. That's the definition of "aqueous." Water is the solvent if the solution contains more water molecules than any other kind of molecule.

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. Both (a) and (b). Both (b) and (c).

(a) A water molecule can make 4 hydrogen bonds. When you heat water, much of the heat is used to break hydrogen bonds. Only the remaining heat can increase molecular motion, raising the temperature.

The open spaces in water's crystal structure make it possible for ... (a) aquatic life to exist at the North Pole. (b) water to have a low boiling point. (c) life to occur in hot springs. Both (b) and (c). (a), (b), and (c).

(a) aquatic life to exist at the North Pole.

A 1 M solution contains ... (a) one mole of solute per liter of solution. (b) one mole of solute per liter of water. (c) a one-to-one ratio of solute to solvent molecules. Both (b) and (c). None of the above.

(a) one mole of solute per liter of solution. To make the solution, you dissolve the solute in some solvent and then add more solvent to bring the volume up to a liter.

Which statement is true of water's tensile strength? (a) It results from hydrogen bonding. (b) It helps to pull water through plants. (c) It involves both cohesion and adhesion. Both (a) and (b). (a), (b), and (c).

(a), (b), and (c). Because of hydrogen bonding, water coheres to itself and adheres to cell walls. That makes it possible to pull water through plants without breaking the water column.

Which factor is important in making it possible to cool yourself by sweating? Think carefully! (a) Molecules collide with varied angles and speeds. (b) Hydrogen bonds are relatively weak. (c) Water has more energy at the body surface. Both (a) and (b). (a), (b), and (c).

(a), (b), and (c). Random collisions allow some molecules to accumulate more energy than other molecules. The weakness of hydrogen bonds lets those molecules escape, leaving the cooler molecules behind.

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? (a) Wrong! Each atom makes one hydrogen bond, for a total of 3. (b) Right! Hydrogen bonds form at both ends of each covalent bond. (c) Wrong! Two hydrogen bonds are not in the plane of the atoms. None of the above. The student would say both (a) and (c).

(c) Wrong! Two hydrogen bonds are not in the plane of the atoms. The array of hydrogen bonds is three-dimensional.

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

Water has a high specific heat due to the hydrogen bonding between water molecules. Sulfuric acid is less resistant to temperature change than water. 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. Benzene is more resistant to temperature change than sulfuric acid.

Each water molecule is joined to _____ other water molecules by ____ bonds. two ... polar covalent three ... ionic four ... polar covalent four ... hydrogen two ... hydrogen

four ... hydrogen As can be seen in the illustration on page 1 of the activity titled "The Polarity of Water" a water molecule is joined to four other water molecules by hydrogen bonds.

Though you add heat, the temperature of boiling water remains constant because ... it takes energy to break covalent bonds. it takes energy to circulate water. water has a constant boiling temperature. it takes energy to break hydrogen bonds. None of the above. The temperature rises during boiling.

it takes energy to break hydrogen bonds. At boiling, all the added heat is used to break hydrogen bonds. Free of the water mass, the departing steam carries away all the added energy, with none left over to raise the temperature.