Quiz 2: Atoms, Molecules, Properties of Water and pH

The structural formula for a certain molecule includes a group symbolized -O. The dash next to the oxygen atom means that a single bond exists to another atom, such as a carbon. Based on the valence of oxygen and the number of bonds it normally forms, what is the charge on the oxygen atom in this case?

-1

Fluorine has an atomic number of 9 and a mass number of 19. How many electrons are needed to complete the valence shell of a fluorine atom?

1

A pH of 7 is neutral due to the dissociation of water molecules in pure water. How many molecules of water have broken down into a hydroxide ion and a hydronium ion at pH 7?

1 in 10 million

Assume that acid rain has lowered the pH of a particular lake to pH 4.0. What is the hydroxyl ion concentration of this lake?

1 x 10-10 mol of hydroxyl ion per liter of lake water

One liter of a solution of pH 2 has how many more hydrogen ions (H+) than 1 L of a solution of pH 6?

10,000 times more

What is the hydroxide ion concentration of the lake described in question 7?

10-10 M

Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake?

10-4 M

A solution with a pH of 5 has how many more protons in it than a solution with a pH of 7?

100 times

One liter of a solution pH 9 has how many more hydroxyl ions (OH-) than 1 L of a solution of pH 4?

100,000 times more

The atomic number of each atom is given to the left of each of the elements below. Which of the atoms has the same valence as carbon

14silicon

From its atomic number of 15, it is possible to predict that the phosphorus atom has

15 protons and 15 electrons

An atom with an atomic number of 9 and a mass number of 19 would have an atomic mass of approximately

19 daltons

What is the maximum number of covalent bonds an element with atomic number 8 can make with hydrogen?

2

What is the maximum number of electrons in the 1s orbital of an atom?

2

What is the valence of an atom with six electrons in its outer electron shell?

2

Calcium has an atomic number of 20 and an atomic mass of 40. Therefore, a calcium atom must have

20 protons

What is the approximate atomic mass of an atom with 16 neutrons, 15 protons, and 15 electrons?

31 daltons

A molecule of carbon dioxide (CO2) is formed when one atom of carbon (atomic number 6) is covalently bonded with two atoms of oxygen (atomic number 8). What is the total number of electrons that must be shared between the carbon atom and the oxygen atoms in order to complete the outer electron shell of all three atoms?

4

At what temperature is water at its densest?

4°C

Which of the following statements is false? 1) Atoms of the various elements differ in their number of subatomic particles. 2) All atoms of a particular element have the same number of protons in their nuclei. 3) The neutrons and protons present in the nucleus of an atom are almost identical in mass; each has a mass of about 1 dalton. 4) An atom is the smallest unit of an element that still retains the properties of the element. 5) Protons and electrons are electrically charged particles. Protons have one unit of negative charge, and electrons have one unit of positive charge.

5) Protons and electrons are electrically charged particles. Protons have one unit of negative charge, and electrons have one unit of positive charge.

You have two beakers. One contains a solution of HCl at pH = 1.0. The other contains a solution of NaOH at pH = 13. Into a third beaker, you slowly and cautiously pour 20 mL of the HCL and 20 mL of the NaOH. After complete stirring, the pH of the mixture will be

7.0

Which of the following effects is produced by the high surface tension of water?

A water strider can walk across the surface of a small pond.

Which of the following is the best description of an atom's physical structure?

Atoms are little bubbles of space with mass concentrated at the center of the bubble.

Which of the following molecules is polar?

C3H7OH and C2H5COOH are polar molecules.

What is the difference between covalent bonds and ionic bonds?

Covalent bonds involve the sharing of electrons between atoms, and ionic bonds involve the electrical attraction between atoms.

Nitrogen (N) is much more electronegative than hydrogen (H). Which of the following statements is correct about the atoms in ammonia (NH3)?

Each hydrogen has a partial positive charge

Which of the following would be regarded as compounds?

H2O and CH4, but not H2 and O2

Which of the following ionizes completely in solution and is considered to be a strong acid?

HCl

Why does ice float in liquid water?

Hydrogen bonds stabilize and keep the molecules of ice farther apart than the water molecules of liquid water.

Which of the following is true of carbon?

It can form polar and nonpolar bonds

The atomic number of neon is 10. Therefore, which of the following is correct about an atom of neon?

It has 8 electrons in its outer electron shell. It is inert.

If an atom has a charge of +1, which of the following must be true?

It has one more proton than it does electrons.

Which of the following is a property of liquid water?

Its heat of vaporization is higher than that for most other substances.

Which of the following statements is completely correct?

NH3 is a weak base (alkali), and HCl is a strong acid.

In ammonium chloride salt (NH4Cl) the anion is a single chloride ion, Cl-. What is the cation of NH4Cl?

NH4 with a charge of +1

You have two beakers; one contains pure water, the other contains pure methanol (wood alcohol). The covalent bonds of methanol molecules are nonpolar, so there are no hydrogen bonds among methanol molecules. You pour crystals of table salt (NaCl) into each beaker. Predict what will happen.

NaCl crystals will dissolve readily in water but will not dissolve in methanol.

Which of the following ionizes completely in solution and is considered to be a strong base (alkali)?

NaOH

Do all human body fluids have the same pH? If not, rank, in the order of low to high, the pH of blood, urine, and stomach acid.

No. The pH ranking from low to high is stomach acid, urine, blood.

Consider two solutions: solution X has a pH of 4; solution Y has a pH of 7. From this information, we can reasonably conclude that

None of the other answer choices correctly describes these solutions.

Which of the following true statements can be attributed to water's high specific heat?

Our body temperature can take a long time to passively change because it is composed mostly of water.

Which statement is true of all atoms that are anions?

The atom has more electrons than protons

What holds electrons in a covalent bond?

The negative charges on the electrons are attracted by the positive charges on both nuclei.

The nucleus of a nitrogen atom contains 7 neutrons and 7 protons. Which of the following is a correct statement concerning nitrogen?

The nitrogen atom has a mass number of 14 and an atomic mass of approximately 14 daltons.

Silicon's atomic number is 14; in the periodic table it is directly beneath carbon. Silicon is abundant in the Earth's crust, yet, unlike C, N, O, and H, silicon is not a common element in organisms. What about the atomic structure of silicon probably accounts for this?

The nucleus of silicon is probably too big to form long chains of Si-Si molecules (analogous to long chains of carbon molecules).

The cities of Portland, Oregon, and Minneapolis, Minnesota, are at about the same latitude, but Minneapolis has much hotter summers and much colder winters than Portland does. Why? (Portland is near the Pacific Ocean; Minneapolis is near a number of large lakes.)

The ocean is so large that it has a highly moderating influence on temperature.

A 100 mL beaker contains 10 mL of NaOH solution at pH = 13. A technician carefully pours into the beaker, 10 mL of HCl at pH = 1. Which of the following statements correctly describes the results of this mixing?

The pH of the beaker's contents falls.

Which of the following statements is true about buffer solutions?

They maintain a relatively constant pH when either acids or bases are added to them.

Three or four of the following statements are true and correct. Which one, if any, is false? If all the statements are true, choose answer E. 1) Carbon, hydrogen, oxygen, and nitrogen make up approximately 96% of living matter. 2) The trace element iodine is required only in very small quantities by vertebrates. 3) Virtually all organisms require the same elements in the same quantities. 4) Iron is an example of an element needed by all organisms. 5) All of the other statements are true and correct.

Virtually all organisms require the same elements in the same quantities

Which of the following is not considered to be a weak molecular interaction?

a covalent bond

Sometimes atoms form molecules by sharing two pairs of valence electrons. When this occurs, the atoms are said to be joined by

a double covalent bond

When the atoms involved in a covalent bond have the same electronegativity, what type of bond results?

a nonpolar covalent bond

What results from an unequal sharing of electrons between atoms?

a polar covalent bond

Water's high specific heat is mainly a consequence of the

absorption and release of heat when hydrogen bonds break and form.

A given solution contains 0.0001(10-4) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?

acidic: H+ donor

Elements found on the left side of the periodic table contain outer shells that are _____; these elements tend to form _____ in solution.

almost empty; cations

Oxygen has an atomic number of 8 and a mass number of 16. Thus, the atomic mass of an oxygen atom is

approximately 16 daltons

Each element is unique and different from other elements because of the number of protons in the nuclei of its atoms. Which of the following indicates the number of protons in an atom's nucleus?

atomic number

Atoms whose outer electron shells contain eight electrons tend to

be stable and chemically nonreactive, or inert

About 25 of the 92 natural elements are known to be essential to life. Which four of these 25 elements make up approximately 96% of living matter?

carbon, hydrogen, nitrogen, oxygen

The ionic bond of sodium chloride is formed when

chlorine gains an electron from sodium

If the pH of a solution is decreased from 9 to 8, it means that the

concentration of H+ has increased 10-fold (10X) compared to what it was at pH 9 and concentration of OH- has decreased to one-tenth (1/10) what it was at pH 9.

If the pH of a solution is increased from pH 5 to pH 7, it means that the

concentration of OH- is 100 times greater than what it was at pH 5.

Buffers are substances that help resist shifts in pH by

donating H+ to a solution when they have been depleted and accepting H+ when the are in excess.

How many electrons are involved in a double covalent bond?

four

Which of the following solutions has the greatest concentration of hydrogen ions [H+]?

gastric juice at pH 2

Which of the following molecules contains the strongest polar covalent bond?

h2o

Water has a high specific heat because of the _____.

hydrogen bond formed between the hydrogen of one water molecule and the oxygen of another water molecule

What gives rise to the cohesiveness of water molecules?

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

Trace elements are those required by an organism in only minute quantities. Which of the following is a trace element that is required by humans and other vertebrates?

iodine

Which of the following results from a transfer of electron(s) between atoms?

ionic bond

A solution contains 0.0000001(10-7) moles of hydroxyl ions [OH-] per liter. Which of the following best describes this solution?

neutral

When two atoms are equally electronegative, they will interact to form

nonpolar covalent bonds

Hydrophobic substances such as vegetable oil are

nonpolar substances that repel water molecules.

A covalent bond is likely to be polar when

one of the atoms sharing electrons is much more electronegative than the other atom.

A covalent chemical bond is one in which

outer-shell electrons of two atoms are shared so as to satisfactorily fill the outer electron shells of both atoms.

What is the pH of a solution with a hydroxyl ion [OH-] concentration of 10-12 M?

pH 2

What is the pH of a solution with a hydrogen ion [H+] concentration of 10-8 M?

pH 8

In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by

polar covalent bonds

The mass number of an element can be easily approximated by adding together the number of __________ in an atom of that element.

protons and neutrons

Which of the following solutions has the greatest concentration of hydroxyl ions [OH-]?

seawater at pH 8

An atom has four electrons in its valence shell. What types of covalent bonds is it capable of forming?

single, double, or triple

While water has many exceptional and useful properties, which is the rarest property among compounds?

solid water is less dense than liquid water

To act as an effective coolant in a car's radiator, a substance has to be a liquid at the temperatures found in your car's engine and have the capacity to absorb a great deal of heat. You have a reference book with tables listing the physical properties of many liquids. In choosing a coolant for your car, which table would you check first?

specific heat

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

Pure, freshly-distilled water has a pH of 7. This means that

the concentration of H+ ions in the water equals the concentration of OH- ions in the water.

In the term trace element, the modifier trace means

the element is required in very small amounts

The reactivity of an atom arises from

the existence of unpaired electrons in the valence shell.

Temperature usually increases when water condenses. Which behavior of water is most directly responsible for this phenomenon?

the release of heat by the formation of hydrogen bonds

An atom has six electrons in its valence shell. How many single covalent bonds would you expect it to form in most circumstances?

two

How many electrons are involved in a single covalent bond?

two

Research indicates that acid precipitation can damage living organisms by

washing away certain mineral ions that help buffer soil solution and are essential nutrients for plant growth.

When are atoms most stable?

when all of the electron orbitals in the valence shell are filled