[2] Practice Test Flashcards
There are __________ naturally occurring elements.
92
Which of the following is a trace element?
[A] nitrogen
[B] copper
[C] carbon
[D] oxygen
[E] hydrogen
Copper (Cu) is a trace element. Copper accounts for less than 0.01% of living matter.
What are the four most abundant elements found in living systems, making up 96%?
hydrogen, oxygen, nitrogen, carbon
If I added proton number and neutron number, what would be the result?
atomic mass number
Which of the subatomic particles, as its name implies, is electrically neutral?
neutrons
The number of protons in an uncharged atom __________.
equal the number of electrons
Consider a hypothetical atom with an atomic number of 4 and an atomic mass of 9.0. How many neutrons does this atom have?
5
An uncharged atom of nitrogen (atomic number = 7) has __________.
seven protons, and seven electrons
Isotopes of an element will always differ in __________.
atomic mass
A particular carbon isotope has an atomic number of 6 and an atomic mass of 14. The respective number of neutrons, protons, and electrons that this carbon isotope has is __________.
8 neutrons
6 protons
6 electrons
Phosphorus-32 (radioactive) has __________ than phosphorus-35 (normal).
three fewer neutrons
The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium?
An atom with 20 protons, 21 neutrons, and 20 electrons
Radioactive isotopes are useful in scientific research because __________.
they can be used as tracers to follow particular atoms and molecules through metabolic pathways, especially in medicine
Potassium (atomic number 19, mass number 40) and sodium (atomic number 11, mass number 23) have similar chemical properties and reactive behavior. This is because uncharged atoms of potassium and sodium __________.
have different mass numbers and each has one electron in its outermost electron shell
The chemical characteristics or reactivity of an element depend mostly on the __________.
number of electrons in its outermost shell
Some groups of elements react chemically in similar ways. For example, the chemistry of sodium and the chemistry of lithium are similar. The chemistry of chlorine and the chemistry of iodine are also similar. These similarities in chemistry result when different elements have similar __________.
numbers of outer-shell electrons
How many electrons would be present in the valence shell of a sulfur atom (atomic number 16, mass number 32)?
6
For most atoms, a stable configuration of electrons is attained when the atom __________.
has a full number electrons in its outermost shell
An atom that normally has __________ in its outer shell would not tend to form chemical bonds with other atoms.
eight electrons
When one or more pairs of valence electrons are shared by two neutral atoms, what type of bond is formed?
a covalent bond
A polar covalent bond is a bond that __________.
the electrons of the bond are not shared equally
A covalent bond is likely to be polar if __________.
one of the atoms sharing electrons is much more electronegative
When two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner, the two resulting oppositely charged atoms (or molecules)____________.
are ions
A sodium atom has a mass number of 23. Its atomic number is 11. How many electrons does it have if it is not an ion?
11
Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons?
The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge.
The compound CaSO4 ionizes into a calcium ion and a sulfate ion (SO4). Calcium has two electrons in its outer shell. Upon ionization, what would you expect the charge on the sulfate ion to be?
-2
Ionic bonds form as a result of __________.
attraction between ions that have opposite charges
A hydrogen bond __________.
is a weak chemical bond
What is the role of van der Waals interactions in biological molecules?
Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules.
Which of the following molecules has the shape of a completed tetrahedron?
methane (CH4)
Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application?
the molecule’s shape
Which of the following statements is true about chemical reactions?
[A] Only inorganic molecules can participate in chemical reactions.
[B] They represent the way matter is created and destroyed.
[C] They involve the making and breaking of chemical bonds, leading to changes in the composition of matter.
[D] They reach chemical equilibrium when the amounts of products and reactants are equal.
[E] They may have different numbers of a given atom on each side of the equation arrow.
[C] They involve the making and breaking of chemical bonds, leading to changes in the composition of matter.
Which of the following statements describes a reversible reaction that has reached chemical equilibrium?
[A] The rate of the reverse reaction exceeds the rate of the forward reaction.
[B] The rate of the reverse reaction equals the rate of the forward reaction.
[C] The forward and the reverse reactions have stopped.
[D] The rate of the forward reaction exceeds the rate of the reverse reaction.
[E] The concentration of the reactants is equal to the concentration of the products.
[B] The rate of the reverse reaction equals the rate of the forward reaction.
Cells are surrounded by water, and cells themselves consist of about 70- 95% water. Which of the following choices best describe the result?
[A] Dissolved substances can be easily transported within a cell or between cells in multicellular organisms.
[B] A variety of nutrient molecules is readily available as dissolved solutes.
[C] Waste products produced by cell metabolism can be easily removed.
[D] The temperature of living things tends to change relatively slowly.
[E] All of the listed responses are correct.
[E] All of the listed responses are correct.
Water is a polar molecule. This means that __________.
the opposite ends of the molecule have opposite electrical charges
The partial charges on a water molecule occur because of __________.
the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule
In a group of water molecules, hydrogen bonds form between __________.
the oxygen atom in one water molecule and a hydrogen atom in another water molecule
If water were NOT a polar molecule, how would the effects of global warming differ from what are 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.
The tendency of water molecules to stay close to each other as a result of hydrogen bonding __________.
[A] provides the surface tension that allows leaves to float on water
[B] keeps water moving through the vessels in a tree trunk
[C] acts to moderate temperature
[D] is called cohesion
[E] All of the listed responses are correct.
[E] All of the listed responses are correct.
What do cohesion, surface tension, and adhesion have in common with reference to water?
All are properties related to hydrogen bonding.
Most of water’s unique features (for example, its versatility as a solvent, ability to moderate temperature, and cohesive behavior) result from the fact that __________.
oxygen attracts electrons more than hydrogen does
The ability of water molecules to form hydrogen bonds with other water molecules and water’s ability to dissolve substances that have charges or partial charges are __________.
both caused by water’s partial charges
Adhesion is best described as __________.
the clinging of one substance to another substance
You can fill a glass of water to just slightly above the rim without it spilling over the glass. What property of water best explains this phenomenon?
surface tension
Which action would involve the greatest transfer of heat?
[A] evaporating 1 g of water at 25 degrees C
[B] cooling 10 g of water from 80 degrees C to 40 degrees C
[C] raising the temperature of 10 g of ethyl alcohol by 25 degrees C
[D] condensing 5 g of steam to liquid water
[E] changing the temperature of 1 g of water from 10 degrees C to 90 degrees C
[D] condensing 5 g of steam to liquid water
Imagine that organisms consisted of 70-95% alcohol instead of 70-95% water. Alcohol’s specific heat is about half that of water. How would living things be different?
Systems for temperature regulation would have to be much more efficient.
The amount of heat required to change the temperature of 1 g of any substance by one degree C is defined as __________.
the specific heat of that substance
The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as __________.
the heat of vaporization of that substance
The reason that coastal climates are more moderate than inland climates is due primarily to water’s high __________.
specific heat
Sweating has a cooling effect because of water’s high __________.
heat of vaporization
Because molecules of water are farther apart in ice than in liquid water, __________.
ice floats
Water is a very versatile solvent because water molecules are __________.
polar
How does the polarity of water contribute to its ability to dissolve so many substances?
Because it is polar, water’s oppositely charged ends are attracted to positively and negatively charged ions and molecules. Water molecules form a hydration shell around oppositely charged particles.
Nonpolar molecules that cluster away from water molecules are called __________ molecules.
hydrophobic
A molecule that has all nonpolar covalent bonds would be __________.
hydrophobic
Hydrophobic molecules are __________ water.
repelled by
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.
Hydrophilic substances, but NOT hydrophobic substances, __________.
have charges and partial charges to which water molecules can adhere
Some substances, such as oil and gasoline, will NOT dissolve in water because __________.
their molecules have no charges or partial charges to which water molecules can adhere
A mole of ethyl alcohol weighs 46 g. How many grams of ethyl alcohol are needed to produce 1 L of a 2-millimolar (2 mM) solution?
0.092 g
An acid is ___.
a compound that donates hydrogen ions to a solution
Adding acid tends to __________ of a solution.
increase the hydrogen ion concentration and lower the pH
Which of the following dissociations is that of an acid?
[A] NaOH → Na+ + OH-
[B] HF → H+ + F-
[C] KOH → K++ OH-
[D] H2O → H+ + OH-
[E] NH3+ H+ → NH4+
[B] HF → H+ + F-
A glass of grapefruit juice, at pH 3, contains __________ H+ as a glass of tomato juice, at pH 4.
ten times as much
A solution at pH 6 contains __________ than the same amount of solution at pH 8.
100 times more H+
Adding a base tends to __________ of a solution.
lower the hydrogen ion concentration and increase the pH
When the pH of a solution shifts from 7 to 3, how has the hydrogen ion concentration changed?
It has increased by 10,000 times.
A substance that minimizes changes in the concentration of H+ and OH in a solution is a __________.
buffer
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-).
