Practice questions (ch. 1 -3)

Question 1

Which of the following statements accurately describes the relationship between orbital radius and electron energy?
A) electrons are at higher energy levels closer to the nucleus
B) Valence electrons are at the lowest energy level
C) electrons are at a lower energy level closer to the nucleus

Answer 1

C) electrons are at a lower energy level closer to the nucleus

Question 2

What is the charge on a phosphate ion with 39 protons and 41 electrons?
A) 2+
B) 2-
C) Neutral

Answer 2

B) 2-

Question 3

What is the molecular formula of perchlorate?

Answer 3

ClO 4-

Question 4

What is the molecular formula of Ferrous chloride

Answer 4

FeCl2

Question 5

What is the molecular formula of Chlorite

Answer 5

ClO 2-

Question 6

What is the molecular formula of Sulfate

Answer 6

SO4 2-

Question 7

What is the molecular formula of Nitrite

Answer 7

NO2 -

Question 8

What is the molecular formula of Ferric chloride

Answer 8

FeCl3

Question 9

What happens when an electron moves from orbital n = 1 to orbital n = 3?

Answer 9

The electron becomes excited, absorbs energy

Question 10

Which of the following is true about the energy associated with an electron moving from orbital n = 3 to n = 6? (Note: R = 2.18 x 10-18 J)
A) 5 x 10^ -20 is absorbed
B)2 x 10^ -19 is emitted
C) 2 x 10 ^ -19 is absorbed

Answer 10

Rydberg formula

approximately 1.8 x 10^ -19

Question 11

True or false: The number of electrons that a given subshell can accommodate is dependent on the orbital the electron is in.

Answer 11

This statement is false. Each subshell can hold up to two electrons, regardless of the energy level, subshell shape, or subshell orientation.

Question 12

Which of the following orbitals can exist?
A) Orbital orientation -3 in a n=1 shell
B) Obrital orientation -6 in a n= 4 shell
C) orbital orientation -2 in a n = 3 shell

Answer 12

An n = 3 shell has an s subshell, a p subshell and a d subshell. The d subshell has 5 orbitals: -2, -1, 0, +1, +2. Therefore, it is possible to have a -2 orbital in a n = 3 shell.

Question 13

How many orbitals exist for a shell of n = 2?
A) 4
B) 9
C) 3

Answer 13

A shell of n = 2 is comprised of 0 to n-1 subshells (L). 2 - 1 = 1, so the subshells contained in an n = 2 shell are subshell L = 0 (s subshell) and L = 1 (p subshell). The s subshell contains a single orbital, 0. The p subshell contains 3 orbitals: -1, 0, +1. 1 orbital + 3 orbitals = 4 orbitals.

Question 14

Which of the following depicts the electron configuration of neutral fluorine?
A) 2p^5
B) 1s^2, 2s^2, 2p^5
C) 1s^2, 2s^2, 2p^6

Answer 14

The atomic number of fluorine is 9, which means there are 9 protons. Because we are talking about a neutral fluorine atom, there must also be 9 electrons. This electron configuration describes two electrons in the 1s subshell, two electrons in the 2s subshell, and five electrons in the 2p subshell

Question 15

What is the proper short-cut electron configuration for Li?

Answer 15

[He] 2s^1

Question 16

What is the proper short-cut electron configuration for Mg?

Answer 16

[Ne] 3s^2

Question 17

What is the proper short-cut electron configuration for Si?

Answer 17

[Ne] 3s^2, 3p^2

Question 18

What is the proper short-cut electron configuration for K?

Answer 18

[Ar] 4s1

Question 19

Which atom correctly matches following electron configuration: [Ar]4s^2, 3d^10, 4p^1?

Answer 19

Ga

Question 20

What is the correct electron configuration for the transition metal molybdenum (Mo)

Answer 20

[Kr] 5s^1, 4d^5
Exceptions to the classic rules of electron configuration stem from the idea that half-filled and fully-filled subshells are more stable than subshells filled with some other number of electrons.

Question 21

Which of the following elements are metalloids?
A) Boron
B) Aluminium
C) Silicon
D) Magnesium
E) Nickel

Answer 21

A) Boron

C) Silicon

Question 22

Alkali metals, when placed in water, are highly reactive and sometimes capable of causing large explosions. Which of the following properties of these metals serves as a cause of this reactivity?
A) alkaline metals have low electronegativity levels
B) They have high electron affinity
C) Alkali metals have low ionization energies

Answer 22

Members of the alkali metals have one valence electron. When this electron is lost, these elements gain a noble gas configuration, making them very stable. For this reason, alkali metals have very low ionization energies and lose an electron extremely easily, making them highly reactive in water. In this reaction, hydrogen gas is produced and the metal forms its corresponding oxide.

Question 23

True or false: Alkaline earth metals are more reactive than alkali metals because they have two valence electrons instead of one.

Answer 23

This statement is false. While alkaline earth metals do have two valence electrons instead of the one that alkali metals have, this makes them slightly less reactive, not more reactive.

Question 24

When elements from the chalcogen group form ions, what charge are they most likely to carry?
A) +2
B) -1
C) -2
D) +1

Answer 24

chalcogen valence shells need two more electrons to be filled, so these atoms typically become anions with a -2 charge.

Question 25

Is a halogen more likely to be reduced or oxidized, and why?

Answer 25

Halogens have seven valence electrons. To obtain a stable noble gas configuration, they must pick up an additional electron. When an element gains an electron, it is reduced.

Question 26

Why are noble gases unreactive in nature?

Answer 26

Noble gases are inert because they already possess a full, eight-electron valence shell. This configuration displays maximum stability.

Question 27

Rank the following elements in order of increasing atomic radius.
potassium, fluorine, boron, nitrogen, sodium.

Answer 27

Atomic radius decreases across a period and increases down a group, so larger atomic radii are found in the bottom left and the smaller atomic radii are found in the top right. Thus, the correct order in terms of increasing atomic radius is fluorine, then nitrogen, then boron, then sodium, and finally potassium.

Question 28

True or false: Ionization energy refers to the energy released when an element loses a valence electron.

Answer 28

This statement is false. Ionization energy refers to the energy required to free a valence electron from an element.

Question 29

Rank the following elements in order of increasing first ionization energy.
magnesium, sodium, chlorine, and sulfur

Answer 29

Ionization energy increases as you move across a period and decreases as you move down a group. Therefore, the correct order is sodium, then magnesium, then sulfur, and finally chlorine.

Question 30

Rank the following elements in order of increasing electron affinity
fluorine, chlorine, bromine, iodine,

Answer 30

Atoms closer to the top right of the periodic table have higher electron affinity values. Therefore, the correct order is iodine, then bromine, then chlorine, then fluorine.

Question 31

When more electronegative elements are in covalent bonds with less electronegative elements, the ______ density tends to be focused around the ______ electronegative of the two elements.

Answer 31

More electronegative elements tend to pull electron density toward themselves when participating in bonds.

Question 32

Rank the following elements in order of increasing electronegativity.
oxygen, carbon, lithium, fluorine, and sodium

Answer 32

Electronegativity increases from left to right across a period and decreases down a group; an easy way to remember this trend is to commit to memory that fluorine, near the top right of the table, is the most electronegative element. Therefore, the correct order is sodium, then lithium, then carbon, then oxygen, and finally fluorine.

Question 33

Adding an electron to a Cl atom would create

Answer 33

dding an electron to a Cl atom would create a negative charge; a negatively charged ion is known as an anion.

Question 34

Intermediates known as carbocations occur in many important organic reactions and involve a carbon atom with a positive charge. Based on this information, which of the following statements are likely true of carbocations? Select all that apply.
A) They do not satisfy octet rule
B) They are unstable
C) They are very likely to react with cations

Answer 34

A) Carbocations do not satisfy the octet rule, as they contain a positive charge.
B) Because carbocations do not satisfy the octet rule, they are highly unstable.

Question 35

True or false: H2SO4 is a polyatomic ion.

Answer 35

This statement is false. A polyatomic ion is a charged species consisting of multiple atoms bonded together. H2SO4 is not charged, and therefore cannot be a polyatomic ion (although note that its conjugate base, HSO4^-, is).

Question 36

An unknown substance is isolated from a previously undiscovered type of plant. The unknown substance is a reddish powdery solid at room temperature, soluble in water, and has a melting point of 204°C. What conclusion is most likely to be correct about this substance?
A) It lacks covalent bonds
B) It will be soluble in hexane
C) It is stabilized by ionic bonds

Answer 36

C
Ionic substances are generally solids at room temperature, have a high melting point, and are water-soluble, meaning that this substance is almost certainly stabilized by ionic bonds.

Question 37

Order the following bonds from most to least polar

N-H, O-H, C-H

Answer 37

carbon-hydrogen bonds are nonpolar, nitrogen-hydrogen bonds are moderately polar, and oxygen-hydrogen and fluorine-hydrogen bonds are highly polar. This is due to fluorine, oxygen, and nitrogen is the most electronegative elements. Thus, the order from most to least polar is O-H, N-H, C-H.

Question 38

True or false: Covalent bonds must involve two chemically distinct atoms sharing electrons with each other.

Answer 38

This statement is false. Covalent bonds can form between two atoms of the same element (e.g., O2) and a single atom can donate both electrons in coordinate covalent bonds

Question 39

In DNA, A-T base pairs involve two hydrogen bonds, whereas G-C pairs have three hydrogen bonds. Based on this, which of the following sequences would be most likely to be isolated from a single-cell organism living in very hot anaerobic conditions?

Answer 39

Hydrogen bonds are strong non-covalent intermolecular attractions that raise the melting and boiling points of a substance. As such, the DNA sequence with the most GC pairs would be expected to be the most heat-stable – and therefore, the most suitable to this environment. Of the answer choices, CCGATCGCTACG has the most C and G nucleotides.

Question 40

True or false: Ion-dipole interactions require a metal and a non-metal.

Answer 40

This statement is false. Ion-dipole interactions can take place between any ion and a dipole, not requiring a metal to be involved. Note that ion-dipole interactions are an intermolecular force; do not confuse them with ionic bonds, an intramolecular force that typically forms between a metal and non-metal.

Question 41

If a particular atom from the first two periods had 6 electrons in its valence shell, which orbitals would these electrons be distributed in?

Answer 41

S and P orbitals
All atoms with valence electrons will have some electrons in the s orbital, because this orbital fills first valence s orbital can hold two electrons, and from there, the remaining four electrons would occupy p orbitals.

Question 42

Which of the following elements has a completely-filled valence shell when it only has two valence electrons?
A) Xeon
B) Helium
C) Flourine

Answer 42

Helium has a maximum of two valence electrons.

Question 43

Which of the following atoms may be capable of having an expanded octet?
A) Phosphorus
B) Lithium
C) Boron
D) Sulfur

Answer 43

Phosphorus is capable of having an expanded octet, as in phosphorus pentafluoride, in which the central phosphorus has ten valence electrons
Sulfur is capable of having an expanded octet, as in sulfur hexafluoride, in which the central sulfur has twelve valence electrons.

Question 44

True or false: Free radicals are highly reactive because they have more electrons than their valence shells can hold stably.

Answer 44

This statement is false. Free radicals are compounds that have an odd number of valence electrons and so have an unpaired electron in their structure. This unpaired electron makes these compounds highly unstable.

Question 45

To carry a formal charge of 0, how many valence electrons should an atom of nitrogen have?

Answer 45

5
his can be determined from the periodic table. Nitrogen, according to its position on the table and its group number, should have 5 valence electrons.

Question 46

True or false: During an MCAT exam, the fastest way to determine an atom’s formal charge is by counting up the relative number of electrons and protons it contains

Answer 46

This statement is false. During a timed exam, formal charge should be calculated as the number of valence electrons an atom “should” have (according to the periodic table) and the number it actually has. Thus, formal charge can be quickly determined by counting the number of valence electrons and bonds made to other atoms.

Question 47

What is the molecular geometry of SO4^2-?

Answer 47

First, draw the Lewis structure of the sulfate anion. You will see that the central sulfur atom is doubly bound to two oxygen atoms, while the other two oxygens are connected by single bonds. As a result, the sulfur atom has four bonding groups and no lone pairs, yielding a tetrahedral geometry.

Question 48

What is the electronic geometry of water?

Answer 48

Water has two lone pairs and two single bonds,which makes its electronic geometry bent.

Question 49

Which bond angles can be found in PF5?

Answer 49

PF5 has five bonds and no lone pairs, so its molecular geometry is trigonal bipyramidal. In trigonal bipyramidal molecules, there are 90° and 120° bond angles

Question 50

True or false: Pi bonds have a small area of directly overlapping electron density, they form double bonds, and are stronger than sigma bonds.

Answer 50

False
In sigma bonds, there is a relatively large area of directly overlapping electron density compared to pi bonds, which occur between two parallel p orbitals and are weaker than sigma bonds. Single bonds between two atoms are made of sigma bonds, while double bonds are one sigma bond and one pi bond, and triple bonds are one sigma bond and two pi bonds. Therefore, double bonds are indeed stronger than single bonds, but that is because they have both a sigma bond component and a pi bond component. In a direct comparison, sigma bonds are stronger than pi bonds.

Question 51

Which of the seven reaction types is the following?

CaSO4 + 2 Na → Na2SO4 + Ca

Answer 51

Single displacement

Question 52

Which of the seven reaction types is the following?

2 NaCl + Ag2SO4 → 2 AgCl + Na2SO4

Answer 52

Double displacement

Question 53

During the combustion of 1 mole of sucrose (C12H22O11), how many moles of water will be produced?

Answer 53

The balanced equation for the combustion of sucrose is C12H22O11 + 12 O2 → 12 CO2 + 11 H2O

Question 54

In the following reaction which element is reduced?

Answer 54

Fe3+ is reduced to solid iron

Question 55

Write a balanced chemical equation for the single-displacement reaction of iron(II) nitrate and aluminum, which forms aluminum nitrate and solid iron.

Answer 55

3Fe(NO3)2 + 2 Al → 2Al(NO3)3 + 3 Fe

Question 56

Based on the reaction, how many molecules of product form when 5 molecules of barium nitrate completely react with 5 molecules of sulfuric acid?
Ba(NO3)2 + H2SO4 → BaSO4 + HNO3

Answer 56

This equation is not given in its balanced form. When we do balance it, we find that Ba(NO3)2 + H2SO4 → BaSO4 + 2 HNO3. In other words, for every mole of barium nitrate, three total moles of product will form (two moles of HNO3 and one mole of BaSO4). Thus, for every 5 moles of barium nitrate, 15 moles of product will be created.

Question 57

The reaction of magnesium sulfide with hydrogen peroxide produces both magnesium sulfate and water. What is the balanced equation for this process, and which element is reduced?

Answer 57

MgS + 4 H2O2 → MgSO4 + 4 H2O
On the reactant side, magnesium and sulfide ions have +2 and -2 charges, respectively. Magnesium maintains this +2 charge on the product side, while sulfur changes its oxidation state to +6. Oxygen, however, initially has an oxidation state of -1, but becomes -2 as a component of water. For this reason, oxygen, not magnesium, is reduced.

Question 58

True or false: The following equation shows a balanced chemical reaction:

Ag (s) + Fe(OH)2 (aq) → Ag (s) + Fe (s) + 2 OH-

Answer 58

This statement is false. While the atoms here are balanced (one silver, one iron, two oxygens, two hydrogens) on either side of the equation, the charges are not balanced. On the right, it should be 1 Ag2+ (aq) in order to balance the equation properly.

Question 59

What is the empirical formula of an unknown 60 g sample that contains roughly 40% carbon, 53% oxygen, and 7% hydrogen by mass?

Answer 59

To solve this question, the first step is to convert the mass percentages into mass values and then convert that ratio into a molar ratio. In a 60 g sample, 40% is 24 g, 53% is roughly 32 g, and 7% is roughly 4 g. Using the atomic mass of the elements in question, there are 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen. Thus, the ratio is 2:4:2 or 1:2:1 (CH2O).

Question 60

True or false: To derive a molecular formula, the atomic weight of each element and the percent composition by mass of each element is sufficient.

Answer 60

This statement is false. While this information is sufficient to calculate the ratio of each product (and thus the empirical formula), it is not sufficient to determine the actual molecular weight since only the ratio must be conserved. For example, an unknown compound could be C2H4 or C6H12 and still have an empirical ratio of CH2.

Question 61

What is the molecular formula of a molecule with an empirical formula CH and a molar mass of 130 g/mol?

Answer 61

To determine the molecular formula from the empirical formula and the molar mass, the most straightforward approach is to calculate the molar mass of the empirical formula and then divide the given molar mass by that value to determine how many of each element is needed. In this case, 1 carbon and 1 hydrogen combine to give a mass of 13 g/mol. 130 g/mol of our unknown / 13 g/mol = 10. So we must have 10 carbons and 10 hydrogens for a molecular formula of C10H10

Question 62

An unknown compound is found to contain roughly 26% carbon, 4% hydrogen, and 70% oxygen by mass. What is this compound’s empirical formula?

Answer 62

With percent composition questions, if not given a molar mass, it’s useful to imagine a 100 g sample of the compound and then use that to determine the ratio of elements. In a 100 g sample of this unknown, there are 26 g of carbon, 4 g of hydrogen, and 70 g of oxygen. Given carbon’s 12 g/mol atomic mass, there are 26/12 or just over two moles of carbon. In 4 g of hydrogen, there are 4 moles. In 70 g of oxygen, there are just over 4 moles of oxygen. Thus the ratio is roughly 2:4:4 or 1:2:2, giving an empirical formula of CH2O2.

Question 63

CH4 (g) + SO42- (aq) → H2O (l) + HS- (aq) + HCO3- (aq)
50 mg of methane and 60 mg of sulfate are mixed in a closed container. What is the limiting reagent, and how much excess reagent remains when that species has been exhausted?

Answer 63

To calculate the limiting reagent, we must use stoichiometry to determine how much sulfate is required to react with 50 mg of methane (or vice versa). However, we must first convert grams to moles. 0.05g CH4 x 1 mol / 16 g = 0.003 mol methane, which requires 0.003 mol SO42- , or 0.3 g, to fully react. Since we have only 0.06 g of SO42-, sulfate must be the limiting reagent. 0.06 g SO42- x 1 mol / 96 g = approximately 0.0006 mol, which reacts with 0.0006 mol, or 0.01 g, of CH4. We will thus have 0.04 g, or 40 mg, of methane in excess once the sulfate has been exhausted

Question 64

H3PO4 + Mg(OH)2 → H2O + Mg3(PO4)2
The student reacts exactly 2 moles of phosphoric acid with 6 moles of magnesium hydroxide. He measures 13.15 grams of magnesium phosphate (molar mass = 263 g/mol) produced. The limiting reagent is known to be phosphoric acid. What is the student’s percent yield?

Answer 64

The balanced reaction is 2 H3PO4 + 3 Mg(OH)2 → 6 H2O + Mg3(PO4)2. Theoretically, a complete reaction should yield 1 mol, or 263 g, magnesium phosphate. Percent yield can be calculated by taking (actual yield / theoretical yield) × 100% = (13.15 g / 263 g) × 100% = 5.0%.