Take The Ultimate Chemistry Exam Test!
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Questions and Answers
- 1.
Which one of the following is most likely to be an ionic compound?
- A.
CH4
- B.
O2
- C.
CaCl2
- D.
NH3
Correct Answer
C. CaCl2Explanation
CaCl2 is most likely to be an ionic compound because it consists of a metal (Ca) and a non-metal (Cl). Ionic compounds are formed when a metal transfers electrons to a non-metal, resulting in the formation of positive and negative ions that are held together by electrostatic forces. In CaCl2, calcium (Ca) donates two electrons to each chlorine (Cl) atom, resulting in the formation of Ca2+ and Cl- ions. These ions attract each other, forming an ionic bond and creating the compound CaCl2.Rate this question:
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- 2.
Which of the following compounds has the greatest lattice energy?
- A.
KBr
- B.
KCl
- C.
KI
- D.
KF
Correct Answer
D. KFExplanation
KF has the greatest lattice energy among the given compounds. Lattice energy is the energy released when gaseous ions combine to form a solid ionic compound. It is directly proportional to the charges of the ions and inversely proportional to the distance between them. In this case, all the compounds have the same cation (K+) but different anions (Br-, Cl-, I-, F-). As the size of the anion decreases, the distance between the ions decreases, leading to a stronger attraction and higher lattice energy. F- is the smallest anion, resulting in the strongest attraction and therefore the highest lattice energy.Rate this question:
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- 3.
Based on the tendency of atoms to gain or lose electrons to fulfill the octet rule, which of the following ions has an incorrect charge?
- A.
Na+
- B.
O2-
- C.
Ca2-
- D.
Cl-
Correct Answer
C. Ca2-Explanation
The octet rule states that atoms tend to gain or lose electrons in order to achieve a stable electron configuration with a full outer shell of electrons, typically containing 8 electrons. Na+ has a charge of +1 because it loses one electron, O2- has a charge of -2 because it gains two electrons, and Cl- has a charge of -1 because it gains one electron. However, Ca2- has an incorrect charge because calcium (Ca) typically loses two electrons to achieve a stable electron configuration, resulting in a charge of +2. Therefore, the correct charge for calcium ion should be Ca2+.Rate this question:
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- 4.
Which of the following diatomic molecules has the longest bond length?
- A.
N==N
- B.
Br-Br
- C.
F-F
- D.
O==O
Correct Answer
B. Br-BrExplanation
The correct answer is Br-Br. This is because bromine (Br) is a larger atom compared to nitrogen (N), oxygen (O), and fluorine (F). As a result, the bond length in Br-Br is longer because the larger atoms have more electron-electron repulsion, causing the bond to stretch and become longer. In diatomic molecules, the bond length generally increases as the size of the atoms involved increases.Rate this question:
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- 5.
The measure of an atoms ability to attract electrons towards itself in a chemical bond is known as?
- A.
Electronegativity
- B.
Bond strength
- C.
Electron affinity
- D.
Bond order
Correct Answer
A. ElectronegativityExplanation
Electronegativity is the measure of an atom's ability to attract electrons towards itself in a chemical bond. It indicates the strength of the atom's pull on the shared electrons. Bond strength refers to the energy required to break a chemical bond, while electron affinity is the energy change that occurs when an atom gains an electron. Bond order, on the other hand, is a measure of the number of chemical bonds between two atoms. Therefore, the correct answer is electronegativity.Rate this question:
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- 6.
Which of the following compounds has the greatest bond polarity?
- A.
Cl-Br
- B.
Cl-Cl
- C.
NH3
- D.
H-F
Correct Answer
D. H-FExplanation
H-F has the greatest bond polarity among the given compounds. Bond polarity is determined by the difference in electronegativity between the two atoms in the bond. Fluorine (F) has the highest electronegativity value of all the elements, while hydrogen (H) has a relatively low electronegativity value. The large electronegativity difference between H and F in H-F results in a highly polar covalent bond, with the electron density being pulled towards the electronegative fluorine atom. This creates a significant separation of charge and a strong dipole moment, making H-F the compound with the greatest bond polarity.Rate this question:
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- 7.
Calculate the oxidation number of the nitrogen atom in NH3.
- A.
0
- B.
+1
- C.
-1
- D.
-3
Correct Answer
D. -3Explanation
The oxidation number of an atom is the charge it would have in a compound if electrons were transferred completely. In NH3, hydrogen has an oxidation number of +1 since it usually loses its electron and nitrogen has an oxidation number of -3 since it usually gains three electrons to complete its octet. Therefore, the correct answer is -3.Rate this question:
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- 8.
Which metal would most likely have the highest melting point?
- A.
Li
- B.
Na
- C.
Ca
- D.
K
Correct Answer
C. CaExplanation
Calcium (Ca) would most likely have the highest melting point among the given metals. This is because calcium has a higher atomic number and a stronger metallic bond compared to the other metals listed. The stronger metallic bond requires more energy to break, resulting in a higher melting point.Rate this question:
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- 9.
Which bond type best describes the type of bond that will form between O and H?
- A.
Nonpolar convalent
- B.
Mostly ionic
- C.
Mostly covalent
- D.
Polar covalent
Correct Answer
D. Polar covalentExplanation
The bond that will form between O and H is a polar covalent bond. This is because oxygen is more electronegative than hydrogen, meaning that it has a stronger pull on the shared electrons. As a result, the electrons in the bond will spend more time around the oxygen atom, giving it a partial negative charge, while the hydrogen atom will have a partial positive charge.Rate this question:
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- 10.
Based on your knowledge of bond energy, which of the following compounds would release the most energy during combustion?
- A.
CH4
- B.
C2H6
- C.
C3H8
- D.
C2OH6
Correct Answer
C. C3H8Explanation
C3H8, also known as propane, would release the most energy during combustion compared to the other compounds listed. This is because propane has more carbon and hydrogen atoms, which means it has more bonds that can be broken and reformed during combustion. The breaking of these bonds releases energy, and since propane has more bonds, it can release more energy.Rate this question:
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- 11.
Use VSEPR theory to predict the geometry of the SF6 molecule.
- A.
T-shaped
- B.
Trigonal bipyramidal
- C.
Tetrahedral
- D.
Octaheadral
Correct Answer
D. OctaheadralExplanation
The SF6 molecule consists of one sulfur atom bonded to six fluorine atoms. According to the VSEPR theory, the sulfur atom has six electron pairs around it, resulting in an octahedral geometry. In an octahedral geometry, the central atom is surrounded by six bonded atoms or lone pairs, arranged symmetrically in a three-dimensional shape resembling two square pyramids joined at the base. Therefore, the correct answer is octahedral.Rate this question:
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- 12.
The bond angles found in a molecule with AX5 geometry are?
- A.
90 degrees
- B.
120 degrees
- C.
90 and 120 degrees
- D.
109.5 degrees
Correct Answer
C. 90 and 120 degreesExplanation
In a molecule with AX5 geometry, there are five bonding pairs of electrons around the central atom. These bonding pairs repel each other, causing the molecule to adopt a trigonal bipyramidal shape. The bond angles in this geometry are 90 degrees between the equatorial positions and 120 degrees between the axial and equatorial positions. Therefore, the correct answer is 90 and 120 degrees.Rate this question:
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- 13.
Which of the following bonds has the most ionic character
- A.
C-H
- B.
H-F
- C.
Na-I
- D.
K-F
Correct Answer
D. K-FExplanation
The bond between K and F has the most ionic character. This is because potassium (K) is a metal and fluorine (F) is a non-metal. Metals tend to lose electrons and become positively charged ions, while non-metals tend to gain electrons and become negatively charged ions. In the case of K-F, potassium loses an electron to become K+ and fluorine gains an electron to become F-. This large difference in electronegativity between the two elements results in a highly polar bond with significant ionic character.Rate this question:
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- 14.
What is the CN bond order in H3CCN (assume all atoms obey the octet rule)?
- A.
-1
- B.
+1
- C.
0
- D.
+3
Correct Answer
D. +3Explanation
The CN bond order in H3CCN is +3. Bond order is a measure of the number of chemical bonds between two atoms. In this case, the CN bond in H3CCN is a triple bond, consisting of three chemical bonds. Therefore, the bond order is +3.Rate this question:
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- 15.
What is the formal charge on the nitrogen in hydroxylamine, H2NOH?
- A.
-1
- B.
0
- C.
+1
- D.
+5
Correct Answer
B. 0Explanation
The formal charge on an atom can be calculated by subtracting the number of lone pair electrons and half of the bonding electrons from the number of valence electrons. In the case of hydroxylamine, nitrogen has 5 valence electrons and is bonded to one hydrogen atom and one oxygen atom, which contribute a total of 4 electrons. Nitrogen also has one lone pair of electrons. Therefore, the formal charge on nitrogen can be calculated as 5 - 4 - 2 = -1. However, in the given options, the correct answer is 0, which means that the question might be incomplete or there may be some other factors that need to be considered.Rate this question:
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- 16.
Which of the following has the smallest bond angles?
- A.
CO2
- B.
NH3
- C.
SO3
- D.
XeF4
Correct Answer
D. XeF4Explanation
XeF4 has the smallest bond angles among the given options. This is because XeF4 adopts a square planar molecular geometry, where the four fluorine atoms are arranged symmetrically around the central xenon atom. The repulsion between the electron pairs in the outer shell of xenon causes the bond angles to be smaller compared to the other molecules. In contrast, CO2 has linear geometry with a bond angle of 180 degrees, NH3 has a trigonal pyramidal geometry with a bond angle of 107 degrees, and SO3 has a trigonal planar geometry with a bond angle of 120 degrees.Rate this question:
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- 17.
Which molecule has no dipole moment?
- A.
BrF3
- B.
SO2
- C.
XeBr4
- D.
H2O
Correct Answer
C. XeBr4Explanation
XeBr4 has no dipole moment because it is a symmetrical molecule with a square planar geometry. The four Br atoms are arranged symmetrically around the central Xe atom, resulting in the cancellation of dipole moments. Therefore, the molecule as a whole has no net dipole moment.Rate this question:
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- 18.
Which of the following molecules is linear?
- A.
NH3
- B.
H2O
- C.
H2S
- D.
CO2
Correct Answer
D. CO2Explanation
CO2 is the correct answer because it is a linear molecule. It consists of two oxygen atoms bonded to a central carbon atom, with the carbon-oxygen double bond and the two carbon-oxygen single bonds arranged in a straight line. The molecule has a linear geometry, with a bond angle of 180 degrees. In contrast, NH3, H2O, and H2S are all non-linear molecules due to the presence of lone pairs on the central atom, causing a distortion in their geometries.Rate this question:
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- 19.
Which of the following statements is true of methane, CH4?
- A.
It is a tetrahedral molecule
- B.
It is a polar molecule
- C.
It contains single and double bonds
- D.
It contains 60% nitrogen by weight
Correct Answer
A. It is a tetrahedral moleculeExplanation
Methane, CH4, is a tetrahedral molecule. This means that it has a central carbon atom bonded to four hydrogen atoms, arranged in a three-dimensional shape resembling a pyramid with a triangular base. The four hydrogen atoms are positioned at the four corners of the tetrahedron, resulting in a symmetrical distribution of electron density around the carbon atom. This arrangement gives methane its tetrahedral shape and makes it a nonpolar molecule, as the electronegativity difference between carbon and hydrogen is negligible.Rate this question:
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- 20.
Using the bond energies, calculate the enthalpy change for the following combustion reaction.
- A.
-92 kJ/mol
- B.
+921 kJ/mol
- C.
-621 kJ/mol
- D.
+621 kJ/mol
Correct Answer
A. -92 kJ/molExplanation
delta H degrees=[4(C-H)+(C=C)+(Br-Br)]-[4(C-H)+(C-C)+2(C-Br)]
=(4x413+614+193)-(4x413+347+2x276)
=2459-2551=-92 kJ/molRate this question:
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- 21.
In the Lewis structure of nitrogen dioxide, NO2, how many pairs of electrons are bonding and how many are non-bonding?
- A.
5 pairs bonding, 4 pairs non-bonding
- B.
3 pairs bonding, 4 pairs non-bonding
- C.
4 pairs bonding, 4 pairs non-bonding
- D.
2 pairs bonding, 2 pairs non-bonding
Correct Answer
C. 4 pairs bonding, 4 pairs non-bondingExplanation
In the Lewis structure of nitrogen dioxide (NO2), there are a total of 8 valence electrons. To form stable bonds, nitrogen forms a double bond with one oxygen atom, which accounts for 4 bonding electrons. The remaining 4 valence electrons are non-bonding pairs, with each oxygen atom having one lone pair. Therefore, there are 4 pairs of electrons involved in bonding and 4 pairs of electrons that are non-bonding.Rate this question:
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- 22.
Indicate the molecular geometry and the net dipole moment of H3CF
- A.
Tetrahedral, AX4; net dipole moment arrow pointing to the right
- B.
Pyramidal; net dipole moment arrow point to the left
- C.
Bent; net dipole moment arrow pointing to the right
- D.
Planar tetrahedral; net dipole moment arrow pointing to the right
Correct Answer
A. Tetrahedral, AX4; net dipole moment arrow pointing to the rightExplanation
The molecule H3CF has a tetrahedral molecular geometry because it has four bonded atoms and no lone pairs of electrons on the central atom. The net dipole moment arrow pointing to the right indicates that the molecule is polar, with a greater electron density on the right side of the molecule. This is likely due to the electronegativity difference between the carbon and fluorine atoms, causing a partial negative charge on the fluorine atom and a partial positive charge on the carbon atom.Rate this question:
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- 23.
Briefly explain why Co2 is non-polar and OCS is polar.
- A.
CO2; O==C==O no dipole moment, cancels each out; OCS; O==C==S, contains a dipole moment,does not cancel each out
- B.
CO2 O==C==O contains a dipole moment, does not cancel each other out; OCS O==C==) no dipole moment, cancel each out
Correct Answer
A. CO2; O==C==O no dipole moment, cancels each out; OCS; O==C==S, contains a dipole moment,does not cancel each outExplanation
Co2 is non-polar because it has a linear molecular geometry and the two oxygen atoms are symmetrical with equal electronegativity. This results in the dipole moments of the two oxygen-carbon bonds canceling each other out, resulting in a molecule with no overall dipole moment. On the other hand, OCS is polar because it has a bent molecular geometry and the oxygen and sulfur atoms have different electronegativities. This creates a dipole moment, as the oxygen atom pulls the electron density towards itself more than the sulfur atom, resulting in an overall dipole moment for the molecule.Rate this question:
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Nov 16, 2023Quiz Edited by
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Dec 10, 2007Quiz Created by
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