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Quiz Session - Attempts With Random Questions

College Chemistry Exam Questions

Page 4 of 25

61.

According to Dalton’s Law of Partial Pressures:

  • The molecules of a gas exert the same pressure in a mixture as if they were not in a mixture

  • All gas molecules in a mixture exert the same amount of pressure

  • All gas species in a mixture contribute equally to the total pressure of that mixture

  • Some gas species always contribute more to pressure than do other species

  • There is no relationship between a gas’s pressure when that gas is isolated versus when it is mixed with other gases

Correct answer: The molecules of a gas exert the same pressure in a mixture as if they were not in a mixture

In other words, you can find the total pressure of a mixed gas by summing up the pressures exerted by each species within the gas. For example, if you have 1atm nitrogen gas in a container and you add 1atm oxygen gas from a separate container with the same volume, your total pressure will now be 2 atm.

62.

Write the acid ionization constant, Ka, for the following generic acid dissociation:

HA(aq) ⇌ A−(aq) + H+(aq)

  • Ka = ([A-][H+]) / [HA]

  • Ka = [HA] / ([A-][H+])

  • Ka = ([A-] + [H+]) / [HA]

  • Ka =  [HA] / ([A-] - [H+])

  • Ka = [A-]/[HA]

Correct answer: Ka = ([A-][H+]) / [HA]

The acid ionization constant is very similar to the ordinary equilibrium constant, Keq. It represents the ratio of products (in this case, the dissociated acid) to reactants (the undissociated acid). A larger Ka represents a stronger acid.

63.

All of the following are crystal lattice structures, except:

  • Trigonal planar

  • Cubic

  • Triclinic

  • Hexagonal

  • Tetragonal

Correct answer: Trigonal planar

Trigonal planar is a molecular geometry (e.g., in BF3) but is not found in crystal lattice structures.

The other answers are all real, common lattice structures. For example, water (H2O) freezes with a hexagonal lattice that gives solid water some interesting properties.

64.

cis-Pt(NH3)2Cl2 and trans-Pt(NH3)2Cl2 are examples of:

  • Geometric isomers

  • Structural isomers

  • Mirror images

  • Macromolecular substances

  • Isotopes

Correct answer: Geometric isomers

Both cis and trans forms have the same connectivity between atoms: Pt is the central atom, with two Cl atoms and two NH3 molecules connected to it. However, their spatial arrangement differs. In the cis form, both Cl atoms are on one side while both molecules NH3 are on the other. In the trans form, the atoms alternate instead.

65.

Which atoms undergo a change in oxidation state?

MnO2 + 4H+ + 2Cl-   → Mn2+ + 2H2O + Cl2

  • Mn, Cl

  • Mn, O

  • H, Mn

  • O, Cl

  • Cl, H

Correct answer: Mn, Cl

Mn goes from +4 to +2 (reduced) while Cl goes from -1 to 0 (oxidized). H and O maintain their standard oxidation states of +1 and -2, respectively.

66.

As you move across a period, what do you expect to happen to atomic radius?

  • Radius decreases because there are more protons to exert nuclear force

  • Radius decreases because the atom is less polarizable and more dense

  • Radius stays about the same because the effect of additional protons cancels out the effect of additional electrons

  • Radius increases because there are more electrons

  • Radius increases because there is increased electron shielding

Correct answer: Radius decreases because there are more protons to exert nuclear force

Though the atoms gain both protons and electrons, it turns out that the effect of one additional proton is greater than the effect of an additional electron in the same electron subshell. Therefore, atomic radius contracts across each period because the additional protons hold the electrons closer together.

67.

Which of the following is a base according to the Brønsted-Lowry definition but not the Arrhenius definition?

  • NH3

  • H2O

  • NaOH

  • KOH

  • Ca(OH)2

Correct answer: NH3

The Arrhenius definition requires bases to donate hydroxide ions in aqueous solution, while the Brønsted-Lowry definition requires bases to accept protons. NH3 obviously does not contain the OH- ion, but can gain a proton to become NH4+.

68.

What is the most concise name for HIO3?

  • Iodic acid

  • Hydroiodic acid

  • Iodine trioxic acid

  • Hydrogen triodic acid

  • Hydrogen iodine trioxide

Correct answer: Iodic acid

This is part of the oxyacid family, which is named by adding the suffix -ic to the defining element (in this case, iodine). Similarly, HBrO3 is bromic acid and H3PO4 is phosphoric acid. Since the hydrogens and oxygens are given, you need to name only the other element!

69.

What is it called when an organic molecule has two C=C double bonds separated by one C—C single bond, such that the entire chain looks like this: C=C—C=C?

  • Conjugation

  • Dialkylation

  • Alkyne

  • Benzene

  • Cyclic resonance

Correct answer: Conjugation

Double bonds alternating with single bonds are "conjugated," meaning that they can delocalize electrons over the entire span of the double bonds through resonance.

Benzene is a special kind of cyclic conjugated compound that can delocalize electrons over an entire ring.

70.

When balancing ionic equations, when should you add OH- (hydroxide) ions to balance out the H+ (protons) to form water?

  • When the reaction occurs in basic solution

  • When the reaction occurs in acidic solution

  • When spectating ions contain OH-

  • Always

  • Never

Correct answer: When the reaction occurs in basic solution

In basic solution, you can assume the presence of free hydroxide ions in solution. These would logically combine with protons to form water, so you can use them for the sake of balancing your equation. In contrast, acidic solutions have an abundance of protons, so you should assume that any protons you use to balance the equation will remain free in solution.

71.

In normal liquid chromatography, how are the phases constructed?

  • Polar stationary phase, non-polar mobile (liquid) phase

  • Non-polar stationary phase, polar mobile (liquid) phase

  • Both the stationary and mobile (liquid) phases are polar

  • Both the stationary and mobile (liquid) phases are non-polar

  • Both the stationary and mobile (liquid) phases have a mixture of polar and non-polar molecules

Correct answer: Polar stationary phase, non-polar mobile (liquid) phase

In general, chromatography separates molecules based on differential attractions to the stationary and mobile phases, so it would not make sense for the phases to be either both polar or both non-polar. The "normal" liquid chromatography has polar stationary (e.g., siloxane) and non-polar mobile. If the polarities are reversed, it is considered a "reversible" chromatography set-up.

72.

Is BrK a valid compound? Why or why not?

  • No, because it does not comply with standard nomenclature, but KBr would be valid

  • Yes, because the charges of the ions are balanced

  • No, because the charges are unbalanced, but Br2K would be valid

  • No, because the charges are unbalanced, but BrK2 would be valid

  • No, because Br and K differ substantially in electronegativity and would, therefore, form a covalent, not ionic, compound

Correct answer: No, because it does not comply with standard nomenclature, but KBr would be valid

Standard nomenclature dictates that the positively-charged ion (cation) be written firm, followed by the negatively-charged ion. In this case, K+ and Br- form an ionic bond. Ionic and covalent compounds are written according to the same rules; it is up to you to determine, based on the relative electronegativities, whether the bond is ionic or covalent in nature.

73.

What is the limiting reagent in the following reaction?

Pb(OH)4 + 2H2SO4 → Pb(SO4)2 + 4H2O

  • Impossible to tell

  • Pb(OH)4

  • H2SO4

  • Pb(SO4)2

  • H2O

Correct answer: Impossible to tell

The limiting reagent involves the actual quantities that you have of each substance, rather than any information you can glean from the equation itself.

74.

You have a buffer with pKa 4.8 and you add a small amount of a strong acid (pKa < 2). What do you expect will happen?

  • The solution's pH will decrease a little below 4.8

  • The solution's pH will not change

  • The solution's pH will increase a little above 4.8

  • The solution will change colors

  • The strong acid will not be soluble in this buffer

Correct answer: The solution's pH will decrease a little below 4.8

A buffer should be able to resist changes in pH, leading to a gradual decrease as more and more acid is added. As the buffer's conjugate base is depleted, the addition of strong acid will cause more precipitous changes in pH. No color change should be expected unless the buffer contains an indicator.

75.

What type(s) of reaction(s) is/are occurring in the following equation?

CH3OH + O2 → CO2 + H2O

i. Metathesis

ii. Combustion

iii. Precipitation

iv. Redox

  • ii. and iv.

  • i. and ii.

  • ii. and iii.

  • i., ii., and iv.

  • ii., iii., and iv.

Correct answer: ii. and iv.

This is a classic combustion equation: a carbon source burns with oxygen in the air to produce carbon dioxide and water vapor. Combustion reactions are always redox reactions, as well: O2 oxidizes the carbon in CH3OH. Initial oxidation states: O = 0, C = -2; final oxidation states: O = -2, C = +4.

76.

You run a reaction with an unknown mechanism and record the remaining concentration of a reactant A at various points in time. You then manipulate the data to determine reaction order. Which of the following findings would support the conclusion that the reaction is second order?

  • The plot of 1/[A] vs. t is linear

  • The plot of 1/[A] vs. t is exponential

  • The plot of ln[A] vs. t is linear

  • The plot of ln[A] vs. t is logistic

  • The plot of [A] vs. t is quadratic

Correct answer: The plot of 1/[A] vs. t is linear

It is useful to remember how to create linear plots from experimental rate data: [A] vs. t for zero order, ln[A] vs. t for first order, and 1/[A] vs. t for second order. These can be derived from the integrated rate laws for each reaction order.

77.

Which of the following simple tests would be a reasonable way to test a liquid's viscosity?

  • Drop a metal ball into a liquid and time how long it takes to reach the bottom

  • Place a slim tube in a liquid and measure how far it climbs or descends along the tube's wall

  • Use a pipette to drop small portions of the liquid onto a hydrophobic surface and observe what shape the liquid takes

  • Use a pipette to drop small portions of the liquid onto an absorbable surface and measure the surface area that becomes wet

  • The term "viscosity" applies only to gases, not liquids

Correct answer: Drop a metal ball into a liquid and time how long it takes to reach the bottom

"Viscosity" is essentially "resistance to flow," and the term applies to both liquids and gases. It can be approximated by dropping an object into the liquid and quantifying its resistance to allowing the object pass through; this is basically equivalent to measuring how resistant the liquid is to flowing across a surface. (Note: this method would not give any absolute number for viscosity, but would allow you to compare the relative viscosities of multiple different liquids).

78.

All of the following are categories of crystalline solids, except:

  • Amorphous solids

  • Ionic solids

  • Covalent solids

  • Molecular solids

  • Metallic solids

Correct answer: Amorphous solids

An amorphous solid like glass lacks a crystalline structure and, therefore, exhibits different behavior.

79.

A carboxyl group has the formula COOH, in which C forms bonds with both O atoms. The electronegativities are as follows: C=2.5, O=3.5, H=2.1 What type of bond occurs between C and O?

  • Polar covalent

  • Non-polar covalent

  • Ionic

  • Could be either non-polar or polar covalent, but can't say without more information

  • Could be either ionic or polar covalent, but can't say without more information

Correct answer: Polar covalent

A polar covalent bond occurs when Δen is between 0.5 and 1.5, while Δen < 0.5 indicates non-polar covalent and Δen > 1.5 indicates ionic. In this case, Δen = 1.0 so the carbon-oxygen bonds are comfortably in the range of polar covalent.

80.

In the Ideal Gas Law PV=nRT, where does the gas constant R come from?

  • The behavior of gas at STP

  • Average deviations from STP

  • Molecular mass of the standard gas

  • Average kinetic energy of gas at STP

  • The volume occupied by a gas at STP

Correct answer: The behavior of gas at STP

R condenses the temperature (273K), volume (22.4L), and pressure (1atm) of a gas at STP into a single number to make gas calculations easier. It essentially provides a reference behavior against which other gases can be compared.

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