MathDB

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2013 USNCO Problem 2: Quantitative Description

A solution of \ce{KNO3} in water is prepared for which the following data have been obtained:

\text{masses of solute and solvent}

\text{molar masses of solute and solvent}

Which of these quantitative descriptions of the solution can be determined?

\text{I. molarity II. molality III. density of solution}

<span class='latex-bold'>(A) </span>\text{I. only}\qquad<span class='latex-bold'>(B) </span>\text{II. only}\qquad<span class='latex-bold'>(C) </span>\text{I. and II. only}\qquad<span class='latex-bold'>(D) </span>\text{I., II. and III.}\qquad

3

1

2013 USNCO Problem 3: Mass of compound

What mass of the compound \ce{CrO3}

\text{(M = 100.0)}

contains

4.5\times10^{23}

oxygen atoms?

<span class='latex-bold'>(A) </span>\text{2.25 g}\qquad<span class='latex-bold'>(B) </span>\text{12.0 g}\qquad<span class='latex-bold'>(C) </span>\text{25.0 g}\qquad<span class='latex-bold'>(D) </span>\text{75.0 g}\qquad

4

1

2013 USNCO Problem 4: Tin Empirical Formula

An

18.5

g sample of tin

\text{(M = 118.7)}

combines with

10.0

g of sulfur

\text{(M = 32.07)}

to form a compound. What is the empirical formula of this compound?
(A) \ce{SnS}\qquad(B) \ce{SnS2}\qquad(C) \ce{Sn2S}\qquad(D) \ce{Sn2S3}\qquad

5

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2013 USNCO Problem 5: Hydroxide Concentration

A mixture is prepared by adding

50.0

mL of

0.200

M \ce{NaOH} to

75.0

mL of

0.100

M \ce{NaOH}. What is the $$$[OH^-]$ in the mixture?
$ (A) \text{0.0600 M}\qquad(B) \text{0.0800 M}\qquad(C) \text{0.140 M}\qquad(D) \text{0.233 M}\qquad$

6

1

2013 USNCO Problem 6: Mass

What mass of \ce{NaHCO3}

(\text{M=84})

is required to completely neutralize

25.0

mL of

0.125

M \ce{H2SO4}?

<span class='latex-bold'>(A) </span>\text{0.131 g}\qquad<span class='latex-bold'>(B) </span>\text{0.262 g}\qquad<span class='latex-bold'>(C) </span>\text{0.525 g}\qquad<span class='latex-bold'>(D) </span>\text{1.05 g}\qquad

7

1

2013 USNCO Problem 7: Seperation of solid

A solid can be separated from a liquid by all the following means EXCEPT

<span class='latex-bold'>(A) </span>\text{decantation} \qquad<span class='latex-bold'>(B) </span>\text{distillation}\qquad

<span class='latex-bold'>(C) </span>\text{filtration}\qquad<span class='latex-bold'>(D) </span>\text{hydration}\qquad

37

1

2013 USNCO Problem 37: Reduction Potentials

Three metals,

A, B

and

C

, with solutions of their respective cations are tested in a voltaic cell with the following results:

A

and

B

:

A

is the cathode

B

and

C

:

C

is the cathode

A

and

C

:

A

is the anode
What is the order of the reduction potentials from highest to lowest for the cations of these metals?

<span class='latex-bold'>(A)</span>\ A>B>C \qquad<span class='latex-bold'>(B)</span>\ B>C>A\qquad

{<span class='latex-bold'>(C)</span>\ C>A>B\qquad<span class='latex-bold'>(D</span>}\ B>A>C\qquad

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1

2013 USNCO Problem 38: Oxidation State

In which pair of substances do the nitrogen atoms have the same oxidation state?
(A)\ \ce{HNO3} \text{ and } \ce{ N2O5} \qquad(B)\ \ce{NO} \text{ and } \ce{HNO2} \qquad
{(C)\ \ce{N2} \text{ and } \ce{N2O} \qquad(D)}\ \ce{HNO2} \text{ and } \ce{HNO3} \qquad

42

1

2013 USNCO Problem 42: Electrochemistry

Use the standard reduction potentials to determine what is observed at the cathode during the electrolysis of a

1.0 \text{M}

solution of \ce{KBr} that contains phenolphthalein. What observation(s) is(are) made?
\ce{O2 (g)} + \ce{4H^+ (aq)} + 4e^- \rightarrow \ce{2H2O (l) }; \text{ E}^\circ = \text{1.23 V} \ce{Br2 (l)} + 2e^- \rightarrow \ce{2Br^- (aq)} ; \text{ E}^\circ = \text{1.07 V} \ce{2H2O (l)} + 2e^- \rightarrow \ce{H2 (g)} + \ce{2OH^-} ; \text{ E}^\circ = \text{-0.80 V} \ce{K^+ (aq)} + e^- \rightarrow \ce{K (s)} ; \text{ E}^\circ = \text{-2.92 V}

<span class='latex-bold'>(A) </span>\text{Solid metal forms}\qquad

<span class='latex-bold'>(B) </span>\text{Bubbles form and a pink color appears}\qquad

(C) \text{Dark red } \ce{ Br2} \text{ forms}\qquad

<span class='latex-bold'>(D) </span>\text{Bubbles form and the solution remains colorless}\qquad

43

1

2013 USNCO Problem 43: Discovery of the nuclear atom

To whom is the discovery of the nuclear atom attributed?

<span class='latex-bold'>(A) </span>\text{Neils Bohr}\qquad<span class='latex-bold'>(B) </span>\text{Louis deBroglie}\qquad

<span class='latex-bold'>(C) </span>\text{Robert Millikan}\qquad<span class='latex-bold'>(D) </span>\text{Ernest Rutherford}\qquad

44

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2013 USNCO Problem 44: Atomic Orbitals

Each of the following atomic orbitals is possible except

<span class='latex-bold'>(A) </span> 1s \qquad<span class='latex-bold'>(B) </span> 2p \qquad<span class='latex-bold'>(C) </span> 3f \qquad<span class='latex-bold'>(D) </span> 4d \qquad

46

1

2013 USNCO Problem 46: Flame Test

What is the characteristic color of the flame test for potassium?

{ <span class='latex-bold'>(A)</span>\ \text{yellow}\qquad<span class='latex-bold'>(B)</span>\ \text{red}\qquad<span class='latex-bold'>(C)</span>\ \text{green}\qquad<span class='latex-bold'>(D)</span>}\ \text{violet}\qquad

47

1

2013 USNCO Problem 47: Electronegativity

Which atom has the highest electronegativity?

{ <span class='latex-bold'>(A)</span>\ \text{Na}\qquad<span class='latex-bold'>(B)</span>\ \text{P}\qquad<span class='latex-bold'>(C)</span>\ \text{Cl}\qquad<span class='latex-bold'>(D)</span>}\ \text{Br}\qquad

48

1

2013 USNCO Problem 48: Metalloids

In which set are both elements metalloids?

{ <span class='latex-bold'>(A)</span>\ \text{Cr and Mo}\qquad<span class='latex-bold'>(B)</span>\ \text{Ge and As}\qquad<span class='latex-bold'>(C)</span>\ \text{Sn and Pb}\qquad<span class='latex-bold'>(D)</span>}\ \text{Se and Br}\qquad

50

1

2013 USNCO Problem 50: Strongest Bond

Which bond is strongest?

{ <span class='latex-bold'>(A)</span>\ \text{C=C}\qquad<span class='latex-bold'>(B)</span>\ \text{C=N}\qquad<span class='latex-bold'>(C)</span>\ \text{C=O}\qquad<span class='latex-bold'>(D)</span>}\ \text{C=S}\qquad

49

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2013 USNCO Problem 49: Silicon Dioxide Bond

The silicon-oxygen bonds in \ce{SiO2} are best described as

{ <span class='latex-bold'>(A)</span>\ \text{coordinate covalent}\qquad<span class='latex-bold'>(B)</span>\ \text{ionic}\qquad<span class='latex-bold'>(C)</span>\ \text{nonpolar covalent}\qquad<span class='latex-bold'>(D)</span>}\ \text{polar covalent}\qquad

52

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2013 USNCO Problem 52: Smallest Angle

If

\text{A}

represents the central atom, in which molecule is the

\text{F-A-F}

angle the smallest?
(A) \ce{BF3} \qquad(B) \ce{CF4} \qquad(C) \ce{NF3} \qquad(D) \ce{OF2} \qquad

54

1

2013 USNCO Problem 54: Sigma and Pi bonds

How many sigma

(\sigma)

and pi

(\pi)

bonds are in a molecule of ethyne (acetylene), \ce{HCCH}?

<span class='latex-bold'>(A) </span> 1 \sigma \text{ and } 1 \pi \qquad<span class='latex-bold'>(B) </span>2 \sigma \text{ and } 1 \pi \qquad<span class='latex-bold'>(C) </span>2 \sigma \text{ and } 3\pi \qquad<span class='latex-bold'>(D) </span>3 \sigma \text{ and } 2 \pi\qquad

53

1

2013 USNCO Problem 53: VSPER Theory

On the basis of VSEPR theory, what geometry is predicted for the central sulfur atom in \ce{SOCl2}?

<span class='latex-bold'>(A) </span>\text{bent}\qquad<span class='latex-bold'>(B) </span>\text{T-shaped}\qquad<span class='latex-bold'>(C) </span>\text{trigonal planar} \qquad<span class='latex-bold'>(D) </span>\text{trigonal pyramidal} \qquad

55

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2013 USNCO Problem 55: Number of isomers

What is the number of structural isomers with the molecular formula \ce{C6H14}?

<span class='latex-bold'>(A) </span>\text{Three} \qquad<span class='latex-bold'>(B) </span>\text{Four} \qquad<span class='latex-bold'>(C) </span>\text{Five} \qquad<span class='latex-bold'>(D) </span>\text{Six}\qquad

57

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2013 USNCO Problem 57: Oxidation

Methanol can be gently oxidized with hot copper metal. What is(are) the product(s) of this oxidation?

<span class='latex-bold'>(A) </span>\text{Acetic acid}\qquad<span class='latex-bold'>(B) </span>\text{Carbon dioxide + Water}\qquad<span class='latex-bold'>(C) </span>\text{Ethanol} \qquad<span class='latex-bold'>(D) </span>\text{Methanal} \qquad

56

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2013 USNCO Problem 56: Condensation Polymers

All of the following are condensation polymers except:

<span class='latex-bold'>(A) </span>\text{Nylon} \qquad<span class='latex-bold'>(B) </span>\text{Polyethylene}\qquad<span class='latex-bold'>(C) </span>\text{Protein} \qquad<span class='latex-bold'>(D) </span>\text{Starch}\qquad

58

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2013 USNCO Problem 58: Benzene

Which statement does not describe benzene, \ce{C6H6}?

<span class='latex-bold'>(A)</span>\ \text{It is an aromatic hydrocarbon.} \qquad

<span class='latex-bold'>(B)</span>\ \text{It exists in two isomeric forms.} \qquad

<span class='latex-bold'>(C)</span>\ \text{It undergoes substitution reactions.} \qquad

<span class='latex-bold'>(D)</span>\ \text{It can react to form three different products with the formula C}_6\text{H}_4\text{Cl}_2\qquad

60

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2013 USNCO Problem 60: Most soluable vitamin

Which vitamin is the most soluble in water?

{ <span class='latex-bold'>(A)</span>\ \text{A} \qquad<span class='latex-bold'>(B)</span>\ \text{K} \qquad<span class='latex-bold'>(C)</span>\ \text{C} \qquad<span class='latex-bold'>(D)</span>}\ \text{D} \qquad

59

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2013 USNCO Problem 59: Peptide Functional Group

All of the following atoms comprise part of a peptide functional group except:

<span class='latex-bold'>(A)</span>\ \text{Hydrogen} \qquad<span class='latex-bold'>(B)</span>\ \text{Nitrogen}\qquad

{<span class='latex-bold'>(C)</span>\ \text{Oxygen} \qquad<span class='latex-bold'>(D)</span>}\ \text{Phosphorous} \qquad

2013 National Chemistry Olympiad

Subcontests

2013 USNCO Problem 2: Quantitative Description

2013 USNCO Problem 3: Mass of compound

2013 USNCO Problem 4: Tin Empirical Formula

2013 USNCO Problem 5: Hydroxide Concentration

2013 USNCO Problem 6: Mass

2013 USNCO Problem 7: Seperation of solid

2013 USNCO Problem 37: Reduction Potentials

2013 USNCO Problem 38: Oxidation State

2013 USNCO Problem 42: Electrochemistry

2013 USNCO Problem 43: Discovery of the nuclear atom

2013 USNCO Problem 44: Atomic Orbitals

2013 USNCO Problem 46: Flame Test

2013 USNCO Problem 47: Electronegativity

2013 USNCO Problem 48: Metalloids

2013 USNCO Problem 50: Strongest Bond

2013 USNCO Problem 49: Silicon Dioxide Bond

2013 USNCO Problem 52: Smallest Angle

2013 USNCO Problem 54: Sigma and Pi bonds

2013 USNCO Problem 53: VSPER Theory

2013 USNCO Problem 55: Number of isomers

2013 USNCO Problem 57: Oxidation

2013 USNCO Problem 56: Condensation Polymers

2013 USNCO Problem 58: Benzene

2013 USNCO Problem 60: Most soluable vitamin

2013 USNCO Problem 59: Peptide Functional Group