MathDB

2010 National Chemistry Olympiad

Part of National Chemistry Olympiad

Subcontests

(20)
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2010 USNCO Local #23: Spontaneity

What are the signs of △H\triangle{H} and △S\triangle{S} for a reaction that is spontaneous only at low temperatures?
<spanclass=′latex−bold′>(A)</span> △H is positive,△S is positive<spanclass=′latex−bold′>(B)</span> △H is positive,△S is negative <span class='latex-bold'>(A)</span>\ \triangle{H} \text{ is positive}, \triangle{S} \text{ is positive} \qquad<span class='latex-bold'>(B)</span>\ \triangle{H}\text{ is positive}, \triangle{S} \text{ is negative} \qquad
<spanclass=′latex−bold′>(C)</span> △H is negative,△S is negative<spanclass=′latex−bold′>(D)</span> △H is negative,△S is positive<span class='latex-bold'>(C)</span>\ \triangle{H} \text{ is negative}, \triangle{S} \text{ is negative} \qquad<span class='latex-bold'>(D)</span>\ \triangle{H} \text{ is negative}, \triangle{S} \text{ is positive} \qquad
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2010 USNCO Local #18: Critical Temperature

The critical temperature of water is the
<spanclass=′latex−bold′>(A)</span>temperature at which solid, liquid and gaseous water coexist <span class='latex-bold'>(A)</span>\hspace{.05in}\text{temperature at which solid, liquid and gaseous water coexist} \qquad <spanclass=′latex−bold′>(B)</span>temperature at which water vapor condenses<span class='latex-bold'>(B)</span>\hspace{.05in}\text{temperature at which water vapor condenses}\qquad <spanclass=′latex−bold′>(C)</span>maximum temperature at which liquid water can exist<span class='latex-bold'>(C)</span>\hspace{.05in}\text{maximum temperature at which liquid water can exist}\qquad <spanclass=′latex−bold′>(D)</span>minimum temperature at which water vapor can exist<span class='latex-bold'>(D)</span>\hspace{.05in}\text{minimum temperature at which water vapor can exist}\qquad
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2010 USNCO Local #12: Molarity of Acetic Acid

Commercial vinegar is a 5.00%5.00\% by mass aqueous solution of acetic acid, \ce{CH3CO2H} (M=60.0)(M=60.0). What is the molarity of acetic acid in vinegar? [density of vinegar = 1.00g/mL)
<spanclass=′latex−bold′>(A)</span>0.833M<spanclass=′latex−bold′>(B)</span>1.00M<spanclass=′latex−bold′>(C)</span>1.20M<spanclass=′latex−bold′>(D)</span>3.00M <span class='latex-bold'>(A)</span>\hspace{.05in}0.833 M\qquad<span class='latex-bold'>(B)</span>\hspace{.05in}1.00 M\qquad<span class='latex-bold'>(C)</span>\hspace{.05in}1.20 M\qquad<span class='latex-bold'>(D)</span>\hspace{.05in}3.00 M\qquad
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2010 USNCO Local #14: Family of Elements

Which family of elements has solid, liquid, and gaseous members at 25∘C25^{\circ} \text{C} and 1atm1 \text{atm} pressure?
<spanclass=′latex−bold′>(A)</span>alkali metals (Li-Cs)<spanclass=′latex−bold′>(B)</span>pnictogens (N-Bi) <span class='latex-bold'>(A)</span>\hspace{.05in}\text{alkali metals (Li-Cs)} \qquad<span class='latex-bold'>(B)</span>\hspace{.05in}\text{pnictogens (N-Bi)} \qquad <spanclass=′latex−bold′>(C)</span>chalcogens (O-Te)<spanclass=′latex−bold′>(D)</span>halogens (F-I)<span class='latex-bold'>(C)</span>\hspace{.05in}\text{chalcogens (O-Te)} \qquad<span class='latex-bold'>(D)</span>\hspace{.05in}\text{halogens (F-I)}\qquad
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2010 USNCO Local #13: Gas Law

A 2.00L2.00 \text{L} balloon at 20.0∘C20.0^{\circ} \text{C} and 745mmHg745 \text{mmHg} floats to an altitude where the temperature is 10.0∘C10.0^{\circ} \text{C} and the air pressure is 700mmHg700 \text{mmHg}. What is the new volume of the balloon?
<spanclass=′latex−bold′>(A)</span>0.94L<spanclass=′latex−bold′>(B)</span>1.06L<spanclass=′latex−bold′>(C)</span>2.06L<spanclass=′latex−bold′>(D)</span>2.20L <span class='latex-bold'>(A)</span>\hspace{.05in}0.94 \text{L}\qquad<span class='latex-bold'>(B)</span>\hspace{.05in}1.06 \text{L}\qquad<span class='latex-bold'>(C)</span>\hspace{.05in}2.06 \text{L}\qquad<span class='latex-bold'>(D)</span>\hspace{.05in}2.20 \text{L}\qquad
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2010 USNCO Local #11: Converting Glucose to Ethanol

Enzymes convert glucose (M=180.2)(M=180.2) to ethanol (M=46.1)(M=46.1) according to the equation
C6H12O6→2C2H2OH+2CO2 \text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_2\text{OH} + 2\text{CO}_2
What is the maximum mass of ethanol that can be made from 15.515.5 kg of glucose?
<spanclass=′latex−bold′>(A)</span>0.256kg<spanclass=′latex−bold′>(B)</span>0.512kg<spanclass=′latex−bold′>(C)</span>3.96kg<spanclass=′latex−bold′>(D)</span>7.93kg <span class='latex-bold'>(A)</span>\hspace{.05in}0.256 \text{kg}\qquad<span class='latex-bold'>(B)</span>\hspace{.05in}0.512 \text{kg} \qquad<span class='latex-bold'>(C)</span>\hspace{.05in}3.96 \text{kg}\qquad<span class='latex-bold'>(D)</span>\hspace{.05in}7.93 \text{kg}\qquad
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2010 USNCO Local #10: Solubility Rule

Magnesium chloride dissolves in water to form:
<spanclass=′latex−bold′>(A)</span>hydrated MgCl2molecules <span class='latex-bold'>(A)</span>\hspace{.05in}\text{hydrated MgCl}_2 \text{molecules}\qquad <spanclass=′latex−bold′>(B)</span>hydrated Mg2+ions and hydrated Cl−ions<span class='latex-bold'>(B)</span>\hspace{.05in}\text{hydrated Mg}^{2+} \text{ions and hydrated Cl}^- \text{ions} \qquad <spanclass=′latex−bold′>(C)</span>hydrated Mg2+ions and hydrated Cl22−ions<span class='latex-bold'>(C)</span>\hspace{.05in}\text{hydrated Mg}^{2+} \text{ions and hydrated Cl}_2 ^{2-} \text{ions}\qquad <spanclass=′latex−bold′>(D)</span>hydrated Mg atoms and hydrated Cl2molecules<span class='latex-bold'>(D)</span>\hspace{.05in}\text{hydrated Mg atoms and hydrated Cl}_2 \text{molecules}\qquad
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2010 USNCO Local #9: Number of Neutrons

How many neutrons are in 0.0250.025 mol of the isotope 2454Cr{ }_{24}^{54}\text{Cr}?
<spanclass=′latex−bold′>(A)</span>1.5×1022<spanclass=′latex−bold′>(B)</span>3.6×1023<spanclass=′latex−bold′>(C)</span>4.5×1023<spanclass=′latex−bold′>(D)</span>8.1×1023 <span class='latex-bold'>(A)</span>\hspace{.05in}1.5\times10^{22} \qquad<span class='latex-bold'>(B)</span>\hspace{.05in}3.6\times10^{23} \qquad<span class='latex-bold'>(C)</span>\hspace{.05in}4.5\times10^{23} \qquad<span class='latex-bold'>(D)</span>\hspace{.05in}8.1\times10^{23} \qquad
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2010 USNCO Local #8: Highest Percentage by Mass

Which compound contains the highest percentage of nitrogen by mass?
<spanclass=′latex−bold′>(A)</span>NH2OH(M=33.0)<spanclass=′latex−bold′>(B)</span>NH4NO2(M=64.1) <span class='latex-bold'>(A)</span> \text{NH}_2\text{OH} (M=33.0) \qquad<span class='latex-bold'>(B)</span>\text{NH}_4\text{NO}_2 (M=64.1)\qquad <spanclass=′latex−bold′>(C)</span>N2O3(M=76.0)<spanclass=′latex−bold′>(D)</span>NH4NH2CO2(M=78.1)<span class='latex-bold'>(C)</span>\text{N}_2\text{O}_3 (M=76.0)\qquad<span class='latex-bold'>(D)</span>\text{NH}_4\text{NH}_2\text{CO}_2 (M=78.1)\qquad
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2010 USNCO Local #7: Balancing an equation

What is the coefficient for O2\text{O}_2 when the following reaction _As2S3+_O2→_As2O3+_SO2\_\text{As}_2\text{S}_3+\_\text{O}_2 \rightarrow \_\text{As}_2\text{O}_3+\_\text{SO}_2 is correctly balanced with the smallest integer coefficients?
<spanclass=′latex−bold′>(A)</span>5<spanclass=′latex−bold′>(B)</span>6<spanclass=′latex−bold′>(C)</span>8<spanclass=′latex−bold′>(D)</span>9 <span class='latex-bold'>(A)</span> 5 \qquad<span class='latex-bold'>(B)</span> 6 \qquad<span class='latex-bold'>(C)</span> 8 \qquad<span class='latex-bold'>(D)</span> 9 \qquad
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2010 USNCO Local #5: Explanation for Error

A student performed an experiment to determine the ratio of H2O\text{H}_2\text{O} to CuSO4\text{CuSO}_4 in a sample of hydrated copper(II) sulfate by heating it to drive off the water and weighing the solid before and after heating. The formula obtained experimentally was CuSO4∙5.5H2O\text{CuSO}_4 \bullet 5.5\text{H}_2\text{O} but the accepted formula is CuSO4∙5H2O\text{CuSO}_4 \bullet 5 \text{H}_2\text{O}. Which error best accounts for the difference in results?
<spanclass=′latex−bold′>(A)</span> During heating some of the hydrated copper(II) sulfate was lost <span class='latex-bold'>(A)</span>\ \text{During heating some of the hydrated copper(II) sulfate was lost} \qquad <spanclass=′latex−bold′>(B)</span> The hydrated sample was not heated long enough to drive off all the water<span class='latex-bold'>(B)</span>\ \text{The hydrated sample was not heated long enough to drive off all the water}\qquad <spanclass=′latex−bold′>(C)</span> The student weighed out too much sample initially.<span class='latex-bold'>(C)</span>\ \text{The student weighed out too much sample initially.} \qquad <spanclass=′latex−bold′>(D)</span> The student used a balance that gave weights that were consistently too high by 0.10 g <span class='latex-bold'>(D)</span>\ \text{The student used a balance that gave weights that were consistently too high by 0.10 g }\qquad
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2010 USNCO Local #6: Reagent for Precipitation

An aqueous solution is known to contain Ag+,Mg2+,\text{Ag}^+, \text{Mg}^{2+}, and Sr2+\text{Sr}^{2+} ions. Which reagent should be used to selectively precipitate the Ag+\text{Ag}^+?
<spanclass=′latex−bold′>(A)</span> 0.20M NaCl<spanclass=′latex−bold′>(B)</span> 0.20M NaOH<spanclass=′latex−bold′>(C)</span> 0.20M Na2SO4<spanclass=′latex−bold′>(D)</span> 0.20M Na3PO4{ <span class='latex-bold'>(A)</span>\ 0.20 \text{M NaCl} \qquad<span class='latex-bold'>(B)</span>\ 0.20 \text{M NaOH} \qquad<span class='latex-bold'>(C)</span>\ 0.20 \text{M Na}_2\text{SO}_4 \qquad<span class='latex-bold'>(D)</span>\ 0.20 \text{M Na}_3\text{PO}_4 }
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2010 USNCO Local #4: Solid Camphore in Water &amp; Veg. Oil

Solid camphor is insoluble in water but is soluble in vegetable oil. The best explanation for this behavior is that camphor is a(n)
<spanclass=′latex−bold′>(A)</span> Ionic solid<spanclass=′latex−bold′>(B)</span> Metallic solid<spanclass=′latex−bold′>(C)</span> Molecular solid<spanclass=′latex−bold′>(D)</span> Network solid{ <span class='latex-bold'>(A)</span>\ \text{Ionic solid} \qquad<span class='latex-bold'>(B)</span>\ \text{Metallic solid} \qquad<span class='latex-bold'>(C)</span>\ \text{Molecular solid} \qquad<span class='latex-bold'>(D)</span>\ \text{Network solid} }
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2010 USNCO Local #3: Phenolphythalein in a solution

When phenolphythalein is added to an aqueous solution containing one of the following solutes the solution turns pink. Which solute is present?
<spanclass=′latex−bold′>(A)</span> NaCl<spanclass=′latex−bold′>(B)</span> KC2H3O2<spanclass=′latex−bold′>(C)</span> LiBr<spanclass=′latex−bold′>(D)</span> NH4NO3{ <span class='latex-bold'>(A)</span>\ \text{NaCl} \qquad<span class='latex-bold'>(B)</span>\ \text{KC}_2\text{H}_3\text{O}_2 \qquad<span class='latex-bold'>(C)</span>\ \text{LiBr} \qquad<span class='latex-bold'>(D)</span>\ \text{NH}_4\text{NO}_3 }
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2010 USNCO Local #2: Flame Test

A flame test was performed to confirm the identity of a metal ion in solution. The result was a green flame. Which of the following metal ions is indicated?
<spanclass=′latex−bold′>(A)</span> copper<spanclass=′latex−bold′>(B)</span> sodium<spanclass=′latex−bold′>(C)</span> strontium<spanclass=′latex−bold′>(D)</span> zinc{ <span class='latex-bold'>(A)</span>\ \text{copper} \qquad<span class='latex-bold'>(B)</span>\ \text{sodium} \qquad<span class='latex-bold'>(C)</span>\ \text{strontium} \qquad<span class='latex-bold'>(D)</span>\ \text{zinc} }
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2010 USNCO Local #1: Methanol Experiment

A student is asked to measure 30.0g30.0 {\text{g}} of methanol (d=0.7914g/mL at 25∘C)(d=0.7914 \text{g/mL at 25}^{\circ}\text{C}) but has only a graduated cylinder with which to measure it. What volume of methanol should the student use to obtain the required 30.0g{30.0 \text{g}}?
<spanclass=′latex−bold′>(A)</span> 23.7mL<spanclass=′latex−bold′>(B)</span> 30.0mL<spanclass=′latex−bold′>(C)</span> 32.4mL<spanclass=′latex−bold′>(D)</span> 37.9mL{ <span class='latex-bold'>(A)</span>\ 23.7 \text{mL} \qquad<span class='latex-bold'>(B)</span>\ 30.0 \text{mL} \qquad<span class='latex-bold'>(C)</span>\ 32.4 \text{mL} \qquad<span class='latex-bold'>(D)</span>\ 37.9 \text{mL} }