Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 17

A portion of the phase diagram of uranium hexafluoride (UF6) is shown below.

Which statements are correct?

I.  UF6 sublimes at atmospheric pressure.
II. At 80 ºC and 1.5 atm, only UF6(g) is present at equilibrium.
(A) I only
(B) II only
(C) Both I and II
(D) Neither I nor II
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 5

Which of the following combinations will produce a 0.4 M NaCl solution?

(A) Mixing 500 mL of 0.4 M NaOH with 500 mL of 0.4 M HCl
(B) Mixing 300 mL of 1.2 M NaOH with 600 mL of 0.6 M HCl
(C) Mixing 500 mL of 0.4 M NaCl solution with 500 mL water
(D) Diluting 400 mL of 0.6 M NaCl with water to a final volume of 1.0 L
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 22

For a constant-pressure process, what is the difference between the internal energy change (∆U) and the enthalpy change (∆H)?

(A) Heat
(B) Work
(C) Entropy
(D) Gibbs free energy
Chemistry

Which type of change is different from the other four?

(A) Baking a potato
(B) Rusting of an iron nail
(C) Burning a piece of paper
(D) Melting an ice cube
(E) Ignition of propane
Chemistry

At which temperature does a water sample have the highest average kinetic energy?

(A) 0 degrees Celsius
(B) 100 degrees Celsius
(C) 0 K
(D) 100 K
(E) 273 K
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 16

A two-dimensional slice through the lattice of a crystalline solid containing two different elements X and Y is shown schematically and to scale below. What type of solid is it?

(A) A metallic alloy such as FeCr
(B) A molecular solid such as IBr
(C) An ionic compound such as LiCl
(D) A network covalent solid such as SiC
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 7

A solution of which compound gives a violet flame test?

(A) LiBr
(B) NaCl
(C) KNO3
(D) B(OH)3
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 10

Which methods would be suitable for determining the concentration of an aqueous solution of KMnO4?

I. Visible spectrophotometry (colorimetry)
II. Redox titration
(A) I only
(B) II only
(C) Both I and II
(D) Neither I nor II
Chemistry

Which of the following is not a conclusion Rutherford made from his experiment with alpha particles being shot at a thin sheet of gold foil?

(A) An atom has a very small, compact nucleus.
(B) An atom is mainly empty space.
(C) An atom’s mass is concentrated in the nucleus.
(D) An atom has a very dense nucleus.
(E) An atom has a negatively charged nucleus.
Chemistry

Which gas is expected to have the highestrate of effusion?

(A) O2
(B) F2
(C) H2O
(D) He
(E) CH2