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 1

Which hydrocarbon is 84.1% carbon by mass?

(A) CH4
(B) C2H6
(C) C4H10
(D) C8H18
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 12

Which is the best way to dispense liquids using a volumetric pipet?

(A) The pipet is immersed in the liquid to be dispensed, then lifted with a gloved finger on the top and the liquid allowed to drain to the mark. The remaining contents are then allowed to drain into the desired container.
(B) The pipet is immersed in the liquid to be dispensed, then lifted with a gloved finger on the top and the liquid allowed to drain to the mark. The remaining contents are then allowed to drain into the desired container, with a pipet bulb used to gently blow out any residual droplets.
(C) The tip of the pipet is submerged below the surface of the liquid and suction is applied using a pipet bulb until the liquid rises above the level of the mark. A gloved finger is then applied to the top of the pipet and the liquid allowed to drain to the mark. The remaining contents are then allowed to drain into the desired container.
(D)  The tip of the pipet is submerged below the surface of the liquid and suction is applied by mouth until the liquid rises to the level of the mark. The contents are then allowed to drain into the desired container.
Chemistry

An atom has eight electrons in a 3d subshell. How many orbitals in this subshell have an unpaired electron?

(A) 1
(B) 2
(C) 3
(D) 4
(E) 5
Chemistry

Which units could be used to express the amount of energy absorbed or released during a chemical reaction?

(A) Degree and gram
(B) Torr and mmHg
(C) Gram and liter
(D) Calorie and joule
(E) Meter and cm3
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

Which gas under a high temperature and a low pressure behaves most like an ideal gas?

(A) He
(B) O2
(C) NH3
(D) CO2
(E) Ne
Chemistry

2019 U.S. National Chemistry Olympiad Local Section Exam Question 3

A vessel contains 66 g CO2 and 16 g O2 at a pressure of 10.0 atm. What is the partial pressure of CO2?

(A) 5.0 atm
(B) 6.0 atm
(C) 7.5 atm
(D) 8.0 atm
Chemistry

Which substance cannot be decomposed chemically?

(A) Ammonia
(B) Tellurium
(C) Methane
(D) Water
(E) Lunch
Chemistry

Which substance can be decomposed chemically?

(A) Ammonia
(B) Iron
(C) Neon
(D) Hydrogen
(E) Fluorine