1993 - U.S National Chemistry Olympiad 1993 Local Test Go...

U.S. National Chemistry Olympiad: 1993 Local Test
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1. Which diagram is the best representation for a mixture of hydrogen and helium at 25 °C and 1
atm?
2. Which combination of 1 M solutions will produce a visible reaction when mixed?
Solution Mixtures:
I. HCl and Pb(NO
3
)
2
II. HCl and NaOH
III. HCl and Na
2
CO
3
(A) I and II only
(B) I and III only
(C) II and III only
(D) I, II, III
3. Which physical property would be most useful for determining whether two samples of metal
are the same metal?

4. Which technique could be used to separate a homogeneous mixture?
Techniques:
I. chromatography
II. distillation
III. filtration
5. How many of these elements are liquids at 25 °C and 1 atm?
Elements:
mercury
phosphorus
radon
6. What is the mole fraction of methanol, CH
3
OH, in a solution of methanol and water that
contains 50 g of each?
Substance Molar Mass
CH
3
OH 32 g mol¯
1
H
2
O 18 g mol¯
1
(A) 0.18
(B) 0.36
(C) 0.50
(D) 0.64
7. Ammonia can be reacted with oxygen to form nitrogen(II) oxide and water according to the
unbalanced equation
_NH
3
+ _O
2
---> _ NO + _H
2
O
When this equation is balanced with the simplest set of whole number coefficients, the
coefficients are

8. A lab manual directs a student to measure a piece of ribbon 5.00 cm long and calculate its
mass from the mass of 100.00 cm of the ribbon (0.985 g). Why is this approach superior to
simply cutting a 5.00 cm piece of ribbon and determining its mass on an electronic milligram
balance?
9. What should be done to prepare 500.0 mL of a 0.200 M solution of NaCl?
The Molar Mass of NaCl is 58.45 g mol¯
1
10. Equal masses of O
2
and N
2
are reacted according to this equation:
O
2
+ N
2
---> 2 NO
Which statement is true?
(A) O
2
is the limiting reagent and N
2
is present in excess
(B) N
2
is the limiting reagent and O
2
is present in excess
(C) all of the O
2
and N
2
react and neither is in excess
(D) Nothing can be said about the limiting reagent