HighFour Chemistry
Category C: Grades 9 – 10
Round 9
Tuesday, May 10, 2016
The use of calculator is required.
Question #1
How many kilograms of iron could be obtained from 5400 g of FeCO3?
Question #2
In an experiment, what do you call a tentative explanation for a set of
observations based on the data gathered?
Question #3
At one time there was a chemical atomic mass scale based on the
assignment of the value 16.0000 to naturally occurring oxygen. What would
have been the atomic mass, on such a table, of silver, if current information
had been available? The atomic masses of oxygen and silver on the present
table are 15.9994 and 107.8682.
Question #4
A 12.5843 g sample of ZrBr4 was dissolved and, after several chemical steps,
all of the combined bromine was precipitated as AgBr. The silver content of
the AgBr was found to be 13.2160 g. Assume the atomic masses of silver
and bromine to be 107.868 and 79.904, respectively. What value was
obtained for the atomic mass of Zr from this experiment?
Question #5
What do you call the instrument that separates particles of different
isotopic composition and measures their individual relative masses?
HighFour Chemistry
Category C: Grades 9 – 10
Round 9
Tuesday, May 10, 2016
The use of calculator is required.
Question #6
A 15.00 g sample of a hydrated salt, Na2SO4· XH2O, was found to contain
7.05 g of water. Determine X in the given formula.
Question #7
A compound gave on analysis the following percentage composition:
K = 26.57%, Cr = 35.36%, O = 38.07%. Find x, y, and z to derive the empirical
formula of the compound KXCryOz.
(Use molecular weight of K= 39.10 g/mol; Cr =52 g/mol; O=16g/mol)
Question #8
How much 56.0% sulfuric acid solution is needed to provide 150 g of H2SO4?
Question #9
Calculate the mass of pure HNO3 per cm3 of the concentrated acid which
assays 69.8% by weight HNO3 and has a density of 1.45 g/cm3.
Question #10
The blue iridescence of butterfly wings is due to
striations that are 0.15 µm apart, as measured
by the electron microscope. What is this
distance in centimeters? (Use ^ for “raise to”
ex. 105 or 10^5)
HighFour Chemistry
Category C: Grades 9 – 10
Round 9
Tuesday, May 10, 2016
The use of calculator is required.
Question #11
Determine the molar mass of potassium
hexachloroiridate (IV).
(Use molecular weight of K= 39.10 g/mol;
Cl =35.45 g/mol; Ir=192.22g/mol)
Question #12
How many molecules are contained in 92.91 g of P4?
(Use ^ for “raise to” ex. 105 or 10^5)
(Use molecular weight of P= 30.947 g/mol)
Question #13
The bromine content of average ocean water is 65 parts by weight per
million. Assuming 100 percent recovery, how many cubic meters of ocean
water must be processed to produce 0.61 kg of bromine? Assume that the
density of seawater is 1.0 x 103 kg/m3.
Question #14
What is the mass (kg) of one molecule of C1200H2000O1000?
(Use ^ for “raise to” ex. 105 or 10^5)
(Use molecular weight of C= 12 g/mol; H =1 g/mol; O=16g/mol)
Question #15
How many moles of N are contained in 132.4 g of Cd(NO3)2 ·4H2O?
(Use molecular weight of Cd= 112.411 g/mol; H =1 g/mol; O=16g/mol;
N = 14g/mol)
HighFour Chemistry
Category C: Grades 9 – 10
Round 9
Tuesday, May 10, 2016
The use of calculator is required.
Question #16
How many molecules of water of hydration are in 132.4 g of
Cd(NO3)2 ·5H2O?
(Use ^ for “raise to” ex. 105 or 10^5)
(Use molecular weight of Cd= 112.411 g/mol; H =1 g/mol; O=16g/mol;
N = 14g/mol)
Question #17
A 5.82 g silver coin is dissolved in nitric acid. When sodium
chloride is added to the solution, all the silver is
precipitated as AgCl. The AgCl precipitate weighs 7.20 g.
Determine the percentage of silver in the coin.
(Use molecular weight of Ag= 107.9 g/mol; Cl =35.45 g/mol)
Question #18
A 1.2048 g impure sample of Na2CO3 is dissolved and allowed to react with
a solution of CaCl2. The resulting CaCO3, after precipitation, filtration, and
drying, was found to weigh 1.0262 g. Assuming that the impurities do not
contribute to the weight of the precipitate, calculate the percentage purity
of the Na2CO3
(Use molecular weight of Na= 23 g/mol; Ca =40 g/mol; O=16 g/mol;
C=12g/mol)
Question #19
How high (m) a column of air would be necessary to cause the barometer
to read 78 cm of mercury, if the atmosphere were of uniform density 1.2
kg/m3? The density of mercury is 13.53 x 103 kg /m3.
Question #20
The density of helium is 0.178 6 kg/m3 at S.T.P. If a given mass of helium at
S.T.P. is allowed to expand to 1.500 times its initial volume by changing the
temperature and pressure, compute its resultant density.