Chemistry 111
Exam 1, SPRING 2000
White Copy:
1. Pure substances must be either and element or a compound. The
only other options would be mixtures but by definition a mixture
is not a pure substance.
2. The three phases of matter are solid, liquid, and gas.
3. Pure substances which are composed of more than one atom
chemically bonded together are:
B) compounds
The key is bonded together. Single atoms are elements. Mixtures
have no bonds between the different parts.
4. A mixture in which the composition varies throughout is a:
C) heterogeneous mixture
Hetero is a greek term meaning "different". If the composition
varies then the composition is "different".
5. The SI unit of length is the:
D) meter
6. Which are the SI units of temperature, pressure, and mass,
respectively?
B) kelvin degrees, pascals, kilograms
7. Which of the following measurements contains four significant
figures?
A) 5.115 cm
8. Which of the following measurements is MOST precise?
A) 3.1416 kg
Precision comes from measuring more closely so the more digits
the more precise.
9. What is the result, with the proper number of significant
figures, when 6.005 m is multiplied by 22.31 m?
D) 134.0 m2
The result of the math is 133.97 so one needs to round off first
to 134. But we need 4 significant figures and thus add a
trailing zero with a decimal point to show precision.
10. Convert 224.0 mL to liters.
1 L
224.0 mL x --------- = 0.224 L
1000 mL
11. Convert 157 C to Kelvin
To convert from C to K requires adding 273, so the answer is
430 K
12. Water has a density of 1.00 g/cm3. What is the mass, in
kilograms, of 1.00 m3 of water?
g 100 cm 100 cm 100 cm 1 kg
1.00 --- x ------ x ------ x ------ x ------ = 1 x 103 kg
cm3 1 m 1 m 1 m 1000 g
13. The solubility of potassium chloride (should be bromide),
KBr, at 70 C is 48.3 g/100 g of water. Calculate the mass of KBr
which will dissolve in 250g of water at 70 C.
48.3 g X g
------ = -------
100 g 250 g
Cross multiply and solve for X.
X = 121 g = 1.21 x 102 g
14. At the melting point of a pure solid,
B) solid is changing to liquid
15. The nucleus of a lead atom, 20782 Pb, contains:
82 protons 'cause that's what the atomic number means and
207 - 82 = 125 neutrons because the atomic mass is the sum of
the masses of the protons plus the neutrons.
16. What is the symbol of an ion which has 20 protons and 18
electrons?
20 protons is Calcium, symbol, Ca
Since the # of electrons is less than the # of protons, the
ion has a positive charge. The difference is 2 so the proper
symbol for the ion is:
Ca2+
17. The periodic table is arranged by:
the number of protons in the nucleus.
18. Skipped nothing like this on final.
19. Name the elements whose symbols are
K P S Na
potassium phosphorus sulfur sodium
20. Name this compound: CaS
calcium sulfide
It is a sulfide because there is no oxygen with the sulfur. The
anion receives the -ide suffix when no oxygen is present.
21. The mass of Sr, strontium, is listed as 87.62. Which
answer best explains why the mass is not a whole number?
D) the mass shown in the periodic table is an average mass
based on natural isotopes.
22. Which of the following contains the same number of electrons
as neutrons?
The answer is A because:
Chlorine has 17 protons and 18 neutrons in the atomic state.
For the number of electrons to equal the number of neutrons,
chlorine must gain one electron. Thus Cl- has 18
electrons which equals the number of neutrons.
Answer B has 17 electrons and 18 neutrons, so they are not
equal.
Answer C has 18 electrons and 16 neutrons, again not equal.
Answer D has 18 electrons and 22 neutrons. Not equal.
Answer E has 15 electrons and 16 neutrons. Not equal.
23. Which of the following contains more electrons than neutrons?
See above for counts. The answer is C.
24. From the decomposition of a pure solid, we obtain a solid and
a gas, each of which is a pure substance. We can conclude that:
A) Correct, elements cannot be decomposed.
B) WRONG, we said it was pure.
C) WRONG, there are many pure substances which are solids or
gases.
D) WRONG, there are many pure substances which are solids
and gases which are not elements.
E) WRONG, there are solid elements and gaseous compounds.
This was an effort in critical thinking.
25. Which of the following lists calcium, carbon, chlorine,
sulfur, and silicon in the same order as these names?
B) Ca, C, Cl, S, Si
26. The correct formula for potassium phosphate is:
Potassium is in Group 1 so it carries a charge of +1.
Phosphate ion is PO43-. To form a compound, the charges must
balance. So we need 3 + to balance 3 -.
D) K3PO4
27. In Al2O3, what is the charge on the oxygen ion?
Oxygen ion ALWAYS has a charge of 2-. The question was NOT
plural "ions".
28. Which of the following elements has the largest atomic mass?
Look in the periodic table.
B) tin (Sn)
29. How many elements are there in Group 16 of the periodic
table?
C) 5, just count down the column.
30. Magnesium metal is reacted with oxygen gas and a white
powder, magnesium oxide, is produced. If 3.56 g of Mg reacts
with 7.00 g of oxygen to produce 5.93 g of magnesium oxide and
some unreacted oxygen, what is the mass of oxygen that has
reacted with magnesium?
B) 2.37 g
31. What is the formula of the hydroxide ion?
A) OH-
32. What is the formula of iron(III) chloride?
The III means the Fe has a charge of 3+. Chloride has a
charge of 1- so it takes 3 Cl- to balance one Fe3+.
B) FeCl3
33. The formula of acetic acid is CH3CO2H. How many carbon atoms
are in on acetic acid molecule?
Just count how many are in the formula since formulas describe
the composition of the molecule.
B) 2
34. How many moles of hydrogen atoms are in 0.50 mol of acetic
acid, CH3CO2H?
The are 4 hydrogen atoms in each acetic acid molecule. Since
moles are molecules times Avogadro's Number, the proportion stays
the same. Thus
4 x 0.50 mol = 2 mol
35. What is the molar mass of acetic acid, CH3O2H?
2 x 12 = 24
4 x 1 = 4
16 x 2 = 32
----
total = 60
The Atomic Numbers represent amu values for a molecule and g measurements
for moles so the answer is:
D) 60 g/mol
36. What is the mass in grams of 1.0 x 108 atoms of iron (Fe)?
The mass of 1 atom is: 55.847 g
----------- = 9.28 x 10-23
6.02 x 1023
because there are Avogadro's Number of atoms in a mole of Fe
(or any substance) and the mass of one mole of Fe is 55.847
g.
The mass of 1.0 x 108 atoms is then:
1.0 x 108 x 9.28 x 10-23 = 9.29 x 10-15 g
The answer is D
37. A tablet of aspirin contains 0.500 g of aspirin (molar mass
= 180 g/mol). How many moles of aspirin are in the tablet?
Ratio: 0.500 g 180 g
--------- = ---------
X mol 1 mol
180X = 0.5
X = 0.00278 mol
The answer is C
38. What is the mass in grams of a single molecule of water?
The mass of a mole of water is 18.02 g. There are Avogadro's
Number of molecules in a mole of water. We want the mass in one
molecule so:
18.02 g
-------------- = 2.99 x 10-23 g/molecule
6.02 x 1023
The answer is D
39. What is the mass of 5.00 millimoles of NaCl (58.44 g/mol)?
A millimole may seem confusing BUT remember milli = 10-3
so a millimole is 10-3 mole.
5.00 millimoles converts to 5.00 x 10-3 mol
Next multiply by the mass of one mole:
5.00 x 10-3 mol x 58.44 g/mol
0.292 g
40. Ammonium nitrate (NH4NO3) is used as a fertilizer. How many
grams of nitrogen atoms are in 1.00 mol of NH4NO3?
There are 2 N in each NH4NO3 so:
2 x 1.00 mol = 2 mol of N
Molar mass of N is 14 g/mol so:
2 mol N x 14 g/mol = 28 g N