Chem 127, Exam I
October 4, 2001
Name
I. (40 points)
A. (14 points) Fill in the empty boxes with the appropriate symbol, number, word or
charge.
Nuclear symbol
39
58
K
Protons
Ni2+
28
30
8
(name of subatomic
particle)
Electrons
10
Mass Number
16
Atomic Number
Net Charge
0
2–
1
Chem 127, Exam I
October 4, 2001
Name
B. (6 points) Determine whether the statements given below are true or false. Write Y if
the statement is true, and N if the statement is false in the blanks provided. Do not
use T or F.
1. Neutrons have neither mass nor charge.
2. Isotopes of an element have an identical number of protons.
3. C–14 and N–14 have identical neutron to proton (n/p+ ) ratios.
4. The vertical columns in a periodic table are referred to as ”groups”.
5. When an atom loses an electron, it becomes positively charged.
6. An anion is a negatively charged ion.
C. (10 points) Write the formulas of the following compounds.
1. Carbon dioxide
2. dinitrogen pentoxide
3. hydrogen peroxide
4. manganese(II) fluoride
5. potassium chlorite
D. (10 points) Write the names of the following compounds:
1. HBr (g)
2. NH3
3. P4 S10
4. Fe(NO3 )3
5. KClO4
2
Chem 127, Exam I
October 4, 2001
Name
II. (25 points) SHOW ALL WORK IN A LOGICAL WAY in the space provided. Work done
elsewhere will not be considered. Answers without work, no matter how trivial the
problem may seem, will receive no credit. Place your answers in the blank provided.
Use appropriate units and significant figures throughout.
A. The metric prefix micro (µ) represents the factor 10−6 . How many µm are there in
one cm?
B. The solubility of table sugar (sucrose) in water at 20◦ C is 2.10 x 102 g sucrose/100 g
of water. If 55.0 g of sugar were added to 20.0 g of water at 20◦ C, how many grams
of sugar would remain undissolved?
3
Chem 127, Exam I
October 4, 2001
Name
C. A solution is prepared from 25.0 mL of ethyl alcohol (d = 0.780 g/mL) and 35.0 mL of
water (d = 1.00 g/mL). The volume of the solution is 58.0 mL.
1. What is the density of the solution?
2. What is the mass percent of ethyl alcohol in the solution?
D. The area of the 48 contiguous states is 3.02 x 106 mi2 . Assume that these states are
completely flat (no mountains and no valleys). What volume of water, in liters, would
cover these states with a rainfall of two inches? 1 ft3 = 28.32 L and 5280 ft = 1 mi.
4
Chem 127, Exam I
October 4, 2001
Name
III. (60 points)
A. (15 points) Answer the questions below, using LT (for is less than) , GT (for is greater
than) , EQ (for is equal to) , or MI (for more information required) in the blanks
provided.
1. The mass (to 3 significant figures) of 6.022 x 1023 atoms of Na
(1)
23.0 g.
2. Boron has 2 isotopes, B–10 (10.01 amu) and B–11 (11.01 amu). The abundance
of B–10 (2) the abundance of B–11.
3. If S–32 were assigned as the standard for expressing relative atomic masses
and assigned an atomic mass of 10.00 amu, the atomic mass for H would be
(3) 1.00 amu
4. When phosphine gas, PH3 , is burned in oxygen, tetraphosphorus decaoxide
and steam are formed. In the balanced equation (using smallest whole number
coefficients) for the reaction, the sum of the coefficients on the reactant side is
(4) 7.
5. The mass (in grams) of one mole of bromine molecules is
(5)
79.90.
B. (5 points) An oxide of titanium is made up titanium (Ti) and oxygen atoms. It is
determined that the oxide is 40.06% oxygen. What is the simplest formula for the
oxide?
5
Chem 127, Exam I
October 4, 2001
Name
C. (20 points) Consider hydrazine, N2 H4 .
1. What is its molar mass in grams?
2. What is its simplest formula?
3. How many moles are there in 2.65 g of hydrazine?
4. How many grams of hydrazine are there in 12.01 x 1026 molecules of hydrazine?
5. How many hydrogen atoms are there in 1.769 mol of hydrazine?
6. How many grams of hydrogen can be obtained from 100.0 g of hydrazine?
6
Chem 127, Exam I
October 4, 2001
Name
D. (8 points) For the reaction
3 Br2 () + I2 (s) → 2 IBr3 (s)
How many grams of IBr3 (M = 366.6 g/mol) can be obtained from 5.00 g of Br2
(M = 159.8 g/mol)?
E. (12 points) Consider the following reaction.
2 BF3 (aq) + 3 H2 O (g) → B2 O3 (s) + 6 HF (g)
In an experiment 7.2 mol of BF3 reacts with 8.9 mol of H2 O.
1. What is the theoretical yield of B2 O3 (in moles)? (Assume 100% yield.)
2. How many moles of the excess reactant remain? (Assume 100% yield.)
3. If the reaction has a 73% yield, what is the actual yield of B2 O3 (in moles)?
7
Chem 127, Exam I
October 4, 2001
Name
IV. (25points)
A. (15 points) In each of these questions, PRINT in capital letters (i.e. A, B, C, etc. and
not a, b, c, etc.) on the blanks at the left the letter of that choice which is the best
answer. Circled letters will not be considered. There is no penalty for guessing.
Answer the following questions by referring to the graph of the solubility data for
CuSO4 · 5 H2 O and KNO3 printed on a sheet at the back of this exam. You may tear
out that sheet.
Consider a solution formed with 50.0 g of CuSO4 · 5 H2 O, 50.0 g of KNO3 and only
50.0 g of water.
1. The solution is heated to 60°C. Choose the statement that best describes this
solution:
A. This is a clear solution.
B. This is a cloudy solution.
C. This is a clear solution with only CuSO4 · 5 H2 O crystals forming on the bottom.
D. This is a clear solution with only KNO3 crystals forming on the bottom.
E. Crystals of both salts form.
2. The solution is cooled to 25°C. Choose the statement that best describes this
solution:
A. This is a clear solution.
B. This is a cloudy solution.
C. This is a clear solution with only CuSO4 · 5 H2 O crystals forming on the bottom.
D. This is a clear solution with only KNO3 crystals forming on the bottom.
E. More crystals are formed from CuSO4 · 5 H2 O than from KNO3 .
F. None of the above is true.
3. Fifty grams of KNO3 are added to the original solution to bring the total
composition to 100.0 g KNO3 , 50.0 g CuSO4 · 5 H2 O and 50.0 g of water. The
solution is heated to 85◦ C. Choose the statement that best describes this solution:
A. This is a clear solution.
B. This is a cloudy solution.
C. This is a clear solution with only CuSO4 · 5 H2 O crystals forming on the bottom.
D. This is a clear solution with only KNO3 crystals forming on the bottom.
E. More crystals are formed from KNO3 than from CuSO4 · 5 H2 O.
F. None of the above is true.
8
Chem 127, Exam I
October 4, 2001
Name
B. (5 points) Write the answers on the blanks provided on the left.
(1)
What is the name of the value in chromatography
obtained in the following way:
distance traveled by ion/distance traveled by solvent
(2)
What is the color of CuSO4 · 5 H2 O?
(3)
What is the color of SiC?
(4)
What is the name of the special flask used in the
density experiment?
(5)
What is the name of the funnel used to fiter a
solution using a vacuum line?
C. (5 points) A sample of an alloy is placed in a flask with a volume of 50.00 mL. The
flask weighs 57.0234 grams empty. The flask weighs 86.7894 g when weighed with
the alloy. The flask + alloy + water weighs 120.8604 g. Take the density of water to
be 1.000 g/mL. What is the density of the alloy?
9
Chem 127, Exam I
October 4, 2001
Name
BONUS (15 points) All or nothing.
The bonus should be done only after you have completed the main part of this exam and
checked your work for errors. The time alloted for this exam does not include time for the
bonus.
Consider 45.00 g of a saturated solution at 30◦ C made up of salt Y and water. The solution
contains the maximum amount of salt that can be dissolved. The solubility of salt Y in water
at 30◦ C is 22.04 g Y/100 g water. How much water is present in the solution?
10