AP Chemistry
Unit 1 Practice Problems
Name _________________________________
Date ____________ Class _____________
Determine the number of significant digits in each of the following
1. .93 mL __________
6. 1.008 mol
2.
340 g
3.
0.097atm __________
4.
5.
39.5 K
__________
__________
__________
8. 1000 mm = 1m
__________
9. 1
0.00760 m__________
_________
7. 27 test tubes
e–
=
-1.6x10-19
10. 541.005
C
m3
__________
__________
11. Complete the indicated operation and provide the final answer with the correct number of significant digits
Problem
Calculator answer
Answer rounded to the correct # of Sig.Figs.
a.
2.698 x 33.20 x 1.5611
b.
(3.2 x 103) (4.21x 102)
c.
3.00 x 154
d.
7.623 + 85.0 + 9.815
e.
23.6 - 16.1218
f.
(12.01 + 1.01 + 6)/101.4
g.
determine the mean of the following numbers: 8.2, 4.2, 11.8, 10.01
𝑚
Density calculations. Show all work. Always include units. Pay attention to sig. fig’s. 𝑑 =
𝑉
12. A block of lead has dimensions of 4.50 cm by 5.25 cm by 6.05 cm. The block has a mass of 1587 g. From this information
calculate the density.
13. The hydrogen stored in a large weather balloon weighs 13.558 g. What is the volume of this balloon if the density of hydrogen
is exactly 0.089 g/mL?
Student A
Student B
Student C
Trial 1
.002 g
.222 g
.010 g
Trial 2
.204 g
.212 g
.009 g
Trial 3
.104 g
.223 g
.011 g
Average
14. Which student has data that is the most accurate (accepted value is 0.010 g), explain.
15. Calculate the % error of student A. The accepted value is 0.010 g.
16. Which student has the lowest %deviation and thus best precision? Calculate each.
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17. Convert the following:
a. 345 nm  m
b.
3640 cm2  m2
c.
350 mL  L
d.
The average American farm is 435 acres. How many square miles is this? (1acre=43,560ft 2, 1 mile=5280ft)
18. Calculate the molar mass to 3 significant figures.
NaCl
H2O
Cl2
(NH4)2SO4
19. Use dimensional analysis to determine the following:
a. aluminum (MM = 27.0 g/mol, d = 2.70 g/cm3)
2.48 g Al mol
5.00 cm3 Al g
b.
carbon dioxide (MM = 44.0 g/mol, d = 1.82 g/L)
85.0 g CO2 L
3.15 mol CO2  g
C4H7NO4
CuSO4•5H2O
155 cm3 mol
3.22 L CO2  mol
20. The compound dioxin, C12H4Cl4O2 , which has been linked to birth defects. What is the percent composition of all the
elements in this compound?
21. Determine the empirical formula of ibuprofen, a common headache remedy. Analysis yields a percent composition of 75.7%
C, 8.80% H and 15.5% O.
22. A compound consists of 39.97% C, 13.41% H, and 46.62% N and has a molar mass of 60.10 g/mol. Determine the molecular
formula.
23. Which statements are consistent with Dalton’s atomic theory as it was originally stated? Why?
a. Sulfur and oxygen atoms have the same mass.
b. All cobalt atoms are identical.
c. Potassium and chlorine atoms combine in a 1:1 ratio to form potassium chloride
d. Lead atoms can be converted into gold.
e. An oxygen atom combines with 1.5 hydrogen atoms to form a water molecule.
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24. Describe an alpha particle.
25. Why did Rutherford assume that the atomic nucleus was positively charged?
26. Why does the “beam” in Thomson’s experiment bend when a magnet is placed near it?
27. How does Rutherford’s model of the atom explain why some of the alpha particles directed at the gold foil were deflected
straight back toward the source?
28. List three observations and three conclusions of Rutherford’s Gold Foil Experiment.
29. What is the electrical charge of an electron as determined by Robert Millikan?
Drop #
A
B
C
D
30. A chemist in an imaginary universe, where electrons have a different charge than they do in our
universe, performs the Millikan oil drop experiment to measure the electron’s charge. The
charge of several drops are recorded. What is the charge of the electron in this imaginary
universe?
Charge
-6.9 x 10-19 C
-9.2 x 10-19 C
-11.5 x 10-19 C
-4.6 x 10-19 C
31. A hydrogen filled balloon was ignited and 1.50 g of hydrogen reacted with 12.0 g of oxygen. How many grams of water vapor
formed? What law is this?
32. Two samples of carbon tetrachloride were decomposed into their elements. One sample produced 38.9 g of carbon and 448 g
of chlorine, and the other sample produced 14.8 g of carbon and 134 g of chlorine. Are these results consistent with the law of
definite proportions? Explain.
33. Complete the chart.
Z
A
# protons
# neutrons
# electrons
symbol
8
9 (neutral)
39
20
18
56
3+
26𝐹𝑒
(neutral)
84
36
64
29
Cu
31 3−
15𝑃
3
34. Calculate the average atomic mass of chlorine based on the spectrograph.
35. Magnesium has three naturally occurring isotopes with the following
masses and natural abundances. Sketch the mass spectrum of magnesium.
It would help to use a ruler. Properly label and scale each axis.
Isotope
Mg-24
Mg-25
Mg-26
Mass (amu)
23.9850
24.9858
25.9826
abundance %
78.99
10.00
11.01
36. Calculate the average atomic mass of Si, which consists of three isotopes listed below.
Isotope
Si-28
Si-29
Si-30
Atomic Mass
27.98
28.98
29.97
Abundance
92.20%
4.70%
3.10%
37. Identify each diagram as a pure substance or mixture. If it’s a pure substance, classify as element or compound.
(e)
(a)
(c)
(d)
(b)
38. Fill in the flow chart from the word bank:
(compound, element, heterogeneous, homogeneous,
matter, pure substance, mixture).
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39. Antimony has two isotopes: Sb-123 and Sb-121. Sb-121 has a mass of 120.9 amu and an abundance of 57.25 %. Antimony
has an average atomic mass of 121.75.
a. What is the abundance of Sb-123?
b.
What is the atomic mass of Sb-123?
40. The graph shown at the right illustrates the decay of
decays via positron emission.
a. What is the half-life of this decay?
88
42𝑀𝑜 ,
b.
What is the rate constant for this decay?
c.
What percent of the original sample remains after
12 minutes?
d.
How many minutes does it take the sample to go from
0.8 g to 0.5 g?
which
41. The half-life of radioactive S-35 is 88 days. Determine:
a. the rate constant.
b.
the number of days for the sample to be ¼ as radioactive (without a calculator).
c.
the number of days for the sample to be ¼ as radioactive (with a calculator).
d.
the percent that remain radioactive after 290 day.
42. Pu-236 has a half-life of 2.86 years. A sample initially contains 1.35 mg of Pu-236
a. what mass is present 5.00 years later?
b.
how long will it take the sample to decay to 0.100 mg?
43. Describe the mathematical relationship between wavelength and frequency.
44. As the frequency of light increases what happens to its energy?
45. What does it mean to say that an atom is in an excited state, what about ground state?
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46. Calculate the missing value.
Photon energy
Wavelength
3.25 x 10-18J
1.26 x 10-7m
6.60 x 10-19J
345 nm
47. A hydrogen electron transitions from n = 1 to n = 4.
a. What is the electron's energy at n = 1?
b.
What is the electron's energy at n = 4?
c.
Does the electron gain or lose energy in the transition?
d.
What is the change in energy of the electron?
48. A hydrogen electron transitions from n = 9 to n = 7.
a. What is the energy of the electron when n = 9.
b.
What is the energy of the electron when n = 7
c. What is the change in energy for the transition?
d.
Is energy absorbed or released during the transition?
e. What is the wavelength of the light emission?
49. Determine the energy of 1 mol of photons for each kind of light.
a. infrared radiation (1500 nm)
b.
visible light (500 nm)
c.
ultraviolet radiation (150 nm)
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