Download Honors Midterm - Stamford High School

Honors Chemistry Midterm
Name _____________________________
Review Questions (FORM A) with answers Chap 1-4, 25
1.
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Date _______________________
What constitutes the steps of a good experiment following the scientific method?
Clear purpose
Material and repeatable procedure
Experiment conducted with control, constants, independent variable, dependent variable
Data recorded and data analyzed
Conclusion related to data/error analysis
2) Chemical change is is when chemical bonds are broken
Ex. Rusting of iron, burning paper
3)
During a physical change some properties of a material change, but the composition
of the material does not change.
Examples of physical change are boiling, freezing, melting and condensing. Also breaking,
splitting, grinding, cutting and crushing.
4)
How can you separate a mixture? Paper chromatography can be used separate a mixture of inks,
distillation can be used to separate a mixture of liquid, filtration can be used to separate a solid from a
mixture.
What is conservation of mass in a chemical reaction? conservation of mass in a chemical
reaction – mass is conserved in chemical reaction/the mass may be rearranged but all the
mass is accounted for before and after the chemical reaction has taken place
5) Temperature conversions (C to K, K to C) Kelvin = Celcius + 273
6)
7)
What is the meaning of accuracy and precision?
What are the rules governing significant figures?
 All digits 1-9 inclusive are significant ex. 129 has 3 signigicant figures.
 Zeros between significant digits are always important. Ex. 5,007 has 4 signigicant figures
 Trailing zeros in a number are significant only if the number contains a decimal point ex: 100.0
has 4 significant figures, 100 has 1 significant figure.
 Zeros in the beginning of a number whose only function is to place the decimal point are not
significant. Ex. 0.0025 has 2 significant figures.
 Zeros following a decimal significant figure are significant. Ex. 0.000470 has 3 significant figures,
0.-47000 has 5 significant figures.
8)
How much does this graduated cylinder contain in the correct number of significant figures?
36.5 mL = volume of liquid in graduated cylinder
What is the formula for density? How is it like a heart shape? Density = mass/volume =
gram/mL = gram/cm3
9) What is a density column
10)
11)
12)
What is the charge on the helium nucleus above? +2
What is the charge on the whole atom of helium? neutral
How much does a proton weigh? A neutron weigh? A electron weigh?
14. Which subatomic particles are found in this helium nucleus? 2 protons and 2 neutrons
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15. What is an isotope? Isotopes of an element have different numbers of neutrons, they also have
different mass numbers
16) What are radioisotopes? Radioisotopes can be used to diagnose medical problems and, in some
cases, to treat diseases.
Background information:. How do you balance nuclear reactions
Sample Problem:
An atom of 138I53 undergoes β- decay and produces a β particle.
Solution:
Nuclear reactions need to have the sum of protons and neutrons the same on both sides of the
equation. The number of protons must also be consistent on both sides of the reaction.
β- decay occurs when a neutron converts into a proton and ejects an energetic electron called the beta
particle. This means the the number of neutrons, N, is reduced by 1 and the number of protons, A, is
increased by 1 on the daughter atom.
138
I53 → ZXA + 0e-1
A = number of protons = 53 + 1 = 54
X = the element with atomic number = 54
According to the periodic table, X = xenon or Xe
The mass number, A, remains unchanged because the loss of one neutron is offset by the gain of a
proton.
Z = 138
Substitute these values into the reaction:
138
I53 → 138Xe54 + 0e-1
Additional background information: How are half life calculations done? See page 806 in your textbook.
And the activities that we did in class.
The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams
would be left after 7.2 minutes has elapsed?
7.2 / 2.4 = 3 half-lives
(1/2)3 = 0.125 (the amount remaining after 3 half-lives)
100.0 g x 0.125 = 12.5 g remaining
16 (continued)Nuclear Chemistry. Define the following words and answer the
following questions.
b) Write the nuclear equation for the decay of Ir-192 that produces three things; a
nuclear isotope, a beta particle, and a gamma particle.
192
77
192
Ir →
78
Pt +
0
-1
e +00γ
c) Write the nuclear equation for the decay of platinum-199 that produces two things; a
nuclear isotope and a beta particle.
199
78
Pt →
0
-1
e + 199 79 Au
d) Krypton-76 undergoes electron capture
76
36
Kr + 0 -1 e →
76
35
Br
e) Write the symbols for an alpha particle, beta particle, and gamma ray
The positron is represented by the symbol:
Nuclear Radiation
NAME CHARGE SYMBOL
SHIELD
DISTANCE TRAVELED
alpha
positive
or  paper or clothing
beta
negative
or 
heavy clothing
2-3 m
gamma
neutral

lead or concrete
500 m
2-4 cm
f) If the half-life for the radioactive decay of zirconium-84 is 26 minutes and I
start with a 175 gram sample, how much will be left over after 104
minutes?
104/26= 4 half lives ,
(1/2)4 175 = 10.9 grams left of Zr-84
g) Why is it difficult to make a fusion reaction occur? It requires high temperature and
great pressure
17. Additional nuclear equation questions
Write “isotopic symbols” for:
238
92
Example:
U
alpha, 
4
2
beta, 
0
He
-1
e
___  ___
Nuclear Change:
gamma, 
0
0
γ
positron, 
0
+1
e
neutron, n
1
0n
___  ___
Complete these nuclear reactions:
a)
238
92
U 
b).
234
90
Th 
c).
234
91
Pa 
230
d).
220
86
Rn 
216
18.
234
90
Th +
234
91
Pa +
89
84
4
0
2
He
(alpha decay)
-1
e
( beta decay)
4
2
Ac +
Po +
4
2
He
He
( alpha decay)
( alpha decay)
Additional half life calculations
a.)Lr-257 has a half life of 8 seconds. What % of a sample will remain 32 seconds after it
is made?
1
2
3 half lives
8 seconds → 16 seconds → 24 seconds →32 seconds
(1/2)3 100 = 12.5 % of the sample will remain
b).A 64 gram sample of I-131 is tested after 40 days and is found to contain only 2 grams
of I-131. What is the half life of I-131?
1
2
3
4
5 half lives
64 → 32 → 16 → 8 → 4 → 2
40/5 = 8 days is one half life for I-131
19. Draw and label how alpha( , beta (, and gamma ( rays each travel when they pass through an
electric field. Use the diagram below to illustrate your answer. What direction does each particle
travel and what bending occurs.
What do we know about the charge of a beta, alpha and gamma particles?
What would happen it these particles were passed through a magnetic field
Carbon-14 has a half life of 5730 years. If you begin with a 100 gram sample of carbon-14 how much
will be left after 28650 years? Show your work and do not forget your units for full credit.
28650/5730 = 5 half lives have passed
(1/2)5 100 = 3.125 grams of C-14 is left