CHEM 6A
Exam 1.1 (250 pts)
Fall 2020
SHOW ALL OF YOUR WORK IN YOUR OWN HANDWRITING FOR CREDIT
Name: _________________________
Student Id #: __________________
1) (4 pts) Using the ruler provided, measure the arrow below to the correct number of significant
figures. Note: The ruler is not to scale.
2) (10 pts) What is the result of the following equation? Remember: Show work & check significant
figures
("## – &'"()
!(#.#""#
" + 7.258 𝑥 101( =
+ ,.-.#/& 0 "#! )
3) (16 pts) At liftoff, an orbiter and External Tank carry 3.1644 x 106 L of fuel. The density of the fuel
was 1.14 g/cm3, what is the mass of the fuel in Mg? Your answer needs to be in scientific notation
and have the correct number of significant figures for full credit.
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CHEM 6A
Exam 1.1 (250 pts)
Fall 2020
SHOW ALL OF YOUR WORK IN YOUR OWN HANDWRITING FOR CREDIT
4) (42 pts) Which of the following substances are classified correctly? Fill in the table with “Correct” or
“Incorrect” for each classification
Substance
Classification
I.
I2
compound
II.
chromium
nonmetal
III.
rubidium
Alkali metal
IV.
PO33-
pure substance
V.
Cup of hot tea
Aqueous solution
VI.
HCO3-
polyatomic anion
VII.
Cd
atom
VIII.
potassium nitride
binary covalent compound
IX.
Vanadium
Element
X.
Carbon
Main Group element
XI.
solution
heterogeneous mixture
XII.
aluminum
on the periodic table - element
in period 2 group IIA
XIII.
Noble gas
forms anion with 1- charge
XIV.
A substance whose
components cannot be
separated by physical
techniques
Homogenous mixture
Correct or Incorrect
5) (18 pts) Methane and oxygen react to form carbon dioxide and water.
a) (12 pts) What mass of carbon dioxide is formed if 5.17 g of methane react completely with
20.68 g of oxygen to produce 11.63 g of water?
b) (6 pts) What law or theory did you use to answer the question above?
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CHEM 6A
Exam 1.1 (250 pts)
Fall 2020
SHOW ALL OF YOUR WORK IN YOUR OWN HANDWRITING FOR CREDIT
6) (18 pts) Element X had three naturally occurring isotopes. Isotope 1 has a mass of 18.9769 amu with
a relative abundance of 84.35%. Isotope 2 has a mass of 19.9382 amu and isotope 3 has a mass of
17.9938 amu. The atomic weight of element X is 18.9515 amu. What is the percent abundance of
isotope 2?
7)
(12 pts) On the periodic table, Iodine’s atomic weight is less than the atomic weight of Tellurium.
However, Iodine has a higher atomic number than Tellurium. Explain how Tellurium could have a
smaller atomic number but a larger atomic weight.
8)
(24 pts) Use the compound K2C2O4 to answer the following two questions.
a) (8 pts) What is the formula weight of K2C2O4?
b) (8 pts) What is the mass percent of potassium in K2C2O4?
c) (8 pts) How many grams of potassium are present in a 4.193 g sample of K2C2O4?
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CHEM 6A
Exam 1.1 (250 pts)
Fall 2020
SHOW ALL OF YOUR WORK IN YOUR OWN HANDWRITING FOR CREDIT
(30 pts) Use the following description of a chemical reaction to answer the following two questions.
9)
•
Gaseous dinitrogen tetrahydride reacts with gaseous dinitrogen tetroxide to produce nitrogen gas
and gaseous water.
a) (15 pts) Write a balanced equation - remember to include phases.
b) (15 pts) Draw a molecular image of the reactant(s) and product(s) in the vessels below to
represent the balanced equation in the description above. Include an image/key if needed for
clarity.
→
10) (15 pts) Use the following description to write a complete balanced equation. Remember to include
phases.
• Aqueous potassium phosphate reacts with aqueous silver nitrate to form aqueous potassium
nitrate and solid silver phosphate.
11) (15 pts) Using correct terminology, describe the balanced equation below on a molecular level. To
earn full credit, remember to use the correct nomenclature for all compounds/molecules/
elements/etc. and include phases.
6 NH4ClO4 (s) + 8 Al(s) → 4 Al2O3(s) + 3 N2(g) + 3 Cl2(g) + 12 H2O(l)
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CHEM 6A
Exam 1.1 (250 pts)
Fall 2020
SHOW ALL OF YOUR WORK IN YOUR OWN HANDWRITING FOR CREDIT
12) (10 pts) What is the wavelength of light in nm that has a frequency of 6.86 x 1014? Would this
light be in the visible region of the electromagnetic spectrum?
13) (12 pts) What is the energy of 3.58 x 1012 photons of light that have a wavelength of
6.52 x 10-11m?
14) (24 pts) Use the following information below to answer the following questions.
•
An experiment is set up where a piece of chromium solid is placed in an evacuated glass tube
and is then hit with electromagnetic radiation of different energies. Cr(s) has a 𝜈! =
1.06 𝑥 10"# 𝑠 $"
a) (12 pts) What is the minimum amount of energy needed to emit an electron from the chromium
solid described above?
b) (6 pts) Electromagnetic radiation with a specific energy was used that produced photoelectrons.
Is it possible to increase the number of photoelectrons produced? If yes, how?
c) (6 pts) Electromagnetic radiation with a specific energy was used that produced photoelectrons.
Is it possible in increase the kinetic energy of those emitted photoelectrons? If yes, how?
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