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Home , Isotopes of cerium

CHEM 1A: Midterm Exam 1--Spring 2015 Name:______

INSTRUCTIONS: On the FRONT and BACK of the scantron, fill out your name and 7-digit student ID. Fill in this information from left to right in the provided fields, and BUBBLE IN the values on the scantron. 1 point will be deducted from your exam grade for incomplete or erroneous filling of the scantron. MULTIPLE CHOICE QUESTIONS: 1. How many significant figures does this number have: 0.0005900 x 10-1 ? A. 2 B. 4 C. 5 D. 6 E. 8 2. The answer to the calculation below should be reported to how many significant figures? (ퟕퟓ.ퟗퟓퟎ−ퟕퟓ.ퟓퟓ) = ______ퟕퟓ.ퟓퟓ A. 1 B. 2 C. 3 D. 4 E. 5 푱 3. Using dimensional analysis, simplify these units: = ______(풎/풔)ퟐ A. kg·m2/s2 B. kg·m2/s C. kg·m/s2 D. kg·m/s E. kg

4. Convert 19.5 g·cm-3 to kg/m3. 10 3 A. 1.95 x 10 kg/m B. 1.95 x 105 kg/m3 C. 1.95 x 104 kg/m3 3 3 D. 1.95 x 10 kg/m E. None of the above.

5. Convert 36 x 10-6 mg to ng. A. 3.6 x 107 ng 1 B. 3.6 x 10 ng C. 3.6 x 10-11 ng D. 3.6 x 10-17 ng E. None of the above.

6. How many cubic micrometers (µm3) are in 1 cubic meter (m3)? A. 1 x 106 µm3 = 1 m3 B. 1 x 10-6 µm3 = 1 m3 C. 1 x 109 µm3 = 1 m3 D. 1 x 1018 µm3 = 1 m3 E. 1 x 10-18 µm3 = 1 m3 7. How many grams of atoms are present in 4.42 moles of nickel metal (Ni)? Information that MIGHT be useful: Density of nickel = 8.908 g/cm3 A. 2.59 x 102 g B. 39.4 g C. 29.2 g D. 0.496 g E. 0.0750 g

8. How many TOTAL ATOMS are present in 0.878 moles of CH4?

3 Information that MIGHT be useful: Density of CH4 = 0.66 kg/m

A. 1.06 x 1023 atoms B. 2.64 x 1024 atoms C. 1.32 x 1023 atoms D. 1.46 x 10-24 atoms E. None of the above

9. What is the volume (in cm3) of 453 mg of metal?

Information that MIGHT be useful: Density of titanium = 4.43 g/cm3

A. 0.102 g B. 2.01 g C. 4.89 g D. 9.78 g E. 21.7 g

10. How many molecules are present in 440 grams of dioxide? A. 1.2 x 1027 B. 6.0 x 1024 molecules C. 1.8 x 1024 molecules 23 D. 6.0 x 10 molecules E. None of the above.

11. How many atoms are in 9.65 cm3 of (Au)?

Information that MIGHT be useful: Density of gold = 19.3 g/cm3

A. 2.95 x 1022 atoms B. 5.69 x 1023 atoms C. 5.93 x 1025 atoms D. 6.11 x 1021 atoms E. 1.57 x 10-24 atoms

12. Which sample below contains the LEAST number of ATOMS?

A. 4.00 g of diatomic (H2) B. 4.00 g of C. 12.0 g of D. 44.0 grams of carbon dioxide E. All of the samples above contain the same number of atoms. 13. How do (I) and copper (II) differ? A. Different number of protons B. Different number of neutrons C. Different number of electrons D. Different atomic number E. Different masses

14. How do copper-63 and copper-65 differ? A. Different number of protons B. Different number of neutrons C. Different number of electrons D. Different atomic number E. Different charges

15. A substance is composed of 1.5999 grams and 0.7005 grams of an unknown element (X). Assuming the

formula of this unknown substance is XO2 & using the relative masses, what is a possible identity of element X? A. (W) B. (Sn) C. Titanium (Ti) D. (S) E. (N)

16. Naturally occurring (Sr) consists of the four stable below and has an average of 87.62 amu. Based on only this data, select the that is MOST abundant, or choose E. if insufficient information is provided to make a conclusion.

Strontium Isotope Isotopic Mass (amu) A. Strontium-84 83.9134 B. Strontium-86 85.9092 C. Strontium-87 86.9088 D. Strontium-88 87.9056 E. Cannot determine from information provided.

17. Naturally occurring (Cr) consists of the four stable isotopes below and has an average atomic mass of 52.00 amu. Based on only this data, select the isotope that is MOST abundant, or choose E. if insufficient information is provided to make a conclusion.

Chromium Isotope Isotopic Mass (amu) A. Chromium-50 49.9460 B. Chromium-52 51.9405 C. Chromium-53 52.9406 D. Chromium-54 53.9389 E. Cannot determine from information provided.

18. Naturally occurring (Ce) consists of the four stable isotopes below and has an average atomic mass of 140.12 amu. Based on the fact that Cerium-140 is the most abundant of these four isotopes (with a percent abundance of 88.45%), which isotope must be the SECOND most abundant? Select E. if insufficient information is provided to make a conclusion.

Cerium Isotope Isotopic Mass (amu) MOST ABUNDANT  Cerium-140 139.9054 A. Cerium-136 135.9072 B. Cerium-138 137.9060 C. Cerium-142 141.9092 D. Ce-136 & Ce-138 are tied for the second most abundant isotopes of Cerium. E. Cannot determine from information provided.

19. Which form of radiation is LEAST penetrating? A. Alpha (α) particles B. Normal beta (β-) particles C. Gamma (γ) rays D. B & C are equally penetrating. E. All of the above are equally penetrating.

232 20. What final isotope would be produced if -232 ( 90푇ℎ) underwent one alpha decay, followed by one beta decay, followed by one gamma decay? A. -228 B. -227 C. -230 D. -228 E. None of the above.

21. Which pair reacts to form ionic compounds? A. (K) and (Be) B. (Fe) and (Os) C. Nitrogen (N) and Oxygen (O) D. Copper (Cu) & (Se) E. None of the above would form ionic compounds.

22. Which pair reacts to form covalent compounds? A. (Li) and (F) B. (Br) & Sulfur (S) C. (Ba) and (Tl) D. (In) and (Te) E. None of the above would form covalent compounds.

23. What must the charge on X be in the ionic compound: X(CrO4)3? A. +1 B. +2 C. +3 D. +4 E. +6 24. Consider the formula of aluminum sorosilicate as Al2Si2O7. Based on this information, what is the charge (x) on x one of the polyatomic ions, sorosilicate: Si2O7 ? A. x = -2 B. x = -3 C. x = -4 D. x = -6 E. x = -14

25. What is the approximate molar mass of (NH4)2SO4 to three significant figures? A. 160. g/mol B. 132 g/mol C. 118 g/mol D. 114 g/mol E. None of the above.

26. Which electron transition below would emit the SHORTEST wavelength of light? (where ni is the initial state and

nf is the final state)

A. ni = 10 → nf = 2

B. ni = 10 → nf = 4

C. ni = 4 → nf = 10

D. ni = 4 → nf = 2

E. ni = 2 → nf = 4

27. Consider the two electromagnetic waves shown to the 15 right. If the top wave has a frequency of 9.5 x 10 Hz, how would the bottom wave compare? A. The bottom wave would have a longer wavelength. B. The bottom wave would have the same wavelength. C. The bottom wave would have a lower frequency. D. The bottom wave would have a higher frequency. E. The bottom wave would have the same frequency.

28. What is the frequency of light emitted from a laser beam operating at 532 nm? A. 1770 Hz B. 5.64 Hz C. 0.000564 Hz 14 -1 D. 5.64 x 10 s E. 1.77 x 10-15 /s

29. Assume that light of 950 nm is NOT capable of ejecting electrons from the surface of a metal. What would light at 925 nm do? A. It also will NOT cause electrons to be ejected. B. It WILL cause electrons to be ejected.

C. Cause a transition from ni = 10 → nf = 3

D. Cause a transition from ni = 3 → nf = 10 E. Cannot determine from information provided. The work function of the metal would need to be specified. 30. Four different unknown metals (1, 2, 3, & 4) were exposed to light of the SAME wavelength. Given the work function of each metal below, which metal would eject electrons with the LOWEST velocity? A. Metal 1: Ф = 612 kJ/mol B. Metal 2: Ф = 472 kJ/mol C. Metal 3: Ф = 987 kJ/mol D. Metal 4: Ф = 504 kJ/mol E. Cannot determine from information provided.

31. The energy required to eject an electron from an unknown metal is Ф = 3.31 x 10-20 J/electron. Calculate the MAXIMUM wavelength of light that can eject an electron from this metal. A. 6.00 x 10-6 m B. 1.67 x 1021 m C. 6.00 x 10-22 m D. 1.67 x 105 m E. None of the above.

32. If an electron and a proton travel at the SAME velocity, which has the shorter De Broglie wavelength? A. The electron B. The proton C. Neither, they both have equal De Broglie wavelengths. D. Cannot determine from information provided; it depends on the velocity.

33. The uncertainty in the velocity (Δv) of a football thrown by Russel Wilson during the superbowl is ±5.27 x10−6 m/s. If the football has a mass of 0.40 kg, what is its uncertainty in position (Δx)? A. 2.50 x 10-29 m B. 2.50 x 1039 m C. 3.99 x 1028 m D. 8.99 x 1039 m E. ZERO—the position is known with complete certainty.

FREE RESPONSE QUESTIONS:

Please read each question carefully. Report all final answers in PROPER scientific notation. SHOW YOUR WORK FOR FULL CREDIT.

1. The mass composition of two different hydrocarbons is reported below. If the first substance has a formula of

C2H6, propose a formula for the unknown that is consistent with the experimental data below.

Compound Mass of Carbon (g) Mass of Hydrogen

C2H6 6.00 1.50

Unknown 8.58 1.42

2. Fill in the table below following the systematic rules of nomenclature. FORMULA SYSTEMATIC NAME

diphosphorus pentaselenide

H2Se

Copper (II) permanganate

Cl2O7

tungsten (IV) oxalate

HClO4

hydrobromic acid

(NH)4PO3

dichromate

Ti(SO4)2 3. Fill in the table below. If an element is charged, be sure to write the total charge with the element symbol. Element or Ion Number of PROTONS Number of NEUTRONS Number of ELECTRONS

121Sb3-

92 142 90

4. Write balanced nuclear reactions from the decay events described below. Be sure to include the atomic number, mass number, and element symbol for each isotope involved in the reaction.

A. Write the reaction for -32 undergoing beta (β) decay. This radioactive form of phosphorus is used in treating leukemia.

B. A new cancer treatment, targeted alpha therapy (TAT), uses alpha decay to kill cancer cells. -212 is attached to a carrier molecule, which when ingested travels to the site of the tumor and gives off alpha radiation, killing all cells in the area. Write the reaction for Lead-212 undergoing alpha decay.

5. In intergalactic space where the density of hydrogen gas is low, hydrogen atoms can exist in excited states where n > 100. What is the wavelength of light produced (in nanometers) when an electron in hydrogen falls from n = 250 to n = 5?

IMPORTANT: On the next 2 pages, choose ONLY ONE of the questions below to answer (either #6 or #7); the other question will not be graded. Circle the question you want graded, and put an X through the question you don’t want graded.

6. Consider the electron energy level diagram shown below for an unknown element. A. On this energy diagram, draw all possible electron relaxations given these quantum levels.

B. Based on your answer from part A, how many unique wavelengths of light would you expect to observe in the emission spectrum for this substance? Explain your reasoning by predicting the approximate emission spectrum.

Assume the change in energy from quantum numbers n = 5 to n = 4 is the same as the transition from n = 2 to n = 1.

Number of Unique Wavelengths = ______

INCREASING FREQUENCY

INCREASING WAVELENGTH

7. If light of 32.4 nm ejects electrons from the surface of a metal with a velocity of 3.59 x 106 m/s, calculate the work function of the metal in Joules per electron (J/e-).

EXTRA CREDIT:

8. Viruses are significantly smaller than human cells, bacteria, and other cellular organisms. The tobacco mosaic virus, which infects a wide range of plants, has a mass of 6.8 x 10-20 kg and dimensions of 300 nm by 18 nm.

A. Assuming a tobacco mosaic virus is traveling at 4.9 µm/s, calculate its De Broglie wavelength in nanometers (nm).

Tobacco Mosaic Virus

B. If the uncertainty in the velocity of the tobacco mosaic virus is ±0.29 µm/s, calculate the uncertainty in its position (Δx) in nanometers.

C. Would you expect a tobacco mosaic virus to behave quantum mechanically or classically? Explain your reasoning using the De Broglie wavelength from part A, the uncertainty from part B, and the dimensions of the virus.

REFERENCE INFORMATION

1 mile = 1.609 km 1 in = 2.54 cm 1 m = 3.28 ft

1 kg = 2.204 lbs. 1 gal = 3.785 L Density = Mass/Volume

ퟏ 풎풐풍풆 = ퟔ. ퟎퟐퟐퟏퟒퟏ 풙 ퟏퟎퟐퟑ 풑풂풓풕풊풄풍풆풔

푐 = 휆휈 where 푐 = 2.9979 푥 108 푚 ∙ 푠−1

푬 = ℎ휐 where ℎ = 6.626 푥 10−34 퐽 ∙ 푠

ℎ 1 1 1 −2 −1 휆퐷푒 퐵푟표𝑔푙𝑖푒 = = 푅퐻 ( 2 − 2) where 푅퐻 = 1.097 푥 10 푛푚 푚∙v 휆푝ℎ표푡표푛 푛푓 푛𝑖

퐸푝ℎ표푡표푛 = Φ + 퐾퐸 where Φ = work function

1 퐾퐸 = 푚 ∙ v2 where 푚 = 9.109 푥 10−31 푘𝑔 2 푒푙푒푐푡푟표푛