Chemistry Workbook 1-1A - Saddleback .Chem 1A Dr. White 1Fall 2013 ! Chemistry Workbook 1: Problems

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  • Chem 1A Dr. White Fall 2013 1

    Chemistry Workbook 1: Problems For Exam 1

    Section 1-1: Significant Figures How many significant figures do the following numbers have? 1) 1234 _____ 2) 0.023 _____ 3) 890 _____ 4) 91010 _____ 5) 9010.0 _____ 6) 1090.0010 _____ 7) 0.00120 _____ 8) 3.4 x 104 _____ 9) 9.0 x 10-3 _____ 10) 9.010 x 10-2 _____ 11) 0.00030 _____ 12) 1020010 _____ 13) 780. _____ 14) 1000 _____ 15) 918.010 _____ Solve the following mathematical problems such that the answers have the correct number of significant figures: 16) 334.54 grams + 198 grams = ________ 17) 34.1 grams / 1.1 mL = _______ 18) 2.11 x 103 joules / 34 seconds = ______ 19) 0.110 meters 0.10 m = ______ 20) 349 cm + 1.10 cm + 100 cm = ________ 21) 450 meters / 114 seconds = _____ 22) 298.01 kilograms + 34.112 kilograms = _____ 23) 84 m/s x 31.221 s = ________ 24) (5.159 + 82.3) x (0.024 + 3.00) = _____ 25) 2.34 x 4.4391 / 3.465 = _____ 26) (0.00015 x 54.6) + 1.0020 = _____ 27) Read the following measurements

    Section 1-2: Dimensional Analysis and Significant Figures Round numerical answer to contain the correct number of significant digits. If the answer is smaller than 0.01 or larger than 1000, use scientific notation

    1. Convert 0.0456 nm to cm.

    2. Convert 0.03030 kg to ng.

    3. Convert 72.6C to F.

    4. Convert 14.5F to Kelvin.

    5. A piece of metal alloy weighs 12.0000g and contains iron, cobalt, and nickel. What is the weight of the nickel is the iron and cobalt are determined to be 11.53g and 0.1233g respectively?

    6. If 18.57 g of water is combined with 15.3 mL of water, what is the total volume? The density of water is 0.998 g/mL.

    7. The density of iron is 7.20 g/cm3. Calculate the mass, in kilograms, of 7.6 x 103 cm3 or iron?

    8. What is the volume, in liters, of 544 g of iron? The density of iron is 7.20 g/cm3. (Recall that one cm3 is exactly 1 mL).

  • Chem 1A Dr. White Fall 2013 2

    9. Light travels at 186,000 miles per second (3 sig figs). How many kilometers does light travel in one day?

    10. The speed of sound in water is 4.7 x 103 feet per second. How long, in minutes, does it take for sound to travel 19,000 km?

    11. A solution contains 4.52 g of sugar per liter. What volume of the solution, in liters is needed to supply 2.0 kg of sugar?

    12. A solution contains 144.1 mg of NaCl per liter. What volume of the solution, in milliliters, is needed to supply 27.8g of NaCl?

    13. A cylindrical redwood tree is 255 ft tall and 16 ft in diameter. The density of the redwood is 0.9 g/cm3. Calculate the mass of the tree in pounds. (Vcylinder = r2h)

    14. The density of Saran Wrap is 0.80 g /cm3. Calculate the mass, in grams, of a roll that is 2.00 x 102 ft long, 12.00 inches in diameter. (assume it is a cylinder).

    15. What is the volume, in cubic centimeters, of a rectangular block whose dimensions are 3.88 in by 5.0 in by 36 in?

    16. What is the diameter, in millimeters, of a red blood cell whose volume is 9.0 x 101 m3? Assume that the cell is spherical (Recall that the volume of a sphere is V=4/3r3).

    17. A piece of metal with mass 34.65 is placed into a 50-mL graduated cylinder partially filled with water, raising the water level from 22.5 mL to 30.7 mL. What is the density of the metal?

    18. The mass of a vial is 18.41 g. After a 10.00 mL sample of methanol is pipetted into it, the vial and sample have a mass of 26.34 g. Calculate the density of methanol. Remember that the volume of a pipet is accurate to 0.01 mL.

    19. The mass of a vial is 28.20 g. After five milliliters of benzene is pipetted into the vial, the vial and its contents have a mass of 32.55 g. What is the density of benzene?

    20. If 50 mL of water is pipetted into a flask weighing 90.45 g, what will be the total weight of the flask with the water? The density of water is 0.998g/mL.

    Section 1-3: Atomic Structure Intro

    1. In the early 1900s a common model for the structure of the atom was the plum pudding model. In this model, negatively charged electrons reside in the atom surrounded by a diffuse, continuous medium of positive charge (like plums in a pudding, or for a more modern analogy, like chocolate chips in a cookie).

    (a) In 1911 Earnest Rutherford carried out an experiment that changed the way we view the atom. Briefly describe this gold foil experiment.

    (b) How is the plum pudding model inconsistent with Rutherfords experimental findings? Approach this by considering the plum pudding hypothesis, and then predict what you would have expected to happen in Rutherfords experiment if the plum pudding model was true.

    (c) Draw a picture of Rutherfords model of the atom. Use your picture to describe why most of the alpha

    particles pass through the gold foil in Rutherfords experiment.

  • Chem 1A Dr. White Fall 2013 3 2. Atoms X, Y, Z, and R have the following nuclear compositions:

    Which two are isotopes? Explain. 3. Fill in the following table for neutral atoms of the given isotopes.

    4. Silicon, which makes up about 25% of Earth's crust by mass, is used widely in the modern electronics

    industry. It has three naturally occurring isotopes, 28Si, 29Si, and 30Si. Calculate the atomic mass of silicon. (28.09 amu) Isotope Isotopic Mass (amu) Abundance % 28Si 27.976927 92.23 29Si 28.976495 4.67 30Si 29.973770 3.10

    Section 1-4: Wave and Particle Behavior

    1. Consider the following types of electromagnetic radiation: i) microwave ii) ultraviolet iii) radio waves iv) infrared v) x-ray

    a) arrange them in order of increasing wavelength b) arrange them in order of increasing frequency c) arrange them in order of decreasing energy d)

    2. In the diagram below, draw in each of the following. Make sure you label each new wave! a) A wave with shorter wavelength b) A wave with smaller frequency c) A wave with the same wavelength and frequency but less amplitude.

    3. Some of the new cordless phones are said to operate at 900.MHz. Calculate the wavelength and energy of these waves.

  • Chem 1A Dr. White Fall 2013 4 4. Cobalt-60 is a radioactive isotope used to treat cancers of the brain and other tissues. A gamma ray emitted by an atom of this isotope has a wavelength of 9.32 x 10-13 m.

    a. What is this wavelength in nm? b. What is the frequency of this light in Hz c. Does radiation with = 242 nm have greater or lesser energy than the radiation emitted by the gamma ray above? What about radiation with = 2200 (1 = 1 x 10-10 m)? (You shouldnt need to do calculations to answer these questions)

    5. Molybdenum metal will eject an electron if it absorbs a photon with an energy of at least 7.22 x 1019 J. If Mo is irradiated with UV light with a wavelength of 120. nm, could an electron be ejected? 6. Calculate the de Broglie wavelengths for (a) an electron with a speed of 3.0 x 106 m/s (mass of an electron is 9.109 x 1031 kg) and (b) a 12 g bullet whose speed is 200 m/s. 7. Two objects are moving at the same speed. Which (if any) of the following statements about them are true?

    a. The wavelength of the heavier object is longer. b. If one object has twice as much mass as the other, its wavelength is one-half the wavelength of

    the other. c. Doubling the mass of one of the objects will have the same effect on its wavelength as does

    doubling its speed.

    8. The speed of the electron in the ground state of the hydrogen atom is 2.2 x 106 m/s. What is the wavelength of the electron? 9. At what speed must a human weighing 150. lb. be traveling in order to have a wavelength in the visible region, say at 650 nm? Does it seem likely that a human would attain such a speed? (1 kg = 2.20 lb) 10. Identify the following transitions as either absorption or emission:

    a) n = 3 n = 1 b) n = 6 n = 4 c) n = 1 n = 5 d) n = 1 n = 2

    11. Which of these transitions correspond to absorption and which to emission of radiation (or energy in general)? Illustrate each transition on the provided energy level diagram.

    a) n = 2 to n = 4

    b) n = 3 to n = 1

    c) n = 5 to n = 2

    d) n = 3 to n = 4

    (note that as n increases, the levels get closer and closer together)

    e) Of the transitions listed above, which corresponds to emission of radiation with the longest wavelength? Explain. You should not need to use your calculator to answer this! f) Of the transitions listed above, which corresponds to absorption of radiation with the highest frequency? Explain. You should not need to use your calculator to answer this!

    E

    n=1

    n=2

    n=3

    n=4 n=5

  • Chem 1A Dr. White Fall 2013 5 12. Calculate the wavelength (in nm) of the photon emitted when a hydrogen atom undergoes a transition from n = 5 to n = 2. Is this visible light? 13. An electron in a hydrogen atom undergoes a transition from the n = 3 level to the n = 6 level. To

    accomplish this, energy, in the form of light, must be absorbed by the hydrogen atom. a) Calculate the energy of the light (in kJ/photon) associated with this transition. Watch the sign of

    your answer! b) In order to move to the n = 5 level, would this same electron need to absorb more or less

    energy? Explain.

    14. An electron in a hydrogen atom in the n = 5 level emits a photon with wavelength 1281 nm. a) To what energy level does this electron move? b) In order to move to the n = 1 level, will this electron emit a photon with longer or shorter wavelength

    than 1281 nm? Explain. Again, you should not need to use your calculator here.

    15.