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Midterm Review Day 1: Units 1 – 3 Review Stations – ANSWER KEY Station #1: Measurement & Dimensional Analysis 1. The most common unit used for mass in the chemistry laboratory is grams. This unit is commonly abbreviated as the letter g. 2. Convert 85.3 grams (g) to kilograms (kg). 0.0853 kg 3. Convert 120.8 grams (g) to ounces (oz.). 4.261 oz 4. The most common unit used for volume in the chemistry laboratory is liters. This unit is commonly abbreviated as the letter L. 5. Convert 784 liters (L) to milliliters (mL). 784,000 mL 6. The most common unit used for length in the chemistry laboratory is meters. This unit is commonly abbreviated as the letter m 7. Convert 13.4 centimeters (cm) to nanometers (nm). 134,000,000 nm Station #2: Scientific Notation & Significant Figures 1. Convert 987,600 to scientific notation. 9.876 x 105 2. Convert 5.688 x 10-4 to standard form. 0.0005688 3. Convert 0.000360 to scientific notation. 3.60 x 10-4 4. Determine the number of significant figures in each example 3030 0.007080 10.00 320. 8.6703 3 4 4 3 5 5. Solve each example + round to the correct number of significant figures 43.2 + 18.01 – 6.035 = 55.175 55.2 160 ÷ 10.5 = 15.238095 15 86.2 x 0.032 = 2.7584 2.8 17.3 – 0.005 + 0.10048 – 11 = 6.39548 6 178.1 ÷ 8.003 = 22.254154 22.25 36.2 ÷ 5 x 4.3 + 2.01 = 33.142 30 5. Which measurement is reported to a greater degree of accuracy: 0.009 cm or 0.00900 cm? 6. Calculate the percent error for a density that was measured by a student to be 9.80 g/mL, if the accepted value is 10.00 g/mL. (10.00 – 9.80) x 100 = 2.00% 10.00 Station #3: History of the Atom 1. What is the difference between Democritus’ and Dalton’s Model of the Atom? Very similar – both thought that atoms made up everything and were very small. Democritus named them, atomos, and Dalton said they were indivisible. 2. How did Rutherford build on Thomson’s discovery? Describe each of their experiments and what the outcomes were. Thomson used the cathode ray to determine that there was substructure to an atom (positive + negative charge) and described it as “plum pudding.” Rutherford shot alpha particles (positive charges) at a piece of gold foil and discovered the nucleus (where all the mass is contained) and that electrons were around it outside (all the space). 3. What are the similarities between the Bohr model and the electron cloud model? What are the differences? Very similar – both say the nucleus has all the mass (made of protons and neutrons) and both say electrons orbit the nucleus. Bohr said in a circle (planetary model) and the electron cloud model says that the orbits are not all circular in shape. 4. Who is credited with discovering the nucleus? Why? Rutherford. When he shot the alpha particles at the piece of foil they bounced back only in the center (the nucleus) where it was a dense concentration of protons. Station #4 – The Atom Complete the following table. Element Symbol Atomic # Atomic Mass # protons # neutrons # electrons Cadmium Cd 48 112 48 64 48 Praseodymium Pr 59 140 59 81 59 Lead Pb 82 207 82 125 82 Tungsten W 74 184 74 110 74 Nuclear Symbol 112 Cd 48 140 Pr 59 207 Pb 82 184 W 74 Station #5 – The Ion Complete the following table. Element Ion Symbol Atomic # Atomic Mass # protons # neutrons # electrons Cobalt Co2+ 27 59 27 32 25 Aluminum Al3+ 13 27 13 14 10 Palladium Pb2+ 46 106 46 60 44 Iodine (-1) I- 53 127 53 74 54 Nuclear Symbol (include charge) 59 Co2+ 27 27 3+ Al 13 106 Pb2+ 46 127 I 53 Station #6 – The Isotope Complete the following table. Element Hyphen Notation Atomic # Atomic Mass # protons # neutrons # electrons Vanadium Vanadium-52 23 52 23 29 23 Barium Barium-139 56 139 56 83 56 Lead Lead-209 82 209 82 127 82 Silver Silver-109 47 109 47 62 47 Nuclear Symbol 52 V 23 209 Pb 82 209 Pb 82 109 Ag 47 Station #7 – Weighted Average Atomic Mass Solve the following problems + round your answer to the correct number of significant figures. 1. What is the average atomic mass of silicon given the following abundance information on the isotopes of silicon? Mass number Si-28 Si-29 Si-30 1. 2. 3. 4. 2. What is the average atomic mass of hafnium given the following information about the number of atoms of its isotopes? Abundance Mass number # Atoms Hf-176 35 Hf-177 100 Hf-178 45 Hf-179 250 Hf-180 120 92.21 % 4.70 % 3.09 % Turn abundance percentages into decimals (to make all relative to 1) Multiple by mass Add up Sig Figs! 0.9291 (28) = 26.0148 0.0471 (29) = 1.3659 0.0309 (30) = 0.927 28.3077 28 amu 1. 2. 3. 4. Turn # atoms into decimals (to make all relative to 1) by dividing by total number of atoms. Multiple by mass Add up Sig Figs! 35 + 100 + 45 + 250 + 120 = 550 total atoms 35/550 = 0.06364 (176) = 11.201 100/500 = 0.18182 (177) = 32.182 45/550 = 0.081818 (178) = 14.564 250/550 = 0.45455 (179) = 81.364 120/550 = 0.21818 (180) = 39.273 178.584 179 amu