CHEMISTRY 107 Section 501 Mini-Exam Version A September 7, 2018 Dr. Larry Brown

Size: px

Start display at page:

Download "CHEMISTRY 107 Section 501 Mini-Exam Version A September 7, 2018 Dr. Larry Brown"

Mildred McGee
5 years ago
Views:

1 NAME: (print) KEY UIN #: CHEMISTRY 107 Section 501 Mini-Exam Version A September 7, 2018 Dr. Larry Brown This is a 25-minute exam, and contains 12 multiple choice questions. Point values for the different questions are as indicated. There should be 6 numbered pages, including this one. Page 6 is blank and can be used for scratch work if needed. There is also a periodic table attached to the back of the exam; you may tear the periodic table page off, and you do not need to turn that page in. There is a grid on the back of the periodic table on which you can record your answers so that you have a copy that you can compare to the key once that is posted. All questions should be answered on the scantron provided to you. You may use a calculator for this exam, but you may NOT retrieve or use any alphanumeric information or algorithms that might be stored in your calculator s memory. Please PRINT your name and UIN number above, and SIGN the honor code statement below. Also, please put your name on every page of the exam, in case a page gets detached from the exam. Potentially Useful Information PHYSICAL CONSTANTS Avogadro s Number N A = mol 1 CONVERSION FACTORS 1 amu = g 1 kg = 1,000 g 1 L = 1,000 ml 1 L = gallon "On my honor, as an Aggie, I have neither given nor received unauthorized aid on this exam." SIGNATURE: PLEASE DO NOT OPEN YOUR EXAM UNTIL TOLD TO DO SO. Exam 2018 L.S. Brown A1

2 Imagine that we had a balance that could compare the masses of small numbers of atoms of different elements. The figures below show the results of 2 such hypothetical experiments. The letters beside each balance pan identify the elements being weighed. Use these pictures to answer Questions 1 3. (These are NOT actual elements! Your answer should be based ONLY on these pictures.) G C E F (3 pts) 1. Which element has the larger molar mass? (A) Element C (B) Element E (C) Neither (D) There is no way to tell (3 pts) 2. Which element has more atoms per gram? (A) Element F (B) Element G (C) Neither (D) There is no way to tell (3 pts) 3. Which element has more atoms per mole? (A) Element F (B) Element G (C) Neither (D) There is no way to tell (5 pts) 4. The compound shown below is furaneol, which is partially responsible for the scent of fresh strawberries. What is its molar mass, rounded to the nearest whole number? O Formula is C6H8O3 HO O (A) 142 g/mol (B) 100 g/mol (C) 127 g/mol (D) 141 g/mol (E) 128 g/mol (4 pts) 5. The molarity of a solution is defined as the number of of solute per of solution. (A) moles, liter (C) grams, liter (E) grams, mole (B) moles, kilogram (D) grams, kilogram A L.S. Brown

3 NAME: (3 pts) 6. Which contains the most atoms? (B) 1 mole of NO2 (3 pts) 7. Which contains the most oxygen atoms? (B) 1 mole of NO2 (3 pts) 8. Which contains the most molecules? (B) 1 moles of NO2 (6 pts) 9. A compound called acrylonitrile is the monomer for a range of polymers known as acrylics that are commonly used in carpets and clothing. Given that the molecule contains 67.90% carbon, 5.70% hydrogen, and 26.40% nitrogen, which is the correct empirical formula for acrylonitrile? (A) C5H5N (B) C6H6N2 (C) C3H3N (D) CH5N (E) C12HN5 Start with 100 g sample. Convert g of each element to moles, then divide by the smallest number of moles to get whole number ratio for coefficients g C = mol C = g/mol 5.70 g H = mol H = g/mol g N = mol N = g/mol So our empirical formula is C3H3N 2018 L.S. Brown A3

4 (5 pts) 10. What mass of solid Mg(NO3)2 should be dissolved to prepare ml of solution containing M Mg(NO3)2(aq)? (A) 26.3 g (B) 3.45 g (C) 108 g (D) 5.93 g (E) 33.6 g L mol 1 L g 1 mol = g (6 pts) 11. Seawater contains trace amounts of gold as aqueous Au + ions. The average gold content of the oceans has been estimated as g Au + per kg of seawater, and the density of seawater is about 1.03 g/ml. Although the concentration of gold is small, the oceans are large: the total volume of the world s oceans is about gallons. The price of gold is currently $1202 per troy ounce, and 1 troy ounce = g. Estimate the total dollar value of all of the gold dissolved in the oceans. (A) $ (B) $ (C) $ (D) $ (E) $ This is really just a lot of unit conversions gal 1 L 1000 ml g gal 1 L 1 ml 1 kg 1000 g g Au 1 kg 1 troy oz g $1202 = $ troy oz A L.S. Brown

5 NAME: (6 pts) 12. The element rubidium (Rb) has 2 stable isotopes, with the isotopic masses shown below. Isotope Mass 85 Rb Rb Given that the atomic weight of rubidium is g/mol, what is the isotopic abundance of the 87 Rb isotope? (A) 32.69% (B) 27.84% (C) 79.78% (D) 20.22% (E) 38.15% You had one like this in problem set #1. at wt = X 87 m 87 + (1 X 87 )m 85 = X 87 (m 87 m 85 ) + m 85 X 87 = at wt m 85 (m 87 m 85 ) = = L.S. Brown A5

CHEMISTRY 107 Section 501 Exam #1 Version A September 22, 2017 Dr. Larry Brown

NAME: (print) UIN #: CHEMISTRY 107 Section 501 Exam #1 Version A September 22, 2017 Dr. Larry Brown This is a 50-minute exam, and contains 14 multiple choice questions and 4 free response problems. Point