CHEM
Ex_1D_KEY.pdf

# A k and i b i and no 3 c k and no 3 d k and pb 2 e pb

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(A) K + and I (B) I and NO 3 (C) K + and NO 3 (D) K + and Pb 2+ (E) Pb 2+ and I = Pb 2+ = NO 3 = K + = I (A) (B) (C) (D) (E)

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D6 © 2018 L.S. Brown (6 pts) 15. Aluminum (Al, 2.70 g/cm 3 ) and strontium (Sr, 2.64 g/cm 3 ) have nearly the same density. Suppose you had 2 cubes, one made of pure aluminum and the other made of pure strontium, with each cube containing 1 mole of its element. Which cube would be smaller, and what would the edge length of the smaller cube be? (A) Al, 2.15 cm (B) Al, 3.16 cm (C) Sr, 5.76 cm (D) Sr, 3.21 cm (E) Both cubes would be the same size, 1.39 cm Molar masses are 26.98 g/mol for Al and 87.62 g/mol for Sr. Because the aluminum is so much lighter, it will be the small cube. Use density to get volume, and then cube root to get edge length of cube. ࠵?࠵?. ࠵?࠵? ࠵? ࠵?. ࠵?࠵? ࠵? ࠵?࠵? –࠵? = ࠵?. ࠵?࠵? ࠵?࠵? ࠵? ࠵?࠵?࠵? (࠵?. ࠵?࠵?) ࠵? ࠵? = ࠵?. ࠵?࠵? ࠵?࠵? (6 pts) 16. On February 2 the market price for palladium metal was \$1040 per troy ounce. How many palladium (Pd, Z = 46) atoms could you buy for \$1.00? (1 troy ounce = 31.103 g) (A) 1.92 ´ 10 24 (B) 1.69 ´ 10 20 (C) 9.79 ´ 10 19 (D) 3.57 ´ 10 18 (E) 1.75 ´ 10 17 \$࠵? × ࠵? ࠵?࠵? ࠵? \$࠵?࠵?࠵?࠵? × ࠵?࠵?. ࠵?࠵?࠵? ࠵? ࠵? ࠵?࠵? ࠵? × ࠵? ࠵?࠵?࠵? ࠵?࠵?࠵?. ࠵?࠵? ࠵? ࠵?࠵? × ࠵?. ࠵?࠵?࠵? × ࠵?࠵? ࠵?࠵? ࠵?࠵?࠵?࠵?࠵? ࠵? ࠵?࠵?࠵? = ࠵?. ࠵?࠵? × ࠵?࠵? ࠵?࠵? ࠵?࠵?࠵?࠵?࠵?
NAME:______________________________________ © 2018 L.S. Brown D7 (10 pts) 17. The pink color of salmon is largely due to the presence of astaxanthin. Elemental analysis shows that astaxanthin contains 80.50% carbon, 8.78% hydrogen, and 10.72% oxygen by mass. Another test shows that the molar mass of the compound is between 500 and 650 g/mol. Find the molecular formula for astaxanthin. We can use the percentages to find the empirical formula, then it should turn out that only one multiple of it will be in the given mass range. Start by taking a 100 g sample and converting the masses to moles, then divide by the smallest number of moles: 80.50 g C 12.01 g/mol = 6.703 mol C ÷ 0.670 = 10.00 8.78 g H 1.008 g/mol = 8.710 mol H ÷ 0.670 = 13.00 10.72 g O 16.00 g/mol = 0.670 mol O ÷ 0.670 = 1 So our empirical formula is C 10 H 13 O That would have a molar mass of ~149 g/mol. So the only multiple that will fall between 500 and 650 is to multiply that by 4, giving us the molecular formula of: C 40 H 52 O 4

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