Ex_1C_KEY.pdf

# Suppose you had 2 cubes one made of pure aluminum and

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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 larger, and what would the edge length of the larger cube be? (A) Al, 2.15 cm (B) Sr, 3.21 cm (C) Al, 3.16 cm (D) Sr, 5.76 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 strontium is so much heavier, it will be the big 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 rhodium metal was \$1860 per troy ounce. How many rhodium (Rh, Z = 45) atoms could you buy for \$1.00? (1 troy ounce = 31.103 g) (A) 9.79 ´ 10 19 (B) 1.69 ´ 10 20 (C) 1.04 ´ 10 24 (D) 3.15 ´ 10 18 (E) 1.02 ´ 10 17 \$࠵? × ࠵? ࠵?࠵? ࠵? \$࠵?࠵?࠵?࠵? × ࠵?࠵?. ࠵?࠵?࠵? ࠵? ࠵? ࠵?࠵? ࠵? × ࠵? ࠵?࠵?࠵? ࠵?࠵?࠵?. ࠵?࠵? ࠵? ࠵?࠵? × ࠵?. ࠵?࠵?࠵? × ࠵?࠵? ࠵?࠵? ࠵?࠵?࠵?࠵?࠵? ࠵? ࠵?࠵?࠵? = ࠵?. ࠵?࠵? × ࠵?࠵? ࠵?࠵? ࠵?࠵?࠵?࠵?࠵?

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NAME:______________________________________ © 2018 L.S. Brown C7 (10 pts) 17. The yellow color of corn, mangos, and egg yolks is due in part to the presence of zeaxanthin. Elemental analysis shows that zeaxanthin contains 84.45% carbon, 9.92% hydrogen, and 5.63% oxygen by mass. Another test shows that the molar mass of the compound is between 400 and 600 g/mol. Find the molecular formula for zeaxanthin. 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: 84.45 g C 12.01 g/mol = 7.032 mol C ÷ 0.352 = 19.98 ≈ 20 9.92 g H 1.008 g/mol = 9.841 mol H ÷ 0.352 = 27.97 ≈ 28 5.63 g O 16.00 g/mol = 0.352 mol O ÷ 0.352 = 1 So our empirical formula is C 20 H 28 O That would have a molar mass of ~284 g/mol. So the only multiple that will fall between 400 and 600 is to double that, giving us the molecular formula of: C 40 H 56 O 2
C8 © 2018 L.S. Brown (10 pts) 18. Calcium carbonate (limestone, CaCO 3 ) dissolves in hydrochloric acid, producing water and carbon dioxide as shown in the following equation. Calcium chloride is a soluble ionic compound, so it dissociates to give calcium ions and chloride ions. Suppose 10.50 g of solid

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