Question

There is a 10.0 grams necklace made of 18K gold. K, karat, is a measurement of the fineness (or purity) of gold by Jeweler and gold dealers. Compared with 24K (pure gold), 18K means that the mass percent of gold is = 0.75 (or 75 wt%, we treat it as an exact number here). In another word, that necklace contain 75% gold by mass. If the international gold price today is $1323 (US) per troy ounce, and one troy ounce equals 31.103 grams, solve the following two questions: (a) How many gold atoms are contained in this necklace?

Answer 1

a) in 10.0 grams necklace, 75% of weight is of pure gold. Gold weight = 10.9 x 250 = 7.59. molar mass of gold = 196.96657 g/mol = 6.022 x 18²3 gold atoms 196.96657 grams = 6.022 x 103 atoms 7.59 = 7.5x6.022 X 1023 196.96657 2.2934 10 atoms Answer: 2.293 x 103 gold atoms will be present in 7.5g of pure gold or 10.0g of necklace 22 Lund

b) i troy ounce = 31.103 grams = $1323 10. 7.5g of pure gold = 7.5g * $1323 - 31.1039 = 319 Answer cost = $319. c) volume / will be lower than 75% since density & 1 volume (more density, less volume and vice-versa)