AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4

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AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4 Question: What is the formula for the compound composed of 71.62% gold, 13.10% carbon, and 15.28% nitrogen? AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4 In 100 g of the compound, there are 71.62 grams of gold, 13.10 grams of carbon, and 15.28 grams of nitrogen. Need to convert these masses to moles  divide by atomic mass Script: CLICK Question: What is the formula for the compound composed of 71.62% gold, 13.10% carbon, and 15.28% nitrogen? Is it A, AuCN; B, Au(CN)2; C, Au(CN)3; or D, Au(CN)4? In 100 grams of the compound, there are 71.62 grams of gold, 13.10 grams of carbon, and 15.28 grams of nitrogen. The formula gives us the ratio of the number of atoms. It also gives us the ratio of the number of moles. To figure out the formula, we need to convert these masses to moles. To convert mass to moles, we divide by the atomic mass.

Script: From the periodic table we get atomic masses of CLICK 197.0 grams per mole for gold, 12.01 grams per mole for carbon, and 14.01 grams per mole for nitrogen.

Empirical formula: AuC3N3 1 mol Au 197.0 g Au = 0.3636 mol Au Moles Au = 71.62 g Au x 1 mol C 12.01 g C Moles C = 13.10 g C x = 1.091 mol C 1 mol N 14.01 g N Moles N = 15.28 g N x = 1.091 mol N Script: So to figure out the number of moles of gold, CLICK we multiply 71.62 grams of gold by one mole of gold over 197.0 grams of gold. We have a number with four significant figures divided by another number with four significant figures so our answer should have four significant figures. Grams of gold cancel, leaving us with moles of gold for our units. This gives us 0.3636 moles of gold. Next we do carbon. Multiplying 13.10 grams of carbon by 1 mole of carbon over 12.01 grams of carbon gives us 1.091 moles of carbon. For nitrogen, multiplying 15.28 grams of nitrogen by 1 mole of nitrogen over 14.01 grams of nitrogen gives us 1.091 moles of nitrogen. We now need to convert these numbers of moles to the simplest whole number ratio. To do that we divide each number of moles by the smallest number of moles. The smallest number is 0.3636, the number of moles of gold. Dividing 0.3636 by 0.3636 gives us 1, while dividing 1.091 by 0.3636 gives us 3. So for each mole of gold we have 3 moles each of carbon and nitrogen, giving us an empirical formula of AuC3N3. Au 0.3636 0.3636 C 1.091 0.3636 N 1.091 0.3636 = 1 = 3 = 3 Empirical formula: AuC3N3

A. AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4 What is the formula for the compound composed of 71.62% gold, 13.10% carbon, and 15.28% nitrogen? A. AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4 Script: There is an ion with equal amounts of carbon and nitrogen, CN-, the cyanide ion, so we can change this formula to Au(CN)3. So the correct answer is C. CLICK

Video ID: 4-7-JJW-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Jeremy Wessel Narrator: ? Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08