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

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Presentation on theme: "AuCN B. Au(CN)2 C. Au(CN)3 D. Au(CN)4"— Presentation transcript:

1 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 grams of gold, grams of carbon, and 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 grams of gold, grams of carbon, and 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.

2 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 grams per mole for nitrogen.

3 Empirical formula: AuC3N3
1 mol Au 197.0 g Au = mol Au Moles Au = 71.62 g Au x 1 mol C 12.01 g C Moles C = 13.10 g C x = mol C 1 mol N 14.01 g N Moles N = 15.28 g N x = 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 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 moles of gold. Next we do carbon. Multiplying grams of carbon by 1 mole of carbon over grams of carbon gives us moles of carbon. For nitrogen, multiplying grams of nitrogen by 1 mole of nitrogen over grams of nitrogen gives us 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 , the number of moles of gold. Dividing by gives us 1, while dividing by 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 C 0.3636 N 0.3636 = 1 = 3 = 3 Empirical formula: AuC3N3

4 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

5 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


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