Textbook Question
(a) What are the C—C—C bond angles in diamond?
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Ch.12 - Solids and Modern Materials
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement140
- Ch.2 - Atoms, Molecules, and Ions192
- Ch.3 - Chemical Reactions and Reaction Stoichiometry172
- Ch.4 - Reactions in Aqueous Solution156
- Ch.5 - Thermochemistry151
- Ch.6 - Electronic Structure of Atoms137
- Ch.7 - Periodic Properties of the Elements127
- Ch.8 - Basic Concepts of Chemical Bonding143
- Ch.9 - Molecular Geometry and Bonding Theories167
- Ch.10 - Gases147
- Ch.11 - Liquids and Intermolecular Forces97
- Ch.12 - Solids and Modern Materials129
- Ch.13 - Properties of Solutions126
- Ch.14 - Chemical Kinetics175
- Ch.15 - Chemical Equilibrium107
- Ch.16 - Acid-Base Equilibria127
- Ch.17 - Additional Aspects of Aqueous Equilibria133
- Ch.18 - Chemistry of the Environment88
- Ch.19 - Chemical Thermodynamics140
- Ch.20 - Electrochemistry137
- Ch.21 - Nuclear Chemistry99
- Ch.22 - Chemistry of the Nonmetals66
- Ch.23 - Transition Metals and Coordination Chemistry69
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry11
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 12, Problem 124b
The karat scale used to describe gold alloys is based on mass percentages. (b) If an alloy is formed that is 50 mol% copper and 50 mol% gold, what is the karat number of the alloy? What is the color of this alloy?
Verified step by step guidance1
Determine the molar masses of copper (Cu) and gold (Au).
Calculate the mass percentages of copper and gold in the alloy using their molar masses and the given molar percentages (50 mol% Cu and 50 mol% Au).
Locate the mass percentages of copper and gold on the triangular diagram provided.
Identify the karat number of the alloy by comparing the mass percentage of gold to the karat scale on the diagram.
Determine the color of the alloy by finding the corresponding region on the diagram based on the mass percentages of copper and gold.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Karat Scale
The karat scale is a measure of the purity of gold alloys, where 24 karats represents pure gold. The karat number is calculated based on the mass percentage of gold in the alloy. For example, an 18-karat gold alloy contains 75% gold and 25% other metals, while a 14-karat alloy contains 58.3% gold. Understanding this scale is essential for determining the quality and value of gold jewelry.
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Mole Fraction and Mass Percentage
Mole fraction is the ratio of the number of moles of a component to the total number of moles in a mixture, while mass percentage is the mass of a component divided by the total mass of the mixture, multiplied by 100. In the context of the question, the alloy is composed of 50 mol% copper and 50 mol% gold, which can be converted to mass percentages to determine the karat number. This conversion is crucial for accurate calculations.
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Color of Gold Alloys
The color of gold alloys is influenced by the types and proportions of metals mixed with gold. Copper imparts a reddish hue, while silver contributes a yellowish tint. The triangular diagram illustrates how varying the mass percentages of gold, copper, and silver affects the resulting color of the alloy. For the given alloy of 50% gold and 50% copper, the color is expected to be reddish, indicating a significant copper content.
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Related Practice
Textbook Question
(b) X-ray diffraction studies of buckminsterfullerene show that it has a face-centered cubic lattice of C60 molecules. The length of an edge of the unit cell is 14.2 Å. Calculate the density of buckminsterfullerene.
Textbook Question
The karat scale used to describe gold alloys is based on mass percentages. (a) If an alloy is formed that is 50 mol% silver and 50 mol% gold, what is the karat number of the alloy? Use Figure 12.18 to estimate the color of this alloy.
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Textbook Question
(b) What are they in graphite (in one sheet)?