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Ch.3 - Chemical Reactions and Reaction Stoichiometry
Chapter 3, Problem 91e

Very small semiconductor crystals, composed of approximately 1000 to 10,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors, depending on dot size. The density of CdSe is 5.82 g/cm3. (e) If you wanted to make one 6.5-nm dot from multiple 2.5-nm dots, how many 2.5-nm dots would you need, and how many CdSe formula units would be left over, if any?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Quantum Dots

Quantum dots are nanoscale semiconductor particles that have unique optical and electronic properties due to their size. Their ability to emit light in various colors is size-dependent, meaning that smaller dots emit different wavelengths than larger ones. This property makes them valuable in applications like displays and sensors.
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Volume and Density Calculations

To determine how many smaller quantum dots are needed to create a larger one, one must understand the relationship between volume and density. The volume of a dot can be calculated using its radius, and the density allows for the conversion between mass and volume. This is essential for calculating how many smaller dots fit into the volume of the larger dot.
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Molar Mass and Formula Units

The molar mass of a substance, such as CdSe, is crucial for converting between grams and moles, which helps in determining the number of formula units in a given mass. Understanding how to calculate the number of formula units from the mass of the material allows for accurate assessments of leftover material after forming larger structures from smaller ones.
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Related Practice
Textbook Question
Calcium is an essential nutrient in our body. It is important for bone health. Four common calcium-containing supplements are calcium carbonate (CaCO3), calcium citrate (Ca3C12H10O14), calcium gluconate (CaC12H22O14), and calcium lactate (CaC6H10O6). Rank these calcium supplements in terms of the mass percentage of calcium they contain.
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Textbook Question

Very small semiconductor crystals, composed of approximately 1000 to 10,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors, depending on dot size. The density of CdSe is 5.82 g/cm3. (a) What is the mass of one 2.5-nm CdSe quantum dot?

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Textbook Question

Very small semiconductor crystals, composed of approximately 1000 to 10,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors, depending on dot size. The density of CdSe is 5.82 g/cm3. (c) What is the mass of one 6.5-nm CdSe quantum dot?

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Textbook Question

(b) Hemoglobin, the oxygen-carrying protein in red blood cells, has four iron atoms per molecule and contains 0.340% iron by mass. Calculate the molar mass of hemoglobin.

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Textbook Question
Cinnamaldehyde is a compound that is responsible for the characteristic aroma of cinnamon. It contains 81.79% C, 6.10% H, and the remaining is oxygen. Its molar mass is 132 g/mol. Determine its molecular formula.
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Textbook Question
The fluoride ion reacts with water to produce HF. (a) Write out the chemical equation for this reaction.
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