Ch.2 - Atoms, Molecules, and Ions

Problem 90b

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Chapter 2, Problem 90b

(b) How many molecules of C13H18O2 are in this tablet?

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Key Concepts

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

Molecular Formula

The molecular formula of a compound indicates the number and type of atoms present in a molecule. For C13H18O2, it shows that each molecule contains 13 carbon atoms, 18 hydrogen atoms, and 2 oxygen atoms. Understanding the molecular formula is essential for calculating the number of molecules in a given mass of the substance.

Avogadro's Number

Avogadro's number, approximately 6.022 x 10^23, is the number of atoms, ions, or molecules in one mole of a substance. This constant allows chemists to convert between the number of moles and the number of individual molecules, which is crucial for determining how many molecules are present in a specific quantity of a compound.

Molar Mass

The molar mass of a compound is the mass of one mole of that substance, typically expressed in grams per mole (g/mol). For C13H18O2, calculating the molar mass involves summing the atomic masses of all atoms in the molecular formula. This value is necessary for converting grams of the substance to moles, which can then be used to find the number of molecules.

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Molar Mass Concept

Related Practice

A cube of gold that is 1.00 cm on a side has a mass of 19.3 g. A single gold atom has a mass of 197.0 u. (a) How many gold atoms are in the cube?

1045

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Textbook Question

A cube of gold that is 1.00 cm on a side has a mass of 19.3 g. A single gold atom has a mass of 197.0 u. (b) From the information given, estimate the diameter in Å of a single gold atom.

912

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Textbook Question

The diameter of a rubidium atom is 495 pm We will consider two different ways of placing the atoms on a surface. In arrangement A, all the atoms are lined up with one another to form a square grid. Arrangement B is called a close-packed arrangement because the atoms sit in the 'depressions' formed by the previous row of atoms: (a) Using arrangement A, how many Rb atoms could be placed on a square surface that is 1.0 cm on a side?

488

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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. (b) CdSe quantum dots that are 2.5 nm in diameter emit blue light upon stimulation. Assuming that the dot is a perfect sphere and that the empty space in the dot can be neglected, calculate how many Cd atoms are in one quantum dot of this size.

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Textbook Question

(a) Assuming the dimensions of the nucleus and atom shown in Figure 2.10, what fraction of the volume of the atom is taken up by the nucleus?

384

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Textbook Question

(b) Using the mass of the proton from Table 2.1 and assuming its diameter is 1.0 * 10-15 m, calculate the density of a proton in g>cm3.

623

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