Ch.2 - Atoms & Elements

Tro - Chemistry: A Molecular Approach 4th Edition

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Tro 4th Edition

Ch.2 - Atoms & Elements

Problem 102

Chapter 2, Problem 102

Use the mass spectrum of mercury to estimate the atomic mass of mercury. Estimate the masses and percent intensity values from the graph to three significant figures.

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Identify the isotopes of mercury present in the mass spectrum and note their respective mass numbers and percent intensities.

Convert the percent intensities into fractional abundances by dividing each percent intensity by 100.

Multiply each isotope's mass number by its fractional abundance to find the contribution of each isotope to the atomic mass.

Sum the contributions from all isotopes to estimate the atomic mass of mercury.

Ensure that the final estimated atomic mass is reported to three significant figures, as required by the problem.

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Key Concepts

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

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio (m/z) of ions. It provides information about the different isotopes of an element and their relative abundances. In the context of mercury, the mass spectrum will show peaks corresponding to the various isotopes, allowing for the estimation of the average atomic mass based on their intensities.

Atomic Mass

Atomic mass is the weighted average mass of an element's isotopes, measured in atomic mass units (amu). It takes into account both the mass of each isotope and its relative abundance in nature. To estimate the atomic mass of mercury from its mass spectrum, one must calculate the average based on the isotopes' masses and their percent intensity values.

Percent Intensity

Percent intensity in a mass spectrum indicates the relative abundance of each isotope compared to the most abundant isotope, expressed as a percentage. This value is crucial for calculating the weighted average atomic mass, as it reflects how much each isotope contributes to the overall mass of the element. Accurate estimation of these values is essential for deriving the atomic mass of mercury.

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Textbook Question

Naturally occurring iodine has an atomic mass of 126.9045 amu. A 12.3849 g sample of iodine is accidentally contaminated with an additional 1.00070 g of ¹²⁹I, a synthetic radioisotope of iodine used in the treatment of certain diseases of the thyroid gland. The mass of ¹²⁹I is 128.9050 amu. Find the apparent 'atomic mass' of the contaminated iodine.

An a particle, 4He2 + , has a mass of 4.00151 amu. Find the value of its charge-to-mass ratio in C/kg.

Use the mass spectrum of lead to estimate the atomic mass of lead. Estimate the mass and percent intensity values from the graph to three significant figures.

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Textbook Question

Nuclei with the same number of neutrons but different mass numbers are called isotones. Write the symbols of four isotones of ²³⁶Th.

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