Q: What is the formula for calculating the weighted average atomic mass of an element with multiple isotopes?

$$M_{av} = \sum \left( \frac{\%\ \text{abundance of isotope}}{100\%} \times M_{\text{isotope}} \right)$$

Question 1

Which scientist is credited with the discovery of the law of conservation of mass, and what does this law state?

Accepted Answer

Antoine Lavoisier; mass is neither created nor destroyed in a chemical reaction.

Question 2

According to Dalton's atomic theory, which statement is now known to be incorrect?

Accepted Answer

Atoms of a given element are identical in mass and all other properties.

Question 3

What is the main difference between isotopes of the same element?

Accepted Answer

They have different numbers of neutrons.

Question 4

Which subatomic particle is responsible for the identity of an element?

Accepted Answer

Proton

Question 5

A sample of silicon contains three isotopes: $$^{28}Si (92.23$$%, 27.9769 u), $$^{29}Si (4.67$$%, 28.9765 u), and $$^{30}Si (3.10$$%, 29.9738 u). Calculate the average atomic mass of silicon.

Accepted Answer

$$28.09\ 	ext{u}$$

Question 6

Which technique is commonly used to determine the relative abundance of isotopes in a sample?

Accepted Answer

Mass spectrometry

Question 7

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number: 17, Mass number: 35

Question 8

Which real-world application uses isotope ratios to determine the year of birth from tooth enamel?

Accepted Answer

Forensic analysis using $$^{14}C$$ levels

Question 9

What is the formula for calculating the weighted average atomic mass of an element with multiple isotopes?

Accepted Answer

$$M_{av} = \sum \left( \frac{\%\ 	ext{abundance of isotope}}{100\%} 	imes M_{	ext{isotope}} ight)$$

Question 10

Gallium has two naturally occurring isotopes: $$^{69}Ga (68.926 u) $$and $$^{71}Ga (70.925 u). $$The average atomic mass is 69.723 u. Which isotope is more abundant?

Accepted Answer

$$^{69}Ga$$

Question 11

Which statement best describes the nucleus of an atom?

Accepted Answer

It contains most of the atom's mass and is positively charged.

Question 12

Which of the following is a correct definition of a nucleon?

Accepted Answer

A particle found in the nucleus, either a proton or a neutron.

Question 13

If the number of protons in an atom changes, what is the result?

Accepted Answer

The atom becomes a different element.

Question 14

Which law states that a chemical compound always contains the same proportion of elements by mass?

Accepted Answer

Law of constant composition (definite proportions)

Question 15

Which of the following best explains why most of an atom is considered empty space?

Accepted Answer

The nucleus occupies a tiny fraction of the atom's volume.

Question 16

A forensic scientist uses mass spectrometry to analyze a tooth sample. What property of isotopes allows this technique to distinguish between them?

Accepted Answer

Different masses

Question 17

Which of the following elements has only one naturally occurring isotope?

Accepted Answer

Sodium

Question 18

What is the charge of an atom with 12 protons and 10 electrons?

Accepted Answer

+2

Question 19

Which historical experiment provided evidence for the existence of a small, dense nucleus in the atom?

Accepted Answer

Rutherford's gold foil experiment

Question 20

Which of the following best describes the relationship between atomic number ($$Z) $$and mass number ($$A$$)?

Accepted Answer

$$A = Z + 	ext{number of neutrons}$$

Atomic Structure, Isotopes, and Atomic Mass: Foundations of Modern Chemistry

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