Question 1

Which experiment or law first provided strong evidence that mass is conserved during chemical reactions, and who is credited with its discovery?

Accepted Answer

The law of conservation of mass by Antoine Lavoisier

Question 2

A forensic scientist is analyzing a sample of tooth enamel to determine the age of a skeleton. Which property of atoms is most directly useful for this analysis?

Accepted Answer

The isotopic ratio of carbon-14 to carbon-12

Question 3

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 4

A sample of chlorine contains 75.8% 35Cl (mass = 34.97 u) and 24.2% 37Cl (mass = 36.97 u). What is the average atomic mass of chlorine?

Accepted Answer

35.45 u

Question 5

Which of the following best explains why the atomic mass of an element on the periodic table is rarely a whole number?

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 6

Which of the following changes would result in a different element?

Accepted Answer

Changing the number of protons in the nucleus

Question 7

A neutral atom of magnesium has an atomic number of 12 and a mass number of 24. How many neutrons does it contain?

Accepted Answer

12

Question 8

Which of the following best describes the structure of the atom according to modern understanding?

Accepted Answer

Most of the atom's mass is in a tiny, dense nucleus, with electrons moving in mostly empty space around it.

Question 9

Which of the following statements about mass spectrometry is correct?

Accepted Answer

It separates isotopes based on their mass and shows their relative abundances.

Question 10

A sample contains two isotopes of element X: 60% X-29 (mass = 29 u) and 40% X-30 (mass = 30 u). What is the average atomic mass of element X?

Accepted Answer

29.4 u

Question 11

Which of the following is a direct application of the law of definite proportions?

Accepted Answer

A chemist finds that water from different sources always contains 11% hydrogen and 89% oxygen by mass.

Question 12

Which of the following best describes Dalton’s contribution to atomic theory?

Accepted Answer

He proposed that all matter is made of indivisible atoms that combine in whole-number ratios.

Question 13

A neutral 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 14

Which of the following real-world scenarios best illustrates the use of isotopic abundances?

Accepted Answer

Dating ancient artifacts using carbon-14 levels

Question 15

If an atom has a charge of +2, 20 protons, and 18 electrons, what is its atomic number?

Accepted Answer

20

Question 16

Which statement about subatomic particles is correct?

Accepted Answer

Protons and neutrons have nearly the same mass.

Question 17

A scientist finds a new element with two isotopes: 10% with mass 100 u and 90% with mass 102 u. What is the average atomic mass?

Accepted Answer

101.8 u

Question 18

Which of the following would NOT change the identity of an atom?

Accepted Answer

Removing a neutron from the nucleus

Question 19

Which of the following best explains why most of the mass of an atom is concentrated in the nucleus?

Accepted Answer

The nucleus contains protons and neutrons, which are much more massive than electrons.

Question 20

Which of the following is a correct application of the law of conservation of mass in a real-world chemical reaction?

Accepted Answer

The total mass of reactants and products in a sealed reaction vessel remains constant.

Atomic Structure and Isotopes: Foundations and Applications

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