Question 1

Which of the following best describes the law of definite proportions?

Accepted Answer

A chemical compound always contains the same elements in the same proportion by mass, regardless of the source.

Question 2

A sample of calcium carbonate ($$\mathrm{$$CaCO_3$$}) is $$analyzed and found to contain 10.0 g of calcium, 3.0 g of carbon, and 12.0 g of oxygen. If a second sample of calcium carbonate is found to contain 20.0 g of calcium, how much oxygen should it contain according to the law of definite proportions?

Accepted Answer

$$24.0\ \mathrm{g}$$

Question 3

Which experiment provided the first direct evidence for the existence of electrons as subatomic particles?

Accepted Answer

The cathode ray tube experiment

Question 4

Which statement about isotopes is correct?

Accepted Answer

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

Question 5

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 6

Which of the following best explains why the mass of a helium atom is approximately four times that of a hydrogen atom, even though helium has only two protons?

Accepted Answer

Helium atoms contain two protons and two neutrons, while hydrogen atoms typically have only one proton and no neutrons.

Question 7

Which of the following statements is consistent with Dalton’s atomic theory as originally proposed?

Accepted Answer

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

Question 8

A sample contains $$51.84\% of$$ $$^{107}\mathrm{Ag} ($$atomic mass $$106.9051\ \mathrm{amu}) $$and $$48.16\% of$$ $$^{109}\mathrm{Ag} ($$atomic mass $$108.9048\ \mathrm{amu}). $$What is the average atomic mass of silver?

Accepted Answer

$$107.87\ \mathrm{amu}$$

Question 9

Which of the following ions is formed when a neutral atom of chlorine gains one electron?

Accepted Answer

$$\mathrm{Cl^-}$$

Question 10

Which of the following best describes the result of Rutherford’s gold foil experiment?

Accepted Answer

Most alpha particles passed through the foil, but a few were deflected at large angles, indicating a small, dense, positively charged nucleus.

Question 11

Which of the following is the correct relationship between the number of protons, electrons, and the charge of an ion?

Accepted Answer

Number of electrons = Number of protons for a neutral atom; for an ion, electrons are gained or lost according to the charge.

Question 12

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group (vertical column) have similar chemical properties.

Question 13

A sample of carbon dioxide ($$\mathrm{CO_2$}) $$contains $$12.0\ \mathrm{g} of $$carbon. How many grams of oxygen are present in the sample?

Accepted Answer

$$32.0\ \mathrm{g}$$

Question 14

Which of the following best describes Avogadro’s number?

Accepted Answer

The number of particles in one mole of a substance, $$6.022 	imes 10$$^{23}$$.

Question 15

Which of the following is the correct molar mass of copper if its atomic mass is $$63.55\ \mathrm{amu}$$?

Accepted Answer

$$63.55\ \mathrm{g/mol}$$

Question 16

A neutral atom of sodium ($$\mathrm{Na}) $$has an atomic number of $$11. If it $$loses one electron, what is the resulting ion and its charge?

Accepted Answer

$$\mathrm{Na^+}$$, with a charge of $$+1$$

Question 17

Which of the following best explains why the atomic mass of an element on the periodic table is not a whole number?

Accepted Answer

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

Question 18

Which of the following statements about ions is correct?

Accepted Answer

Cations are positively charged ions formed when atoms lose electrons.

Question 19

A sample of a compound contains $$2.00\ \mathrm{g} of $$hydrogen and $$16.00\ \mathrm{g} of $$oxygen. What is the percent by mass of hydrogen in the compound?

Accepted Answer

$$11.1\%$$

Atoms and Elements: Foundations of Atomic Theory and Structure

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