Question 1

Which of the following statements best explains the law of conservation of matter as supported by Dalton’s atomic theory?

Accepted Answer

Atoms are neither created nor destroyed during a chemical change; they are simply rearranged to form new substances.

Question 2

A sample of a compound contains 2.00 g of hydrogen and 16.00 g of oxygen. According to the law of definite proportions, what mass of oxygen would be present if the sample contained 4.00 g of hydrogen?

Accepted Answer

$$32.00\ \mathrm{g}$$

Question 3

Which experiment provided the first evidence that atoms contain smaller, negatively charged particles?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 4

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 5

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 6

A sample of boron contains 19.9% $$^{10}\mathrm{B} (10.0129 $$amu) and 80.1% $$^{11}\mathrm{B} (11.0093 $$amu). What is the average atomic mass of boron?

Accepted Answer

$$10.81\ \mathrm{amu}$$

Question 7

Which of the following is the correct symbol for an ion with 17 protons, 18 neutrons, and 18 electrons?

Accepted Answer

$$^{35}_{17}\mathrm{Cl}^{-}$$

Question 8

Which of the following best explains why most alpha particles passed straight through the gold foil in Rutherford’s experiment?

Accepted Answer

The gold atoms are mostly empty space.

Question 9

How many molecules are present in a 0.0400 g sample of saccharin ($$\mathrm{C}_7\mathrm{H}_5\mathrm{NO}_3\mathrm{S}$$, molar mass $$183.18\ \mathrm{g/mol}$$)?

Accepted Answer

$$1.31 	imes 10$$^{20}$$

Question 10

Which of the following is the empirical formula for acetic acid ($$\mathrm{C}_2\mathrm{H}_4\mathrm{O}_2$$)?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 11

A neutral atom of sodium ($$Z=11) $$loses one electron. What is the resulting charge and how many electrons does the ion have?

Accepted Answer

Charge: $$1+$$, Electrons: $$10$$

Question 12

Which of the following best describes the difference between a molecular formula and an empirical formula?

Accepted Answer

A molecular formula shows the actual number of atoms of each element in a molecule, while an empirical formula shows the simplest whole-number ratio of atoms.

Question 13

How many moles of potassium are present in a 4.70 g sample? (Molar mass of K = $$39.10\ \mathrm{g/mol})$$

Accepted Answer

$$0.120\ \mathrm{mol}$$

Question 14

Which of the following statements about subatomic particles is correct?

Accepted Answer

Protons and neutrons have nearly the same mass, while electrons are much lighter.

Question 15

A molecule of benzene has the molecular formula $$\mathrm{C}_6\mathrm{H}_6. $$What is its empirical formula?

Accepted Answer

$$\mathrm{CH}$$

Question 16

Which of the following best describes a structural isomer?

Accepted Answer

Compounds with the same molecular formula but different structural arrangements of atoms.

Question 17

If a sample contains $$9.2 	imes 10$$^{-4}$$ mol of argon, what is the mass of argon in the sample? (Molar mass of Ar = 39.95$$\ \mathrm{g/mol}$$)

Accepted Answer

$$0.0368\ \mathrm{g}$$

Question 18

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

Accepted Answer

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

Question 19

How many carbon atoms are present in a $$0.0400\ \mathrm{g}$$ sample of saccharin ($$\mathrm{C}_7\mathrm{H}_5\mathrm{NO}_3\mathrm{S}$$, molar mass $$183.18\ \mathrm{g/mol}$$)?

Accepted Answer

$$9.17 	imes 10$$^{20}$$

Atoms, Molecules, and Ions: Foundations of Atomic Theory and Chemical Formulas

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