Q: Calculate the number of moles of carbon in $$0.0265\ \mathrm{g} of $$pencil lead (assume pure carbon, $$12.01\ \mathrm{g/mol}).$$

$$2.21 \times 10$$^{-3}$$\ \mathrm{mol}$$

Q: A penny has a mass of $$3.10\ \mathrm{g}$$ and is made of pure copper ($$63.55\ \mathrm{g/mol}). $$How many copper atoms are in the penny? ($$1\ \mathrm{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$2.94 \times 10$$^{22}$$ atoms

Question 1

Which of the following best describes the Law of Conservation of Mass as demonstrated by Lavoisier's experiments?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

A sample of sodium chloride (NaCl) is analyzed and found to contain 39.3 g of Na and 60.7 g of Cl. If a second sample contains 78.6 g of Na, how many grams of Cl should it contain according to the Law of Definite Proportions?

Accepted Answer

$$121.4\ \mathrm{g}$$

Question 3

Which statement is NOT a postulate of Dalton’s Atomic Theory?

Accepted Answer

Atoms of the same element can have different masses.

Question 4

Which experiment provided evidence for the existence of the electron as a negatively charged particle?

Accepted Answer

Thomson's cathode ray tube experiment

Question 5

Millikan’s oil drop experiment was crucial in determining which property of the electron?

Accepted Answer

The charge of the electron

Question 6

Which of the following statements about Rutherford’s gold foil experiment is correct?

Accepted Answer

Most alpha particles passed straight through the foil, indicating that atoms are mostly empty space.

Question 7

An atom of $$^{23}\mathrm{Na}^+$$ has how many protons, neutrons, and electrons?

Accepted Answer

11 protons, 12 neutrons, 10 electrons

Question 8

Which of the following best explains why isotopes of the same element have different mass numbers?

Accepted Answer

They have different numbers of neutrons.

Question 9

Calculate the number of moles of carbon in $$0.0265\ \mathrm{g} of $$pencil lead (assume pure carbon, $$12.01\ \mathrm{g/mol}).$$

Accepted Answer

$$2.21 	imes 10$$^{-3}$$\ \mathrm{mol}$$

Question 10

A penny has a mass of $$3.10\ \mathrm{g}$$ and is made of pure copper ($$63.55\ \mathrm{g/mol}). $$How many copper atoms are in the penny? ($$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$2.94 	imes 10$$^{22}$$ atoms

Question 11

Which sample contains the greatest number of atoms: $$1\ \mathrm{g} of $$copper ($$63.55\ \mathrm{g/mol}$$), $$1\ \mathrm{g} of $$carbon ($$12.01\ \mathrm{g/mol}$$), or $$1\ \mathrm{g} of $$uranium ($$238.03\ \mathrm{g/mol}$$)?

Accepted Answer

$$1\ \mathrm{g} of $$carbon

Question 12

Which of the following is the correct definition of atomic number ($$Z$$)?

Accepted Answer

The number of protons in the nucleus of an atom

Question 13

A neutral atom of $$^{13}\mathrm{C}$$ contains how many protons, neutrons, and electrons?

Accepted Answer

6 protons, 7 neutrons, 6 electrons

Question 14

Which of the following best describes the Law of Multiple Proportions?

Accepted Answer

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

Question 15

Which of the following statements about the nucleus of an atom is correct?

Accepted Answer

The nucleus contains nearly all the mass of the atom and is positively charged.

Question 16

Which of the following is the correct value for Avogadro’s number?

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 17

Which of the following best explains why atoms are electrically neutral?

Accepted Answer

The number of protons equals the number of electrons.

Question 18

A neon atom has three naturally occurring isotopes: $$^{20}\mathrm{Ne} (90.48$$%, 19.9924 amu), $$^{21}\mathrm{Ne} (0.27$$%, 20.9940 amu), and $$^{22}\mathrm{Ne} (9.25$$%, 21.9914 amu). What is the average atomic mass of neon?

Accepted Answer

$$20.18\ \mathrm{amu}$$

Question 19

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons and is positively charged.

Question 20

Which of the following is the correct conversion factor to use when converting from grams of an element to number of atoms?

Accepted Answer

$$\frac{1\ \mathrm{mol}}{	ext{molar mass in g}} 	imes \frac{6.022 	imes 10$$^{23}$$\ 	ext{atoms}}{1\ \mathrm{mol}}$$

Atoms and the Foundations of Modern Chemistry

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