Q: A silver ring contains $$2.80 \times 10$$^{22}$$ silver atoms. How many moles of silver does it contain? (1$$\ \text{mol} = 6.022 \times $$10^{23}$$ atoms)

$$4.65 \times 10$$^{-2}$$\ \text{mol}$$

Q: A naturally occurring element consists of two isotopes: 75.77% isotope A (mass 34.97 amu) and 24.23% isotope B (mass 36.97 amu). What is the atomic mass of the element?

$$0.7577 \times 34.97 + 0.2423 \times 36.97 = 35.45\ \text{amu}$$

Q: A cube of titanium contains $$2.86 \times 10$$^{22}$$ atoms. The density of titanium is 4.50$$\ \text{g/cm}^3$$. What is the edge length of the cube? (Molar mass of Ti = 47.87$$\ \text{g/mol}$$, 1$$\ \text{mol} = 6.022 \times $$10^{23}$$ atoms)

First, calculate moles: $$\frac{2.86 \times 10$$^{22}$$}{6.022 \times 10$$^{23}$$} = 0.0475\ \text{mol}$$; mass: $$0.0475\ \text{mol} \times 47.87\ \text{g/mol} = 2.27\ \text{g}$$; volume: $$\frac{2.27\ \text{g}}{4.50\ \text{g/cm}^3} = 0.504\ \text{cm}^3$$; edge length: $$\sqrt[3]{0.504} = 0.795\ \text{cm}$$

Question 1

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements in fixed, definite proportions.

Question 2

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen, and what law does this illustrate?

Accepted Answer

$$\frac{16.0\ g}{2.0\ g} = 8:1$$; this illustrates the law of definite proportions.

Question 3

Which statement about the scientific method is correct?

Accepted Answer

A scientific law summarizes past observations and predicts future ones.

Question 4

Which experiment led to the discovery of the electron and what property of the electron was first measured?

Accepted Answer

J.J. Thomson's cathode ray experiment; the charge-to-mass ratio of the electron.

Question 5

A neutral atom of chlorine has an atomic number $$Z = 17$$ and a mass number $$A = 35. $$How many protons, neutrons, and electrons does it have?

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 6

Which of the following is a homogeneous mixture?

Accepted Answer

Sweetened tea

Question 7

A silver ring contains $$2.80 	imes 10$$^{22}$$ silver atoms. How many moles of silver does it contain? (1$$\ 	ext{mol} = 6.022 	imes $$10^{23}$$ atoms)

Accepted Answer

$$4.65 	imes 10$$^{-2}$$\ 	ext{mol}$$

Question 8

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 9

A naturally occurring element consists of two isotopes: 75.77% isotope A (mass 34.97 amu) and 24.23% isotope B (mass 36.97 amu). What is the atomic mass of the element?

Accepted Answer

$$0.7577 	imes 34.97 + 0.2423 	imes 36.97 = 35.45\ 	ext{amu}$$

Question 10

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

Accepted Answer

Most of the atom is empty space.

Question 11

A cube of titanium contains $$2.86 	imes 10$$^{22}$$ atoms. The density of titanium is 4.50$$\ 	ext{g/cm}^3$$. What is the edge length of the cube? (Molar mass of Ti = 47.87$$\ 	ext{g/mol}$$, 1$$\ 	ext{mol} = 6.022 	imes $$10^{23}$$ atoms)

Accepted Answer

First, calculate moles: $$\frac{2.86 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.0475\ 	ext{mol}$$; mass: $$0.0475\ 	ext{mol} 	imes 47.87\ 	ext{g/mol} = 2.27\ 	ext{g}$$; volume: $$\frac{2.27\ 	ext{g}}{4.50\ 	ext{g/cm}^3} = 0.504\ 	ext{cm}^3$$; edge length: $$\sqrt[3]{0.504} = 0.795\ 	ext{cm}$$

Question 12

Which of the following is NOT a postulate of Dalton's atomic theory?

Accepted Answer

Atoms of one element can change into atoms of another element during a chemical reaction.

Question 13

A sample of carbon monoxide contains 17.2 g of oxygen and 12.9 g of carbon. Another sample contains 10.5 g of oxygen and 7.88 g of carbon. Are these results consistent with the law of definite proportions?

Accepted Answer

Yes, because $$\frac{17.2}{12.9} = 1.33$$ and $$\frac{10.5}{7.88} = 1.33$$, so the mass ratio is constant.

Question 14

Which of the following best describes a cation?

Accepted Answer

A positively charged ion formed when an atom loses electrons.

Question 15

How many atoms are present in a 3.10 g copper penny? (Molar mass of Cu = $$63.55\ 	ext{g/mol}$$, $$1\ 	ext{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$3.10\ 	ext{g} 	imes \frac{1\ 	ext{mol}}{63.55\ 	ext{g}} 	imes 6.022 	imes 10$$^{23}$$\ 	ext{atoms/mol} = 2.94 	imes 10$$^{22}$$ atoms

Question 16

Which of the following statements about the mole is correct?

Accepted Answer

A mole contains $$6.022 	imes 10$$^{23}$$ entities, which is Avogadro's number.

Atoms and the Structure of Matter: Foundations of General Chemistry

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