Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average mass} = (x_1$ \times m_1$) + (x_2$ \times m_2$)$$

Q: A sample contains 3.00 mol of carbon atoms. How many atoms are present in the sample?

$$3.00 \times 6.022 \times 10$$^{23}$$ = 1.81 \times 10$$^{24}$$ atoms

Question 1

Which of the following best describes a chemical change?

Accepted Answer

Iron rusting in the presence of oxygen

Question 2

Which law states that matter is neither created nor destroyed in a chemical reaction?

Accepted Answer

Law of Conservation of Mass

Question 3

A sample of pure water is decomposed into 2.0 g of hydrogen and 16.0 g of oxygen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0}{2.0} = 8.0$$

Question 4

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 5

Which of the following is a derived SI unit?

Accepted Answer

Joule (J)

Question 6

A student measures the mass of a sample three times and gets values of 2.51 g, 2.50 g, and 2.52 g. The true mass is 2.00 g. Which statement best describes the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 7

Which of the following best explains why sodium metal (Na) is highly reactive, but sodium ions (Na$$^+) $$are relatively inert?

Accepted Answer

Sodium atoms have a single valence electron that is easily lost, while sodium ions have a stable electron configuration.

Question 8

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average mass} = (x_1$ 	imes m_1$) + (x_2$ 	imes m_2$)$$

Question 9

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

Accepted Answer

Thomson's cathode ray tube experiment

Question 10

A gold atom has an atomic number of 79 and a mass number of 197. How many neutrons does a gold atom have?

Accepted Answer

118

Question 11

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 12

Which of the following is NOT a property of metals as described in the periodic table?

Accepted Answer

Tends to gain electrons to form anions

Question 13

A sample contains 3.00 mol of carbon atoms. How many atoms are present in the sample?

Accepted Answer

$$3.00 	imes 6.022 	imes 10$$^{23}$$ = 1.81 	imes 10$$^{24}$$ atoms

Question 14

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

Accepted Answer

It demonstrated that most of the atom's mass and positive charge are concentrated in a small nucleus.

Question 15

Which of the following is the correct number of significant figures in the measurement 0.0540 g?

Accepted Answer

3

Question 16

A student converts 25.0 cm to inches using the conversion factor $$1 	ext{ in} = 2.54 	ext{ cm}. $$What is the correct answer, with the proper number of significant figures?

Accepted Answer

$$9.84 in$$

Question 17

Which of the following best describes a physical property?

Accepted Answer

The boiling point of water

Question 18

Which of the following is the correct SI prefix for $$10^{-6}$$?

Accepted Answer

micro-

Question 19

Which of the following best explains why noble gases are unreactive?

Accepted Answer

They have a full complement of valence electrons, making them stable.

Question 20

A sample of chlorine consists of 75.77% $$^{35}Cl ($$mass = 34.968853 amu) and 24.23% $$^{37}Cl ($$mass = 36.965903 amu). What is the average atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.968853) + (0.2423 	imes 36.965903) = 35.45$$ amu

Measurement, Physical and Chemical Change: Foundations of General Chemistry

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