Q: A sample contains 75.77% chlorine-35 (mass 34.97 amu) and 24.23% chlorine-37 (mass 36.97 amu). What is the atomic mass of chlorine?

$$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45\ \mathrm{amu}$$

Q: How many atoms are in 2.00 moles of copper?

$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.20 \times 10$$^{24}$$ atoms

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

Which of the following statements about the states of matter is correct?

Accepted Answer

Gases are compressible because their particles have a lot of space between them.

Question 3

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 in water?

Accepted Answer

$$\frac{16.0\ \mathrm{g}\ O}{2.0\ \mathrm{g}\ H} = 8.0$$

Question 4

Which experiment led to the discovery that atoms have a small, dense nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 5

Which of the following is a homogeneous mixture?

Accepted Answer

Salt dissolved in water

Question 6

According to Dalton’s atomic theory, which statement is NOT correct?

Accepted Answer

Atoms of the same element always have the same mass.

Question 7

A neutral atom of potassium-39 ($$^{39}_{19}\mathrm{K}) $$has how many protons, neutrons, and electrons?

Accepted Answer

19 protons, 20 neutrons, 19 electrons

Question 8

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

Accepted Answer

When two elements form two different compounds, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Question 9

A sample contains 75.77% chlorine-35 (mass 34.97 amu) and 24.23% chlorine-37 (mass 36.97 amu). What is the atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45\ \mathrm{amu}$$

Question 10

Which of the following is NOT a characteristic of a scientific theory?

Accepted Answer

It is a brief statement that summarizes past observations and predicts future ones.

Question 11

How many atoms are in 2.00 moles of copper?

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{24}$$ atoms

Question 12

Which of the following best explains why gases are compressible but solids are not?

Accepted Answer

Gas particles have much more space between them than solid particles.

Question 13

A sample of an element has a mass of 12.0 g. If the molar mass of the element is 24.0 g/mol, how many moles are present?

Accepted Answer

$$\frac{12.0\ \mathrm{g}}{24.0\ \mathrm{g/mol}} = 0.500\ \mathrm{mol}$$

Question 14

Which of the following is an example of a heterogeneous mixture?

Accepted Answer

Muddy water

Question 15

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 16

Which of the following is the correct formula for calculating the atomic mass of an element from its isotopes?

Accepted Answer

$$	ext{Atomic mass} = \sum_n (	ext{fraction of isotope } n 	imes 	ext{mass of isotope } n)$$

Question 17

A neutral atom of fluorine has 9 protons. If it gains one electron, what is the resulting charge and number of electrons?

Accepted Answer

Charge: $$-1$$, Electrons: $$10$$

Question 18

Which of the following best describes a scientific law?

Accepted Answer

A concise statement that summarizes past observations and predicts future ones, without explaining why.

Chapter 1: Atoms – Foundations of Matter and Atomic Theory

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