Q: How many atoms are present in 2.00 moles of sodium ($$\mathrm{Na}$$)?

$$1.20 \times 10$$^{24}$$ atoms

Question 1

Which of the following statements best describes the law of conservation of mass as formulated by Antoine Lavoisier?

Accepted Answer

In a chemical reaction, the total mass of the substances involved does not change.

Question 2

Which experiment led to the discovery of the electron and the measurement of its charge-to-mass ratio?

Accepted Answer

J.J. Thomson's cathode ray tube experiment

Question 3

Which of the following is a correct representation of an isotope of carbon with 7 neutrons?

Accepted Answer

$$^{13}_{6}\mathrm{C}$$

Question 4

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

$$8.0:1$$

Question 5

Which of the following best explains why the gold foil experiment disproved the plum-pudding model of the atom?

Accepted Answer

Some alpha particles were deflected at large angles, indicating a dense, positively charged nucleus.

Question 6

Which group of elements is characterized by being mostly unreactive and having a full valence shell?

Accepted Answer

Noble gases (Group 8A)

Question 7

Which of the following is a property of metals?

Accepted Answer

They are good conductors of heat and electricity.

Question 8

How many protons, neutrons, and electrons are present in a neutral atom of $$^{24}_{12}\mathrm{Mg}$$?

Accepted Answer

12 protons, 12 neutrons, 12 electrons

Question 9

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons and has a positive charge.

Question 10

Which law is illustrated by the fact that carbon monoxide (CO) and carbon dioxide (CO$$_2) $$have oxygen-to-carbon mass ratios of 1.33:1 and 2.67:1, respectively?

Accepted Answer

Law of multiple proportions

Question 11

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

Accepted Answer

$$35.45\ \mathrm{amu}$$

Question 12

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 13

How many atoms are present in 2.00 moles of sodium ($$\mathrm{Na}$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 14

Which of the following best describes the difference between a molecule of water and its constituent atoms?

Accepted Answer

A water molecule is composed of two hydrogen atoms and one oxygen atom chemically bonded together.

Question 15

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 16

If you have 75.0 g of mercury (Hg), and the molar mass of Hg is 200.59 g/mol, how many moles of Hg do you have?

Accepted Answer

$$0.374\ \mathrm{mol}$$

Question 17

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 18

Which scientist is credited with the discovery of the neutron?

Accepted Answer

James Chadwick

Question 19

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

Accepted Answer

$$	ext{Average atomic mass} = (	ext{fractional abundance}_1 	imes 	ext{isotopic mass}_1) + (	ext{fractional abundance}_2 	imes 	ext{isotopic mass}_2)$$

Atoms and Elements: Foundations of Modern Atomic Theory

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