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

$$0.7577 \times 34.97 + 0.2423 \times 36.97 = 35.45$$ amu

Q: How many atoms are in 2.00 mol of magnesium?

$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.204 \times 10$$^{24}$$ atoms

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

$$\text{Atomic mass} = (\text{fraction}_1 \times \text{mass}_1) + (\text{fraction}_2 \times \text{mass}_2)$$

Question 1

Which experiment provided the first direct evidence for the existence of electrons as subatomic particles?

Accepted Answer

J.J. Thomson's cathode ray tube experiment

Question 2

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

Accepted Answer

Law of conservation of mass

Question 3

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

Accepted Answer

$$\frac{16.0}{2.0} = 8.0:1$$

Question 4

Which of the following statements is NOT part of Dalton’s atomic theory?

Accepted Answer

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

Question 5

Which of the following best explains why the mass of a helium atom is about four times that of a hydrogen atom?

Accepted Answer

Helium has two protons and two neutrons, while hydrogen has one proton and no neutrons.

Question 6

Which element is defined by having 17 protons in its nucleus?

Accepted Answer

Chlorine

Question 7

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

Accepted Answer

$$0.7577 	imes 34.97 + 0.2423 	imes 36.97 = 35.45$$ amu

Question 8

Which group of elements is characterized by being highly unreactive and is found in group 8A of the periodic table?

Accepted Answer

Noble gases

Question 9

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 10

A main-group element in group 2A will most likely form which ion?

Accepted Answer

$$2+$$ cation

Question 11

How many atoms are in 2.00 mol of magnesium?

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.204 	imes 10$$^{24}$$ atoms

Question 12

Which of the following best describes the difference between isotopes of the same element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 13

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

Accepted Answer

$$	ext{Atomic mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2)$$

Question 14

A cube of titanium contains $$2.86 	imes 10$$^{23}$$ atoms. If the density of titanium is 4.50$$ \ 	ext{g/cm}^3$$, what is the first step to find the edge length of the cube?

Accepted Answer

Calculate the mass of titanium using the number of atoms and molar mass.

Question 15

Which of the following best describes the periodic law?

Accepted Answer

When elements are arranged in order of increasing mass, certain sets of properties recur periodically.

Question 16

Which property is NOT characteristic of metals?

Accepted Answer

Poor conductors of heat and electricity

Question 17

A sample contains 2.80 $$	imes$$ $$10^{22}$$ silver atoms. How many moles of silver atoms does it contain?

Accepted Answer

$$\frac{2.80 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.0465$$ mol

Question 18

Which of the following ions is most likely formed by a halogen?

Accepted Answer

$$1-$$ anion

Question 19

Which scientist’s work led to the discovery of the neutron?

Accepted Answer

James Chadwick

Question 20

Which of the following is the correct sequence for converting the mass of a sample to the number of atoms?

Accepted Answer

Mass $$\rightarrow$$ Moles $$\rightarrow$$ Number of atoms

Atoms and Elements: Foundations of Modern Chemistry

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