Q: Calculate the average atomic weight of chlorine if $$^{35}\mathrm{Cl}$$ has a mass of 34.97 amu (75.78% abundance) and $$^{37}\mathrm{Cl}$$ has a mass of 36.97 amu (24.22% abundance).

$$(0.7578 \times 34.97) + (0.2422 \times 36.97) = 35.45$$ amu

Question 1

Which experiment provided the first direct evidence for the existence of the electron, and what was the key observation?

Accepted Answer

Thomson's cathode ray tube experiment; cathode rays were deflected by electric and magnetic fields

Question 2

According to Dalton’s Atomic Theory, which statement is INCORRECT based on modern understanding?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 3

A neutral atom of $$^{13}\mathrm{C}$$ contains how many protons, neutrons, and electrons?

Accepted Answer

6 protons, 7 neutrons, 6 electrons

Question 4

Which law states that the total mass of substances present after a chemical reaction is the same as the mass before the reaction?

Accepted Answer

Law of Conservation of Mass

Question 5

A sample of a compound contains 24 g of carbon and 32 g of oxygen. If the compound is always found to have this ratio, which law does this illustrate?

Accepted Answer

Law of Constant Composition

Question 6

Which of the following best describes the difference between the Bohr and Schrödinger models of the atom?

Accepted Answer

Bohr’s model has electrons in fixed orbits; Schrödinger’s model describes electrons as probability clouds.

Question 7

Which element is a metalloid and is found along the steplike line on the periodic table?

Accepted Answer

Silicon (Si)

Question 8

Calculate the average atomic weight of chlorine if $$^{35}\mathrm{Cl}$$ has a mass of 34.97 amu (75.78% abundance) and $$^{37}\mathrm{Cl}$$ has a mass of 36.97 amu (24.22% abundance).

Accepted Answer

$$(0.7578 	imes 34.97) + (0.2422 	imes 36.97) = 35.45$$ amu

Question 9

Which of the following is a correct empirical formula for a compound with the molecular formula $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 10

Which of the following ions is a polyatomic cation?

Accepted Answer

$$\mathrm{NH}_4^+$$

Question 11

What is the correct name for $$\mathrm{FeCl}_3$$?

Accepted Answer

Iron(III) chloride

Question 12

Which of the following acids is correctly named?

Accepted Answer

$$\mathrm{H}_2\mathrm{SO}_4$$: sulfuric acid

Question 13

Which group on the periodic table contains the noble gases?

Accepted Answer

Group 8A (18)

Question 14

A sample contains two compounds of nitrogen and oxygen. In one, 14 g of nitrogen combines with 16 g of oxygen; in the other, 14 g of nitrogen combines with 32 g of oxygen. Which law does this illustrate?

Accepted Answer

Law of Multiple Proportions

Question 15

Which of the following is a diatomic molecule found naturally in the atmosphere?

Accepted Answer

$$\mathrm{N}_2$$

Question 16

What is the charge and composition of an alpha particle?

Accepted Answer

Charge +2, 2 protons and 2 neutrons

Question 17

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation is positively charged and forms when an atom loses electrons; an anion is negatively charged and forms when an atom gains electrons.

Question 18

Which of the following is the correct formula for ammonium sulfate?

Accepted Answer

$$(\mathrm{NH}_4)_2\mathrm{SO}_4$$

Question 19

Which of the following is the correct name for $$\mathrm{N}_2\mathrm{O}_5$$?

Accepted Answer

Dinitrogen pentoxide

Chapter 2 Atoms, Molecules, and Ions: Foundations of Modern Chemistry

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