Q: A naturally occurring element has two isotopes: 75% with a mass of 35 amu and 25% with a mass of 37 amu. What is the atomic mass of the element?

$$0.75 \times 35 + 0.25 \times 37 = 35.5$$ amu

Q: How many atoms are present in 2.00 mol of helium?

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

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

$$\text{Atomic mass} = \sum (\text{fraction of isotope n}) \times (\text{mass of isotope n})$$

Q: A neutral atom of sodium (Na) has 11 protons and 12 neutrons. What is its mass number and isotope symbol?

Mass number = 23; Symbol = $$^{23}_{11}\text{Na}$$

Question 1

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound is made of two or more elements chemically bonded in fixed proportions, while a mixture contains two or more substances physically combined in variable proportions.

Question 2

Which law is demonstrated when 7.7 g of Na reacts with 11.9 g of Cl$$_2 to $$produce 19.6 g of NaCl, with no mass lost or gained?

Accepted Answer

Law of Conservation of Mass

Question 3

A sample of carbon monoxide contains 1.33 g of oxygen per 1 g of carbon, while carbon dioxide contains 2.67 g of oxygen per 1 g of carbon. What is the ratio of the masses of oxygen that combine with a fixed mass of carbon in these two compounds?

Accepted Answer

$$\frac{2.67}{1.33} = 2.01$$

Question 4

Which experiment provided evidence for the existence of the nucleus in the atom?

Accepted Answer

Rutherford’s gold foil experiment

Question 5

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 6

A neutral atom of chlorine has an atomic number of 17 and a mass number of 37. How many protons, neutrons, and electrons does it contain?

Accepted Answer

17 protons, 20 neutrons, 17 electrons

Question 7

Which property of gases allows them to be compressed, as shown in the piston experiment?

Accepted Answer

The particles in a gas are widely spaced and can be forced closer together.

Question 8

Which of the following is a homogeneous mixture?

Accepted Answer

Sweetened tea

Question 9

Which subatomic particle was discovered by J.J. Thomson using the cathode ray tube experiment?

Accepted Answer

Electron

Question 10

A naturally occurring element has two isotopes: 75% with a mass of 35 amu and 25% with a mass of 37 amu. What is the atomic mass of the element?

Accepted Answer

$$0.75 	imes 35 + 0.25 	imes 37 = 35.5$$ amu

Question 11

How many atoms are present in 2.00 mol of helium?

Accepted Answer

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

Question 12

Which of the following best explains why isotopes of the same element have different masses?

Accepted Answer

They have different numbers of neutrons.

Question 13

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

Accepted Answer

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

Question 14

A neutral atom of sodium (Na) has 11 protons and 12 neutrons. What is its mass number and isotope symbol?

Accepted Answer

Mass number = 23; Symbol = $$^{23}_{11}	ext{Na}$$

Question 15

Which of the following statements about the plum-pudding model is correct?

Accepted Answer

It proposed that electrons are embedded in a sphere of positive charge.

Question 16

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons and is positively charged.

Question 17

Which experiment determined the charge of a single electron?

Accepted Answer

Millikan’s oil drop experiment

Question 18

How many moles of carbon are present in 24.02 g of carbon? (Atomic mass of C = 12.01 g/mol)

Accepted Answer

$$\frac{24.02}{12.01} = 2.00$$ mol

Question 19

Which of the following is NOT a property of a solid?

Accepted Answer

Particles are widely spaced and compressible.

Atoms and the Structure of Matter: General Chemistry Chapter 1 Study Notes

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