Q: A sample contains 75% $$^{35}\mathrm{Cl} ($$atomic mass = 34.97 u) and 25% $$^{37}\mathrm{Cl} ($$atomic mass = 36.97 u). What is the average atomic mass of chlorine?

$$(0.75 \times 34.97) + (0.25 \times 36.97) = 35.47\ \mathrm{u}$$

Question 1

Which of the following statements best describes the Law of Definite Proportions?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

A sample of magnesium reacts completely with oxygen to form 40.3 g of magnesium oxide. If the reaction started with 24.3 g of magnesium, what mass of oxygen reacted? (Law of Conservation of Mass)

Accepted Answer

$$40.3\ \mathrm{g} - 24.3\ \mathrm{g} = 16.0\ \mathrm{g}$$

Question 3

Which of the following is a transition metal?

Accepted Answer

Fe

Question 4

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 5

A chlorine atom has 17 protons and 18 neutrons. What is its mass number?

Accepted Answer

$$17 + 18 = 35$$

Question 6

Which experiment provided evidence for the existence of the electron?

Accepted Answer

Thomson's cathode ray tube experiment

Question 7

A sample contains 75% $$^{35}\mathrm{Cl} ($$atomic mass = 34.97 u) and 25% $$^{37}\mathrm{Cl} ($$atomic mass = 36.97 u). What is the average atomic mass of chlorine?

Accepted Answer

$$(0.75 	imes 34.97) + (0.25 	imes 36.97) = 35.47\ \mathrm{u}$$

Question 8

Which of the following is a correct representation of a chemical formula for a diatomic molecule?

Accepted Answer

$$\mathrm{O}_2$$

Question 9

Which of the following statements about covalent bonds is correct?

Accepted Answer

Covalent bonds involve the sharing of electron pairs between atoms.

Question 10

How many moles are in 18.0 g of water ($$\mathrm{H}_2\mathrm{O}$$)? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{18.0\ \mathrm{g}}{18.0\ \mathrm{g/mol}} = 1.0\ \mathrm{mol}$$

Question 11

Which of the following best describes a mixture?

Accepted Answer

A combination of two or more substances that retain their individual properties.

Question 12

Which of the following is a main group element?

Accepted Answer

Mg

Question 13

Which of the following is the correct electron configuration for a neutral atom of carbon ($$Z=6$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^2$$

Question 14

Which of the following is a property of metals?

Accepted Answer

They are good conductors of electricity.

Question 15

Which of the following best describes Rutherford's gold foil experiment?

Accepted Answer

It showed that atoms have a small, dense, positively charged nucleus.

Question 16

Which of the following is the correct name for $$\mathrm{Na}_2\mathrm{SO}_4$$?

Accepted Answer

Sodium sulfate

Question 17

Which of the following is a correct example of the Law of Multiple Proportions?

Accepted Answer

CO and CO$$_2$$ both contain carbon and oxygen, but in different ratios by mass.

Question 18

How many protons, neutrons, and electrons are in $$^{23}\mathrm{Na}^+$$?

Accepted Answer

11 protons, 12 neutrons, 10 electrons

Question 19

Which of the following is a correct statement about Avogadro's number?

Accepted Answer

It is the number of particles in one mole, $$6.022 	imes 10$$^{23}$$.

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