Q: Chlorine has two naturally occurring isotopes: $$^{35}Cl (34.97 $$amu, 75.77%) and $$^{37}Cl (36.97 $$amu, 24.23%). 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 6.03 mol of lead (Pb)? Use Avogadro’s number.

$$6.03 \times 6.022 \times 10$$^{23}$$ = 3.63 \times 10$$^{24}$$ atoms

Q: A platinum ring contains $$3.02 \times 10$$^{22}$$ platinum atoms. How many moles of platinum atoms does it contain?

$$3.02 \times 10$$^{22}$$ \div 6.022 \times 10$$^{23}$$ = 0.0501$$ mol

Q: What is the mass in grams of $$2.3 \times 10$$^{-3}$$ mol of antimony (Sb)? (Molar mass of Sb = 121.76 g/mol)

$$2.3 \times 10$$^{-3}$$ \times 121.76 = 0.28 g$$

Question 1

Which law states that the total mass remains constant during a chemical reaction, as illustrated by the reaction of sodium and chlorine to form sodium chloride?

Accepted Answer

Law of Conservation of Mass

Question 2

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

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

Question 3

Which statement best describes the Law of Definite Proportions?

Accepted Answer

All samples of a given compound have the same proportions of their constituent elements.

Question 4

Carbon dioxide and carbon monoxide are both compounds of carbon and oxygen. If the mass ratio of oxygen to carbon in CO$$_2 is 2.67$$:1 and in CO is 1.33:1, what is the ratio of these two masses?

Accepted Answer

$$\frac{2.67}{1.33} = 2$$

Question 5

Which of the following is NOT a postulate of Dalton’s Atomic Theory?

Accepted Answer

Atoms can be created or destroyed in chemical reactions.

Question 6

J.J. Thomson’s cathode ray experiment led to the discovery of which subatomic particle?

Accepted Answer

Electron

Question 7

Millikan’s oil drop experiment determined the charge of a single electron. What is the value of this charge?

Accepted Answer

$$-1.60 	imes 10$$^{-19}$$ C

Question 8

Which experiment disproved the Plum Pudding model and led to the discovery of the atomic nucleus?

Accepted Answer

Rutherford’s Gold Foil Experiment

Question 9

What is the atomic number (Z) of an element, and what does it represent?

Accepted Answer

The number of protons in the nucleus

Question 10

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 11

A neutral atom of sodium (Na) has an atomic number of 11. How many protons and electrons does it have?

Accepted Answer

11 protons and 11 electrons

Question 12

Which group on the periodic table contains the noble gases?

Accepted Answer

Group 8A

Question 13

Chlorine has two naturally occurring isotopes: $$^{35}Cl (34.97 $$amu, 75.77%) and $$^{37}Cl (36.97 $$amu, 24.23%). What is the atomic mass of chlorine?

Accepted Answer

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

Question 14

How many atoms are in 6.03 mol of lead (Pb)? Use Avogadro’s number.

Accepted Answer

$$6.03 	imes 6.022 	imes 10$$^{23}$$ = 3.63 	imes 10$$^{24}$$ atoms

Question 15

A platinum ring contains $$3.02 	imes 10$$^{22}$$ platinum atoms. How many moles of platinum atoms does it contain?

Accepted Answer

$$3.02 	imes 10$$^{22}$$ \div 6.022 	imes 10$$^{23}$$ = 0.0501$$ mol

Question 16

Calculate the amount of argon (Ar), in moles, contained in 11.8 grams of argon. (Molar mass of Ar = 39.95 g/mol)

Accepted Answer

$$11.8 \div 39.95 = 0.295$$ mol$

Question 17

What is the mass in grams of $$2.3 	imes 10$$^{-3}$$ mol of antimony (Sb)? (Molar mass of Sb = 121.76 g/mol)

Accepted Answer

$$2.3 	imes 10$$^{-3}$$ 	imes 121.76 = 0.28 g$$

Question 18

How many gold (Au) atoms are in a gold bar that is $$8.00 	ext{ cm} 	imes 2.00 	ext{ cm} 	imes 1.50 	ext{ cm}$$? (Density of Au = $$19.3 	ext{ g/cm}^3$$, Molar mass = $$197.0 	ext{ g/mol}$$, Avogadro’s number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

First, calculate the volume: $$8.00 	imes 2.00 	imes 1.50 = 24.0 	ext{ cm}^3. $$Then, mass: $$24.0 	imes 19.3 = 463.2 g. $$Moles: $$463.2 \div 197.0 = 2.352$$ mol. Atoms: $$2.352 	imes 6.022 	imes 10$$^{23}$$ = 1.42 	imes 10$$^{24}$$ atoms.

Question 19

Which of the following best describes the mole (mol) in chemistry?

Accepted Answer

The amount of material containing $$6.022 	imes 10$$^{23}$$ particles

Atoms and Elements: Foundations of Modern Chemistry

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