Q: 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, and which law does this illustrate?

$$\text{Ratio} = 8:1$$, Law of Definite Proportions

Q: How many atoms are in 2.00 moles of magnesium ($$\text{Mg}$$)? (Avogadro’s number $$= 6.022 \times 10$$^{23}$$ atoms/mol)

$$1.20 \times 10$$^{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 law states that the total mass of reactants in a chemical reaction is equal to the total mass of the products?

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, and which law does this illustrate?

Accepted Answer

$$	ext{Ratio} = 8:1$$, Law of Definite Proportions

Question 3

Which experiment led to the discovery that atoms are mostly empty space with a small, dense, positively charged nucleus?

Accepted Answer

Rutherford’s Gold Foil Experiment

Question 4

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

Accepted Answer

Atoms can be created or destroyed in chemical reactions.

Question 5

A naturally occurring element consists of two isotopes: 70% with mass 10 amu and 30% with mass 11 amu. What is the atomic mass of the element?

Accepted Answer

$$10.3\ 	ext{amu}$$

Question 6

Which group in the periodic table contains elements that are chemically inert and do not readily form compounds?

Accepted Answer

Noble gases

Question 7

Which scientist is credited with formulating the law of conservation of mass?

Accepted Answer

Antoine Lavoisier

Question 8

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons

Question 9

If 12 g of carbon reacts with 16 g of oxygen to form CO and with 32 g of oxygen to form CO$$_2$$, what is the ratio of the masses of oxygen that combine with a fixed mass of carbon? Which law does this support?

Accepted Answer

$$2:1$$, Law of Multiple Proportions

Question 10

Which property is characteristic of metalloids?

Accepted Answer

They exhibit mixed properties of metals and nonmetals.

Question 11

How many atoms are in 2.00 moles of magnesium ($$	ext{Mg}$$)? (Avogadro’s number $$= 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 12

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have different numbers of neutrons.

Question 13

Which scientist arranged the periodic table by increasing atomic mass and predicted the existence of undiscovered elements?

Accepted Answer

Dmitri Mendeleev

Question 14

A sample contains $$3.00$$ grams of carbon ($$	ext{C}). $$The molar mass of carbon is $$12.01 g/$$mol. How many moles of carbon are present?

Accepted Answer

$$0.250$$ mol

Question 15

Which of the following is a main-group element?

Accepted Answer

Sodium ($$	ext{Na})$$

Question 16

Which of the following best describes the periodic law?

Accepted Answer

Elements are arranged in order of increasing atomic number, and properties recur periodically.

Question 17

Which subatomic particle was discovered by J.J. Thomson using cathode ray tubes?

Accepted Answer

Electron

Question 18

Which group in the periodic table contains elements that tend to lose one electron to form $$+1$$ ions?

Accepted Answer

Alkali metals

Question 19

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 20

Which of the following best explains why the periodic table is arranged in columns called groups?

Accepted Answer

Elements in the same group have similar chemical properties.

Atoms and Elements: Foundations of Modern Atomic Theory

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