Q: What is Avogadro's number, and what does it represent?

$$6.022 \times 10$$^{23}$$, the number of atoms in one mole of a substance

Q: Calculate the number of molecules in 2.00 moles of water ($$H_2O). $$Use Avogadro's number.

$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.2044 \times 10$$^{24}$$ molecules

Q: What is the molar mass of water ($$H_2O$$)?

$$2 \times 1.01 + 16.00 = 18.02 g/$$mol

Question 1

Which statement best describes Aristotle's view of matter around 384 B.C.E.?

Accepted Answer

All matter is composed of four elements and is continuous, not atomistic.

Question 2

Leucippus and Democritus introduced the concept of 'atomos.' What does 'atomos' mean?

Accepted Answer

'Atomos' refers to the point at which matter can no longer be subdivided.

Question 3

Which law states that during a chemical change, matter is neither created nor destroyed?

Accepted Answer

Law of Conservation of Mass

Question 4

A student decomposes 100.0 grams of mercury(II) oxide and obtains 92.61 grams of mercury and 7.39 grams of oxygen. Which law does this experiment best illustrate?

Accepted Answer

Law of Conservation of Mass

Question 5

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

Accepted Answer

A compound always contains the same elements in certain definite proportions.

Question 6

Copper carbonate is found in different locations around the world. According to the Law of Definite Proportions, what can be said about its composition?

Accepted Answer

It always has the same composition regardless of its source.

Question 7

Which experiment best illustrates the Law of Definite Proportions?

Accepted Answer

Combining lead and sulfur in different ratios and finding only one ratio forms lead sulfide.

Question 8

According to Dalton's Atomic Theory, which statement is correct?

Accepted Answer

Compounds are formed when atoms of different elements combine in fixed proportions.

Question 9

Which of the following is a modification to Dalton's Atomic Theory based on later discoveries?

Accepted Answer

Atoms of the same element can have different relative masses (isotopes).

Question 10

What is Avogadro's number, and what does it represent?

Accepted Answer

$$6.022 	imes 10$$^{23}$$, the number of atoms in one mole of a substance

Question 11

Calculate the number of molecules in 2.00 moles of water ($$H_2O). $$Use Avogadro's number.

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.2044 	imes 10$$^{24}$$ molecules

Question 12

What is the molar mass of water ($$H_2O$$)?

Accepted Answer

$$2 	imes 1.01 + 16.00 = 18.02 g/$$mol

Question 13

If you have 36.0 grams of water ($$H_2O$$), how many moles do you have? (Molar mass of $$H_2O is 18.0 g/$$mol)

Accepted Answer

$$\frac{36.0}{18.0} = 2.0$$ moles

Question 14

Which of the following best describes the Law of Multiple Proportions?

Accepted Answer

Elements may combine in more than one set of proportions, with each set corresponding to a different compound.

Question 15

Which of the following is an example of green chemistry?

Accepted Answer

Replacing mercury fluorescent light bulbs with efficient mercury-free light bulbs.

Question 16

Dmitri Mendeleev's periodic table was unique because he:

Accepted Answer

Arranged elements by increasing atomic mass and predicted properties of undiscovered elements.

Question 17

Which of the following is true about isotopes?

Accepted Answer

Isotopes are atoms of the same element with different relative masses.

Question 18

A diamond is burned in pure oxygen to produce carbon dioxide. If 12.01 grams of carbon are used, how many moles of $$CO_2$$ are produced? (Molar mass of $$CO_2 = 44.01 g/$$mol)

Accepted Answer

$$\frac{12.01}{12.01} = 1.00$$ mole of $$CO_2$$

Question 19

Which of the following best describes the main goal of green chemistry?

Accepted Answer

To replace rare or hazardous substances with more abundant or less hazardous substances.

Atoms, Laws of Chemical Combination, and the Periodic Table: Foundations of Chemistry

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