Q: How many atoms are in $$0.345$$ mole of argon (Ar)? (Avogadro’s number = $$6.022 \times 10$$^{23}$$)

$$2.08 \times 10$$^{23}$$ atoms

Q: Which of the following best describes a mole in chemistry?

The amount of substance that contains $$6.022 \times 10$$^{23}$$ entities

Q: Which of the following is the correct relationship for converting between mass and number of atoms?

$$\text{Mass} \xrightarrow{\div \text{Molar mass}} \text{Moles} \xrightarrow{\times \text{Avogadro's number}} \text{Number of atoms}$$

Question 1

Which scientific law is best demonstrated by the reaction: 100.00 grams of mercuric oxide decomposes to form 92.61 grams of mercury and 7.39 grams of oxygen?

Accepted Answer

The law of conservation of mass

Question 2

A compound always contains the same elements in the same ratio by mass. Which law does this statement describe?

Accepted Answer

The law of definite proportions

Question 3

If 10.00 g of lead reacts with 1.55 g of sulfur to form 11.55 g of lead sulfide, but 10.00 g of lead reacts with 3.00 g of sulfur to form 11.55 g of lead sulfide and 1.45 g of sulfur is left over, what does this experiment illustrate?

Accepted Answer

The law of definite proportions

Question 4

Which of the following is NOT a postulate of Dalton’s original atomic theory?

Accepted Answer

Atoms can be divided into smaller particles

Question 5

Which modern modification to Dalton’s atomic theory is correct?

Accepted Answer

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

Question 6

A sample contains $$1.1 	imes 10$$^{22}$$ atoms of silver. How many moles of silver are present in the sample? (Avogadro’s number = 6.022$$ 	imes $$10^{23})$$

Accepted Answer

$$0.018$$ moles

Question 7

What is the mass of $$0.250$$ mol of sodium (Na)? (Molar mass of Na = $$22.99 g/$$mol)

Accepted Answer

$$5.75 g$$

Question 8

How many atoms are in $$0.345$$ mole of argon (Ar)? (Avogadro’s number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$2.08 	imes 10$$^{23}$$ atoms

Question 9

What is the molar mass of carbon dioxide ($$CO_2$$)? (Atomic masses: C = $$12.01 g/$$mol, O = $$16.00 g/$$mol)

Accepted Answer

$$44.01 g/$$mol

Question 10

How many moles of ammonia ($$NH_3) $$are present in $$84.12 g of$$ $$NH_3$$? (Molar mass of $$NH_3 = 17.03$ g/mol)

Accepted Answer

$$4.94$$ moles

Question 11

Which of the following best describes a mole in chemistry?

Accepted Answer

The amount of substance that contains $$6.022 	imes 10$$^{23}$$ entities

Question 12

Which experiment would best demonstrate the law of multiple proportions?

Accepted Answer

Reacting carbon with oxygen to form both $$CO$$ and $$CO_2$$

Question 13

If you have $$3.21 	imes 10$$^{-1}$$ g of aluminum (Al), how many moles of Al do you have? (Molar mass of Al = 26.98$ g/mol)

Accepted Answer

$$0.0119$$ moles

Question 14

Which of the following statements about Mendeleev’s periodic table is correct?

Accepted Answer

He left gaps for elements that had not yet been discovered

Question 15

A chemical reaction involves which of the following according to Dalton’s atomic theory?

Accepted Answer

A rearrangement of atoms

Question 16

Which of the following is the correct relationship for converting between mass and number of atoms?

Accepted Answer

$$	ext{Mass} \xrightarrow{\div 	ext{Molar mass}} 	ext{Moles} \xrightarrow{	imes 	ext{Avogadro's number}} 	ext{Number of atoms}$$

Question 17

Which of the following best explains why the atomic masses of elements are not whole numbers?

Accepted Answer

Elements exist as mixtures of isotopes with different masses

Question 18

A student claims that 1 mole of sodium chloride ($$NaCl) $$contains $$6.022 	imes 10$$^{23}$$ sodium atoms. What is wrong with this statement?

Accepted Answer

1 mole of $$NaCl$$ contains $$6.022 	imes 10$$^{23}$$ formula units, not sodium atoms

CH.2:Atoms, Molecules, and the Foundations of Chemical Laws

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