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

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

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 illustrated by the decomposition of 100.00 grams of mercuric oxide into 92.61 grams of mercury and 7.39 grams of oxygen, as shown in the first image?

Accepted Answer

The law of conservation of mass

Question 2

A student combines 10.00 g of lead with 3.00 g of sulfur and obtains 11.55 g of lead sulfide, with 1.45 g of sulfur left over. Which law does this experiment best demonstrate?

Accepted Answer

The law of definite proportions

Question 3

According to Dalton's atomic theory, which statement is NOT correct based on modern modifications?

Accepted Answer

All atoms of a given element are identical in mass and properties.

Question 4

Which of the following best describes Avogadro’s number?

Accepted Answer

The number of atoms, molecules, or formula units in one mole of a substance

Question 5

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

Accepted Answer

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

Question 6

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

Accepted Answer

$$5.75 \ \mathrm{g}$$

Question 7

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

Accepted Answer

$$0.018$$ moles

Question 8

What is the molar mass of carbon dioxide ($$\mathrm{CO}_2$$)? (Atomic masses: C = $$12.01 \ \mathrm{g/mol}$$, O = $$16.00 \ \mathrm{g/mol})$$

Accepted Answer

$$44.01 \ \mathrm{g/mol}$$

Question 9

How many moles of ammonia ($$\mathrm{NH}_3) $$are present in $$84.12 \ \mathrm{g} of $$ammonia? (Molar mass of $$\mathrm{NH}_3 = 17.03 \ \mathrm{g/mol})$$

Accepted Answer

$$4.94$$ moles

Question 10

Which of the following best explains why the periodic table developed by Mendeleev was so powerful for predicting new elements?

Accepted Answer

It organized elements by properties and left intentional gaps for undiscovered elements.

Question 11

A compound is always made up of the same elements in the same ratio by mass. Which law does this statement describe?

Accepted Answer

Law of definite proportions

Question 12

If 4 g of hydrogen reacts with 114 g of fluorine to produce 80 g of HF and 38 g of F are left over, what law is being demonstrated?

Accepted Answer

Law of conservation of mass

Question 13

Which of the following is a modern modification to Dalton’s atomic theory?

Accepted Answer

Atoms of a given element can have different masses (isotopes).

Question 14

A student is given 3.21 $$	imes$$ $$10^{-1} g of $$aluminum (Al). What portion of a mole is this? (Molar mass of Al = $$26.98 \ \mathrm{g/mol})$$

Accepted Answer

$$0.0119$$ moles

Question 15

Which of the following best describes a molecule?

Accepted Answer

A group of chemically bonded atoms in an exact proportion

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 real-world scenario best illustrates the law of multiple proportions?

Accepted Answer

Carbon and oxygen can form both CO and CO$$_2$$, with different mass ratios of oxygen to carbon.

Atoms and Atomic Theory: Laws, Mole Concept, and the Periodic Table

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