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

A mole is a specific number, $$6.022 \times 10$$^{23}$$, of atoms, molecules, or formula units.

Q: How many atoms are present in 2.00 moles of magnesium ($$Mg$$)?

$$1.20 \times 10$$^{24}$$ atoms$$\ (2.00\ mol \times 6.022 \times $$10^{23}$$\ atoms/mol)$$

Q: A sample contains $$1.50 \times 10$$^{24}$$ molecules of CO_2$. How many moles of CO_2$ are present?

$$2.49$$ moles$$\ \left(\frac{1.50 \times 10$$^{24}$$}{6.022 \times 10$$^{23}$$}\right)$$

Q: What is the mass (in grams) of $$0.750$$ moles of $$NaCl$$? ($$Na = 22.99\ g/mol$$, $$Cl = 35.45\ g/mol)$$

$$43.8 g$\ (0.750\ mol \times 58.44\ g/mol)$$

Q: A can contains $$16.2$$ grams of aluminum ($$Al). $$How many atoms of aluminum are in the can? ($$Al = 26.98\ g/mol)$$

$$3.62 \times 10$$^{23}$$ atoms

Q: Which of the following is the correct formula to calculate mass percent composition?

$$\text{mass percent} = \frac{\text{mass of element in 1 mol of compound}}{\text{mass of 1 mol of compound}} \times 100\%$$

Question 1

Which of the following statements best describes the mole in chemistry?

Accepted Answer

A mole is a specific number, $$6.022 	imes 10$$^{23}$$, of atoms, molecules, or formula units.

Question 2

How many atoms are present in 2.00 moles of magnesium ($$Mg$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms$$\ (2.00\ mol 	imes 6.022 	imes $$10^{23}$$\ atoms/mol)$$

Question 3

A sample contains $$1.50 	imes 10$$^{24}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$2.49$$ moles$$\ \left(\frac{1.50 	imes 10$$^{24}$$}{6.022 	imes 10$$^{23}$$}ight)$$

Question 4

What is the mass (in grams) of $$0.750$$ moles of $$NaCl$$? ($$Na = 22.99\ g/mol$$, $$Cl = 35.45\ g/mol)$$

Accepted Answer

$$43.8 g$\ (0.750\ mol 	imes 58.44\ g/mol)$$

Question 5

A can contains $$16.2$$ grams of aluminum ($$Al). $$How many atoms of aluminum are in the can? ($$Al = 26.98\ g/mol)$$

Accepted Answer

$$3.62 	imes 10$$^{23}$$ atoms

Question 6

Calculate the mass percent of chlorine in $$CCl_4$$. ($$C = 12.01\ g/mol$$, $$Cl = 35.45\ g/mol)$$

Accepted Answer

$$85.0\%$$

Question 7

A $$0.358-$$gram sample of chromium reacts with oxygen to form $$0.523$$ grams of chromium oxide. What is the mass percent of chromium in the oxide?

Accepted Answer

$$68.5\%$$

Question 8

How many grams of sodium chloride ($$NaCl) $$can you consume and still be within the FDA sodium guideline of $$2.3$$ grams of sodium per day? ($$NaCl is$$ $$39\%$$ sodium by mass.)

Accepted Answer

$$5.9 g$$

Question 9

A $$3.24-$$gram sample of titanium reacts with oxygen to form $$5.40$$ grams of the metal oxide. What is the mass of oxygen in the oxide?

Accepted Answer

$$2.16 g$$

Question 10

Which of the following is the correct empirical formula for a compound containing $$60.00\% C$$, $$4.48\% H$$, and $$35.53\% O by $$mass?

Accepted Answer

$$C_9H_8O_4 ($$aspirin)

Question 11

A sample of water is decomposed to produce $$3.0$$ grams of hydrogen and $$24$$ grams of oxygen. What is the empirical formula of water based on these data?

Accepted Answer

$$H_2O$$

Question 12

What is the molecular formula of a compound with an empirical formula $$CH_2O$$ and a molar mass of $$180.2 g/$$mol?

Accepted Answer

$$C_6H_{12}O_6$

Question 13

How many moles of oxygen atoms are in $$1.7$$ moles of $$CaCO_3$$?

Accepted Answer

$$5.1$$ moles

Question 14

What is the mass of $$4.78 	imes 10$$^{24}$$ molecules of NO_2$? (N = 14.01$$\ g/mol$$, O = 16.00$$\ g/mol$$)

Accepted Answer

$$365 g$$

Question 15

Which of the following best describes the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is always a whole-number multiple of the empirical formula.

Question 16

If a compound contains $$12.01 g of $$carbon, how many moles of carbon does it contain?

Accepted Answer

$$1.00$$ mol

Question 17

Which of the following is the correct formula to calculate mass percent composition?

Accepted Answer

$$	ext{mass percent} = \frac{	ext{mass of element in 1 mol of compound}}{	ext{mass of 1 mol of compound}} 	imes 100\%$$

Question 18

Which of the following is NOT a correct use of Avogadro’s number?

Accepted Answer

To convert between grams and moles

Question 19

A $$0.58 g $$diamond is pure carbon. How many moles of carbon does it contain? ($$C = 12.01\ g/mol)$$

Accepted Answer

$$4.8 	imes 10$$^{-2}$$ mol

Chapter 6: Chemical Composition – Study Notes

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