$$9.88 \times 10$$^{22}$$ atoms

$$\frac{\text{mass of element}}{\text{total mass of compound}} \times 100$$

$$1 \text{ mol} = 1 \text{ gram}$$

Question 1

Which of the following best defines Avogadro’s number?

Accepted Answer

The number of atoms in 12 grams of carbon-12

Question 2

A sample contains $$3.4$$ grams of lead ($$Pb). $$How many atoms of lead are present in the sample? (Molar mass of $$Pb = 207.2 g/$$mol)

Accepted Answer

$$9.88 	imes 10$$^{22}$$ atoms

Question 3

Which statement about the mole is correct?

Accepted Answer

A mole is Avogadro’s number of atoms, molecules, or ions

Question 4

What is the molar mass of $$AlCl_3$$?

Accepted Answer

$$133.33 g/$$mol

Question 5

How many moles of $$Cl$$ are present in $$0.243 g of$$ $$AlCl_3$$? (Molar mass of $$AlCl_3 = 133.33$ g/mol)

Accepted Answer

$$0.00546$$ mol

Question 6

A compound contains $$15.55\%$$ tin and $$54.45\%$$ chlorine by mass. What is its empirical formula?

Accepted Answer

$$SnCl_2$$

Question 7

If a compound has the empirical formula $$CH_2O$$ and a molar mass of $$180 g/$$mol, what is its molecular formula?

Accepted Answer

$$C_6H_{12}O_6$

Question 8

Calculate the percent composition of sulfur in $$PbSO_4 ($$Molar mass: $$Pb = 207.2 g/$$mol, $$S = 32.07 g/$$mol, $$O = 4 	imes 16.00 g/$$mol).

Accepted Answer

$$10.57\%$$

Question 9

A $$5$$ gram sample of sulfuric acid ($$H_2SO_4) is $$analyzed. How many moles of hydrogen are present? (Molar mass of $$H_2SO_4 = 98.09 g/$$mol)

Accepted Answer

$$0.102$$ mol$

Question 10

Which of the following is the correct sequence for converting grams of a substance to number of atoms?

Accepted Answer

Grams $$\rightarrow$$ Moles $$\rightarrow$$ Atoms

Question 11

A compound is found to have $$40.0\% C$$, $$6.67\% H$$, and $$53.33\% O by $$mass. What is its empirical formula?

Accepted Answer

$$CH_2O$$

Question 12

How many moles of $$Na$$ are present in $$10 g of $$sodium? (Molar mass of $$Na = 22.99 g/$$mol)

Accepted Answer

$$0.435$$ mol$

Question 13

Which of the following is true about empirical and molecular formulas?

Accepted Answer

Empirical formula shows the simplest whole-number ratio of elements

Question 14

What is the percent by mass of chlorine in $$AlCl_3$$? (Molar mass: $$Al = 26.98 g/$$mol, $$Cl = 35.45 g/$$mol)

Accepted Answer

$$79.8\%$$

Question 15

A compound has the empirical formula $$CHCl_3$$ and a molar mass of $$545 g/$$mol. What is its molecular formula?

Accepted Answer

$$C_9H_9Cl_{27}$$

Question 16

How many moles of $$Pb$$ are present in $$3.4$$ grams of lead? (Molar mass of $$Pb = 207.2 g/$$mol)

Accepted Answer

$$0.0164$$ mol$

Question 17

Which of the following is the correct formula for calculating percent composition by mass?

Accepted Answer

$$\frac{	ext{mass of element}}{	ext{total mass of compound}} 	imes 100$$

Question 18

If you have $$0.100$$ moles of $$H_3PO_4$$, how many moles of $$H^+$$ ions can be produced?

Accepted Answer

$$0.300$$ mol$

Question 19

Which of the following is NOT a correct conversion factor for mole calculations?

Accepted Answer

$$1 	ext{ mol} = 1 	ext{ gram}$$

Question 20

Which of the following statements about Avogadro’s number is correct?

Accepted Answer

It is a very large number used to count atoms, molecules, or ions in a mole

Chapter 6: Chemical Composition – Study Notes

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