Q: How many atoms are present in 10.0 moles of magnesium (Mg)? (Avogadro’s number $$ = 6.022 \times 10$$^{23}$$ $$ atoms/mol)

$$ 6.022 \times 10$$^{24}$$ $$ atoms

Q: A lead sample has a mass of 207.2 g. How many lead atoms are present in the sample? (Atomic mass of Pb = 207.2 g/mol)

$$ 6.022 \times 10$$^{23}$$ $$ atoms

Q: How many molecules are present in $$ 2.50 $$ moles of $$ CO_2$ $$? (Avogadro’s number $$ = 6.022 \times 10$$^{23}$$ $$ molecules/mol)

$$ 1.51 \times 10$$^{24}$$ $$ molecules

Q: Given the balanced equation: $$ 4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s) $$, what is the correct mol-to-mol conversion factor between $$ Fe $$ and $$ O_2$ $$?

$$ \frac{4 \text{ mol } Fe}{3 \text{ mol } O_2$} $$

Q: Which of the following is the correct formula to calculate the mass percent of an element X in a compound?

$$ \frac{\text{Mass of element X in 1 mole of compound}}{\text{Mass of 1 mole of compound}} \times 100\% $$

Q: In the reaction $$ N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g) $$, what is the correct mol-to-mol conversion factor between $$ NH_3$ $$ and $$ H_2$ $$?

$$ \frac{2 \text{ mol } NH_3$}{3 \text{ mol } H_2$} $$

Q: Which of the following is a correct mol-to-mass conversion factor for $$ H_2$ $$ gas?

$$ \frac{2.016 \text{ g } H_2$}{1 \text{ mol } H_2$} $$

Question 1

Which of the following statements best describes the relationship between formula mass and molar mass for a compound?

Accepted Answer

Molar mass is numerically equivalent to formula mass, but expressed in g/mol instead of amu.

Question 2

Calculate the molar mass of ammonium phosphate, $$ (NH_4$)_3PO_4 $$, to two decimal places. (Atomic masses: N = 14.01 g/mol, H = 1.008 g/mol, P = 30.97 g/mol, O = 16.00 g/mol)

Accepted Answer

$$ 149.09 	ext{ g/mol} $$

Question 3

A sample contains 43.67 g of silicon (Si). What is the number of moles of silicon in the sample? (Atomic mass of Si = 28.09 g/mol)

Accepted Answer

$$ 1.56 	ext{ mol} $$

Question 4

How many atoms are present in 10.0 moles of magnesium (Mg)? (Avogadro’s number $$ = 6.022 	imes 10$$^{23}$$ $$ atoms/mol)

Accepted Answer

$$ 6.022 	imes 10$$^{24}$$ $$ atoms

Question 5

A lead sample has a mass of 207.2 g. How many lead atoms are present in the sample? (Atomic mass of Pb = 207.2 g/mol)

Accepted Answer

$$ 6.022 	imes 10$$^{23}$$ $$ atoms

Question 6

What is the mass (in grams) of $$ 0.328 $$ moles of ammonia ($$ NH_3$ $$)? (Molar mass of $$ NH_3$ = 17.03  g/$$mol)

Accepted Answer

$$ 5.58 	ext{ g} $$

Question 7

How many molecules are present in $$ 2.50 $$ moles of $$ CO_2$ $$? (Avogadro’s number $$ = 6.022 	imes 10$$^{23}$$ $$ molecules/mol)

Accepted Answer

$$ 1.51 	imes 10$$^{24}$$ $$ molecules

Question 8

A compound contains 81.68% C and 18.32% H by mass. What is the empirical formula of the compound?

Accepted Answer

$$ CH_2$ $$

Question 9

Given the balanced equation: $$ 4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s) $$, what is the correct mol-to-mol conversion factor between $$ Fe $$ and $$ O_2$ $$?

Accepted Answer

$$ \frac{4 	ext{ mol } Fe}{3 	ext{ mol } O_2$} $$

Question 10

What is the mass percent of chlorine in methylene chloride ($$ CH_2Cl_2 $$)? (Atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, Cl = 35.45 g/mol)

Accepted Answer

$$ 84.93\% $$

Question 11

A compound contains 24.5 g of nitrogen and 70.0 g of oxygen. What is the empirical formula of the compound? (Atomic masses: N = 14.01 g/mol, O = 16.00 g/mol)

Accepted Answer

$$ N_2O_5 $$

Question 12

If you have $$ 9.00 $$ moles of $$ Al_2O_3 $$, how many moles of aluminum atoms are present?

Accepted Answer

$$ 18.0 $$ moles

Question 13

What is the mass of carbon in $$ 5.98  g of $$propane ($$ C_3H_8 $$)? (Molar mass of $$ C_3H_8 = 44.10  g/$$mol, C = 12.01 g/mol)

Accepted Answer

$$ 1.63 	ext{ g} $$

Question 14

Which of the following is the correct formula to calculate the mass percent of an element X in a compound?

Accepted Answer

$$ \frac{	ext{Mass of element X in 1 mole of compound}}{	ext{Mass of 1 mole of compound}} 	imes 100\% $$

Question 15

A sample contains $$ 9.53 	imes 10$$^{21}$$ $$ molecules of $$ CO_2$ . $$What is the mass of the sample in grams? (Molar mass of $$ CO_2$ = 44.01  g/$$mol, Avogadro’s number $$ = 6.022 	imes 10$$^{23}$$ $$ molecules/mol)

Accepted Answer

$$ 0.697 	ext{ g} $$

Question 16

Which of the following best describes Avogadro’s number?

Accepted Answer

The number of particles (atoms, molecules, or ions) in one mole of a substance.

Question 17

In the reaction $$ N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g) $$, what is the correct mol-to-mol conversion factor between $$ NH_3$ $$ and $$ H_2$ $$?

Accepted Answer

$$ \frac{2 	ext{ mol } NH_3$}{3 	ext{ mol } H_2$} $$

Question 18

Which of the following is a correct mol-to-mass conversion factor for $$ H_2$ $$ gas?

Accepted Answer

$$ \frac{2.016 	ext{ g } H_2$}{1 	ext{ mol } H_2$} $$

Question 19

A chemical reaction produces $$ 3.00 $$ moles of $$ O_2$ . $$How many grams of $$ O_2$  is $$this? (Molar mass of $$ O_2$ = 32.00  g/$$mol)

Accepted Answer

$$ 96.00 	ext{ g} $$

Chapter 6: Chemical Composition – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards