1. Chapter 7 Chemical Quantities
7.2 Molar Mass
Learning Goal Given the chemical formula of a substance, calculate its molar mass.
© 2014 Pearson Education, Inc.

2. the quantity in grams that equals the atomic mass of that element
Molar Mass
The molar mass is
the quantity in grams that equals the atomic mass of that element
the mass of one mole of an element or compound
the mass of × 1023 atoms of an element
the mass of × 1023 molecules or formula units
© 2014 Pearson Education, Inc.

3. Molar Mass of Carbon
© 2014 Pearson Education, Inc.

4. Molar Mass of a Compound
To determine the molar mass of a compound,
multiply the molar mass of each element by its subscript in the formula
add the results and round to 0.01 gram
Molar mass NH3
1 mol NH3 1 mol N =1(14.01 g N) = g N
3 mol H =3(1.01 g H) = 3.03 g H
Molar mass NH3 = g NH3
© 2014 Pearson Education, Inc.

5. Guide to Calculating Molar Mass
© 2014 Pearson Education, Inc.

6. Calculate the molar mass of lithium carbonate,
Learning Check
Calculate the molar mass of lithium carbonate,
Li2CO3, used to produce the red color in
fireworks.
© 2014 Pearson Education, Inc.

7. Calculate the molar mass of Li2CO3.
Solution
Calculate the molar mass of Li2CO3.
Step 1 Obtain the molar mass of each element.
From the periodic table:
© 2014 Pearson Education, Inc.

8. Calculate the molar mass of Li2CO3.
Solution
Calculate the molar mass of Li2CO3.
Step 2 Multiply each molar mass by the moles (subscript) in the formula.
2 mol Li × = g Li
1 mol C × = g C
3 mol O × = g O
© 2014 Pearson Education, Inc.

9. Calculate the molar mass of Li2CO3.
Solution
Calculate the molar mass of Li2CO3.
Step 3 Calculate the molar mass by adding the masses of the elements.
2 mol Li = g Li
1 mol C = g C
3 mol O = g O
Molar mass Li2CO3 = g Li2CO3
© 2014 Pearson Education, Inc.

10. One-Mol Quantities
One-mol samples: sulfur, S (32.07 g); iron, Fe (55.85 g); salt, NaCl (58.44 g); potassium dichromate, K2Cr2O7 (294.2 g); and sucrose, C12H22O11 (342.3 g).
© 2014 Pearson Education, Inc.

11. Molar Mass of Elements, Compounds
© 2014 Pearson Education, Inc.

12. Calculate the molar mass of potassium chloride, KCl.
Learning Check
Calculate the molar mass of potassium chloride,
KCl.
© 2014 Pearson Education, Inc.

13. Calculate the molar mass of potassium chloride, KCl.
Solution
Calculate the molar mass of potassium chloride,
KCl.
Step 1 Obtain the molar mass of each element.
© 2014 Pearson Education, Inc.

14. Calculate the molar mass of potassium chloride, KCl.
Solution
Calculate the molar mass of potassium chloride, KCl.
Step 2 Multiply each molar mass by the moles (subscript) in the formula.
1 mol K x = g K
1 mol Cl x = g C
© 2014 Pearson Education, Inc.

15. Calculate the molar mass of potassium chloride, KCl.
Solution
Calculate the molar mass of potassium chloride, KCl.
Step 3 Calculate the molar mass by adding the masses of the elements.
1 mol K = g K
1 mol Cl = g Cl
Molar mass KCl = g KCl
© 2014 Pearson Education, Inc.