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SKILLS Project

SKILLS Project. Calculating Molar Masses. What are molar masses?. A molar mass is the weight, in grams, of a mole of any element or compound. Each element on the periodic table is assigned a molar mass. A compound’s molar mass is the sum of the masses of each element it contains.

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SKILLS Project

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  1. SKILLS Project Calculating Molar Masses

  2. What are molar masses? • A molar mass is the weight, in grams, of a mole of any element or compound. • Each element on the periodic table is assigned a molar mass. • A compound’s molar mass is the sum of the masses of each element it contains.

  3. Connections • Remember, a mole is 6.022e23 atoms/molecules of a substance. • So, the molar mass is a measurement of the total mass of a mole of these particles. • Due to the fact that the atoms of each element have different atomic masses, their molar masses are also different.

  4. To find molar mass: • List the elements in the compound. • Find the amount of each element. • Multiply each element by their unique molar masses. • Add up the individual totals to find the total molar mass of the compound.

  5. Example 1: Mass of Iron • A single element’s molar mass can be determined directly from the periodic table. • To do so, look at the atomic mass at the bottom of an element’s symbol. This number, in grams, is the molar mass of a single element. • We typically round the molar mass of an element to the nearest hundredth. So, 1 mol Fe = 55.85 g Fe. • The molar mass of Fe is 55.85 g/mol • 1 mol Fe = 55.85 g Fe

  6. Example 2: Fe2O3 • List the elements in the compound. Fe 2 55.85 g 2 111.70 g X = X = O 3 16.00 g 3 48.00 g = = X X 159.70 g/mol = 1 mol Fe2O3 = 159.70 g • Add up the individual totals to find the total molar mass of the compound. • Multiply each element by their unique molar masses • Find the amount of each element.

  7. Example 3: N2O4 • List the elements in the compound. N 2 14.01 g 2 28.02 g X = X = 4 16.00 g 4 64.00 g O = = X X 92.02 g/mol = 1 mol N2O4 = 92.02 g • Add up the individual totals to find the total molar mass of the compound. • Multiply each element by their unique molar masses • Find the amount of each element.

  8. Example 4: Na3PO4 Na 3 22.99 g 3 68.97 g • List the elements in the compound. X = X = 1 30.97 g 1 30.97 g P = = X X 4 16.00 g 4 64.00 g O = = X X 163.94 g/mol = 1 mol Na3PO4 = 163.94 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  9. Example 5: LiC2H3O2 Li 1 6.94 g 1 6.94 g X = X = • List the elements in the compound. 2 12.01 g 2 24.02 g C = = X X H 3 1.01 g 3 3.03 g = = X X O 2 16.00 g 2 32.00 g = = X X 65.99 g/mol = • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses 1 mol LiC2H3O2 = 65.99 g

  10. Note on Parentheses • Many compounds contain polyatomics listed in parentheses, such as: • Fe2(SO4)3 • The subscript outside the parenthesis will multiply all of the substances inside. • Fe x 2 • (S x 1) x 3 = S x 3 • (O x 4) x 3 = O x 12

  11. Example 6: Ir2(CO3)3 Ir 2 192.22 g 2 384.44 g • List the elements in the compound. X = X = 3 12.01 g 3 36.03 g C = = X X 9 16.00 g 9 144.00 g O = = X X 564.47 g/mol = 1 mol Ir2(CO3)3 = 564.47 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  12. Example 7: (NH4)3P N 4 14.01 g 4 56.04 g • List the elements in the compound. X = X = 12 1.01 g 12 12.12 g H = = X X 1 30.97 g 1 30.97 g P = = X X 99.13 g/mol = 1 mol (NH4)3P = 99.13 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  13. Example 8: (NH4)2Cr2O7 N 2 14.01 g 2 28.02 g X = X = • List the elements in the compound. 8 1.01 g 8 8.08 g H = = X X Cr 2 52.00 g 3 156.00 g = = X X O 7 16.00 g 7 112.00 g = = X X 304.10 g/mol = • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses 1 mol (NH4)2Cr2O7 = 304.10 g

  14. Example 9: AgCN Ag 1 107.87 g 1 107.87 g • List the elements in the compound. X = X = 1 12.01 g 1 12.01 g C = = X X N 1 14.01 g 1 14.01 g = = X X 133.89 g/mol = 1 mol AgCN = 133.89 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  15. Example 10: V(NO2)5 V 1 50.94 g 1 50.94 g • List the elements in the compound. X = X = N 5 14.01 g 5 70.05 g = = X X O 10 16.00 g 10 160.00 g = = X X 280.99 g/mol = 1 mol V(NO2)5 = 280.99 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  16. Example 11: Ba(OH)2 Ba 1 137.33 g 1 137.33 g • List the elements in the compound. X = X = O 2 16.00 g 2 32.00 g = = X X H 2 1.01 g 2 2.02 g = = X X 171.35 g/mol = 1 mol Ba(OH)2 = 171.35 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  17. Example 12: Au(NO3)4 Au 1 196.97 g 1 196.97 g • List the elements in the compound. X = X = N 4 14.01 g 4 56.04 g = = X X O 12 16.00 g 12 192.00 g = = X X 445.01 g/mol = 1 mol Au(NO3)4 = 445.01 g • Add up the individual totals to find the total molar mass of the compound. • Find the amount of each element. • Multiply each element by their unique molar masses

  18. Practice on Your Own: • Determine the molar masses of the following compounds: • CuCl2 – • O2 – • Se2N3 – • CCl4 – • Zr3(PO4)4 – 134.55 g/mol 32.00 g/mol 199.95 g/mol 153.81 g/mol 653.55 g/mol

  19. Practice on Your Own (2): • Determine the molar masses of the following compounds: • Pt(C2H3O2)7 – • SO2 – • ArF2 – • Co(ClO4)2 – • (NH4)2S2O3 – 608.43 g/mol 64.07 g/mol 77.95 g/mol 258.83 g/mol 148.24 g/mol

  20. Congratulations! • You have mastered the ability to find the molar mass of a substance based on its formula. • This skill is incredibly useful and allows you to find the conversion factors to turn measurements you take in lab, i.e. grams, into moles for chemical reactions.

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