Larry Emme Chemeketa Community College

1. Quantitative Composition Chapter 7 Larry Emme Chemeketa Community College

2. The Mole

3. The mass of a single atom is too small to measure on a balance. mass of hydrogen atom = 1.673 x 10-24 g

4. This is an infinitesimal mass 1.673 x 10-24 g

5. MOLE • Chemists require a unit for counting which can express large numbers of atoms using simple numbers. • Chemists have chosen a unit for counting atoms. • That unit is the

6. 1 mole = 6.02 x 1023 objects

7. 6.02 x 1023 is a very LARGE number

8. 6.02 x 1023 is Avogadro’s Number number

9. Amadeo (Amedeo) Avogadro

10. If 10,000 people started to count Avogadro’s number and counted at the rate of 100 numbers per minute each minute of the day, it would take over 1 trillion years to count the total number.

11. 1 mole of any element contains 6.02 x 1023 particles of that substance.

12. The atomic weight in grams of any element23 contains 1 mole of atoms.

13. This is the same number of particles6.02 x 1023as there are in exactly 12 grams of

14. Examples

15. H SpeciesQuantity Number of H atoms 1 mole 6.02 x 1023

16. H2 SpeciesQuantity Number of H2molecules 1 mole 6.02 x 1023

17. Na SpeciesQuantity Number of Na atoms 1 mole 6.02 x 1023

18. Fe SpeciesQuantity Number of Fe atoms 1 mole 6.02 x 1023

19. C6H6 SpeciesQuantity Number of C6H6molecules 1 mole 6.02 x 1023

20. 1 mol of atoms = 6.02 x 1023 atoms 1 mol of molecules = 6.02 x 1023 molecules 1 mol of ions = 6.02 x 1023 ions

21. The mole weight of an element is its atomic weight in grams. • It contains 6.02 x 1023 atoms (Avogadro’s number) of the element.

23. Problems

24. Convert To Moles!

25. How many moles of iron does 25.0 g of iron represent? Conversion sequence: grams Fe → moles Fe Atomic weight iron = 55.85 Set up the calculation using a conversion factor between moles and grams.

26. How many iron atoms are contained in 40.0 grams of iron? Atomic weight iron = 55.85 Conversion sequence: grams Fe → atoms Fe Set up the calculation using a conversion factor between atoms and grams.

27. What is the mass of 3.01 x 1023 atoms of sodium (Na)? Mole weight Na = 22.99 g Conversion sequence: atoms Na → grams Na Set up the calculation using a conversion factor between grams and atoms.

28. What is the mass of 0.365 moles of tin? Atomic weight tin = 118.7 Conversion sequence: moles Sn → grams Sn Set up the calculation using a conversion factor between grams and atoms.

29. How many oxygen atoms are present in 2.00 mol of oxygen molecules? Two conversion factors are needed: Conversion sequence: moles O2→ molecules O2 → atoms O

30. Mole Weight of Compounds

31. The mole weight of a compound can be determined by adding the mole weights of all of the atoms in its formula.

32. Calculate the mole weight of C2H6O. 2 C = 2(12.01 g) = 24.02 g 6 H = 6(1.01 g) = 6.06 g 1 O = 1(16.00 g) = 16.00 g 46.08 g

33. Calculate the mole weight of LiClO4. 1 Li = 1(6.94 g) = 6.94 g 1 Cl = 1(35.45 g) = 35.45 g 4 O = 4(16.00 g) = 64.00 g 106.39 g

34. Calculate the mole weight of (NH4)3PO4 . 3 N = 3(14.01 g) = 42.03 g 12 H = 12(1.01 g) = 12.12 g 1 P = 1(30.97 g) = 30.97 g 4 O = 4(16.00 g) = 64.00 g 149.12 g

35. Solids that contain water as part of their crystalline structure are known as hydrates. Water in a hydrate is known as water of hydration or water of crystallization.

36. CoCl2 6H2O Formulas of hydrates are written by first writing the formula for the anhydrous compound and then adding a dot followed by the number of water molecules present.

37. Calculate the mole weight of NaC2H3O2 · 3 H2O 1 Na = 1(22.99 g) = 22.99 g 2 C = 2(12.01 g) = 24.02 g 9 H = 9(1.01 g) = 9.09 g 5 O = 5(16.00 g) = 80.00 g 136.10 g

38. Avogadro’s Number of Particles 6.02 x 1023 Particles 1 MOLE Mole Weight

39. Avogadro’s Number ofCa atoms 6.02 x 1023 Ca atoms 1 MOLE Ca 40.078 g Ca

40. Avogadro’s Number ofH2O molecules 6.02 x 1023 H2O molecules 1 MOLE H2O 18.02 g H2O

41. These relationships are present when hydrogen combines with chlorine.

42. In dealing with diatomic elements (H2, O2, N2, F2, Cl2, Br2, and I2), distinguish between one mole of atoms and one mole of molecules.

43. Calculate the mole weight of 1 mole of H atoms. 1 H = 1(1.01 g) = 1.01 g Calculate the mole weight of 1 mole of H2molecules. 2 H = 2(1.01 g) = 2.02 g

44. Problems

45. How many moles of benzene, C6H6, are present in 390.0 grams of benzene? The mole weight of C6H6 is 78.12 g. Conversion sequence: grams C6H6→ moles C6H6

46. How many grams of (NH4)3PO4 are contained in 2.52 moles of (NH4)3PO4? The mole weight of (NH4)3PO4 is 149.12 g. Conversion sequence: moles (NH4)3PO4→ grams (NH4)3PO4

47. 56.04 g of N2 contains how many N2 molecules? The mole weight of N2 is 28.02 g. Conversion sequence: g N2 → moles N2→ molecules N2 Use the conversion factors

48. 56.04 g of N2 contains how many N atoms? The mole weight of N2 is 28.02 g. Conversion sequence: g N2 → moles N2→ molecules N2 → atoms N Use the conversion factors

49. Percent Compositionof Compounds

50. H2O 11.19% H by mass 88.79% O by mass Percent composition of a compound is the mass percent of each element in the compound.