2. IIIIIIIV Chapter 10 – Chemical Quantities

3. What is the Mole? n A unit of measurement used in chemistry. n A counting number like – a dozen eggs, a ream of paper, a bushel of apples, etc. n A mole describes an amount of matter.

4. Definition: n A mole of any element is defined as the number of atoms of that element equal to the number of atoms in exactly 12.0 grams of carbon-12.

5. Atomic Mass n Mass of a single atom  10 -23 grams n Atomic Mass Unit (amu) is used to describe the atomic mass of an atom. n A scale was devised to express the mass of all the different atoms. n Based on the mass of an atom relative to carbon-12.

6. n Atomic Masses are listed in the periodic table.

7. n 1 atom of 12 C has a mass of 12.01 amu n 1 mole of 12 C has a mass of 12.01 grams What it means:

8. n 1 atom of 35 Cl has a mass of 35.45 amu n 1 mole of 35 Cl has a mass of 35.45 grams What it means:

9. Formula Mass n Is calculated using the atomic mass of each element in the compound, times how many atoms of each element are in the compound.

10. Example: n Find the formula mass of H 2 O H = 2 x 1.0 = 2.0 grams O = 1 x 16.0 = 16.0 grams 18.0 grams/mole

11. Example: n Find the formula mass of NaOH Na = 1 x 23.0 = 23.0 grams O = 1 x 16.0 = 16.0 grams 40.0 grams/mole H = 1 x 1.0 = 1.0 grams

12. The Atomic Mass or Formula Mass n Tells the mass in grams of 1 mole of a substance

13. n There are 6.02 x 10 23 objects in one mole. n 602,000,000,000,000,000,000,000

14. n 1 mole of hockey pucks would equal the mass of the moon! A. What is the Mole? n 1 mole of pennies would cover the Earth 1/4 mile deep! n 1 mole of basketballs would fill a bag the size of the earth!

15. A mole of sugar A mole of water A mole of copper

16. Example: 16.0 g of oxygen 1 mole of oxygen 6.02 x 10 23 atoms of oxygen = =

17. Example: 18.0 g of water 1 mole of water 6.02 x 10 23 molecules of water = =

18. Example: 40.0 g of NaOH dissolved in water 1 mole of Na + ions and 1 mole of OH - ions 6.02 x 10 23 Na + ions and 6.02 x 10 23 OH - ions = =

19. Molar Mass n Mass in grams of 1 mole of a substance.

20. Molar Mass Examples n water n sodium chloride H2OH2O  2(1.01) + 16.00 = 18.02 g/mol  NaCl  22.99 + 35.45 = 58.44 g/mol

21. Molar Mass Examples n sodium bicarbonate n sucrose  NaHCO 3  22.99 + 1.01 + 12.01 + 3(16.00) = 84.01 g/mol  C 12 H 22 O 11  12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol

22. Molar Conversions molar mass (g/mol) MASS IN GRAMS MOLES NUMBER OF PARTICLES 6.02  10 23 (particles/mol) ÷ x x ÷

23. Molar Conversion Examples n How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C

24. Molar Conversion Examples n How many molecules are in 2.50 moles of C 12 H 22 O 11 ? 2.50 mol 6.02  10 23 molecules 1 mol = 1.51  10 24 molecules C 12 H 22 O 11

25. Molar Conversion Examples n Find the mass of 2.1  10 24 molecules of NaHCO 3. 2.1  10 24 molecules 1 mol 6.02  10 23 molecules = 293 g NaHCO 3 84.01 g 1 mol

26. IIIIIIIV Suggested Reading: Pages 305 - 313 Chapter 10 – % Composition, Empirical and Molecular Formulas

27. Percentage Composition n the percentage by mass of each element in a compound

28.  100 = Percentage Composition %Cu = 128g Cu 160 g Cu 2 S  100 = %S = 32 g S 160 g Cu 2 S 80% Cu 20% S n Find the % composition of Cu 2 S.

29. %Fe = 28 g 36 g  100 = 78% Fe %O = 8.0 g 36 g  100 = 22% O n Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. Percentage Composition

30. n How many grams of copper are in a 38.0-gram sample of Cu 2 S? (38.0 g Cu 2 S)(0.80) = 30.4 g Cu Cu 2 S is 80% Cu Percentage Composition

31.  100 = %H 2 O = 36 g 146 g 25% H 2 O n Find the mass percentage of water in calcium chloride dihydrate, CaCl 2 2H 2 O? Percentage Composition

32. Empirical Formula C2H6C2H6 CH 3 reduce subscripts n Smallest whole number ratio of atoms in a compound

33. Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

34. Empirical Formula Song (to help you remember steps) 1. Percent to Mass 2. Mass to Mole 3. Divide by Small 4. Multiply ‘til Whole

35. Empirical Formula n Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14 g = 1.85 mol N 74.1 g 1 mol 16 g = 4.63 mol O 1.85 mol = 1 N = 2.5 O

36. Empirical Formula N 1 O 2.5 Need to make the subscripts whole numbers  multiply by 2 N2O5N2O5

37. Molecular Formula n “True Formula” - the actual number of atoms in a compound CH 3 C2H6C2H6 empirical formula molecular formula ?

38. Molecular Formula 1. Find the empirical formula. 2. Find the empirical formula mass. 3. Divide the molecular mass by the empirical mass. 4. Multiply each subscript by the answer from step 3.

39. Molecular Formula n The empirical formula for ethylene is CH 2. Find the molecular formula if the molecular mass is 28.1 g/mol? 28.1 g/mol 14 g/mol = 2.00 empirical mass = 14.03 g/mol (CH 2 ) 2  C 2 H 4