1. Mole Relationships

2. By definition: 1 atom 12 C “weighs” 12 amu Atomic mass is the mass of an atom in atomic mass units (amu) The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.00 grams of 12 C

3. Molar mass is the mass of 1 mole of in grams eggs shoes marbles atoms 1 mole 12 C atoms = 6.022 x 10 23 atoms = 12.00 g 1 12 C atom = 12.00 amu 1 mole 12 C atoms = g 12 C 1 mole lithium atoms = g of Li For any element atomic mass (amu) = molar mass (grams)

5. One Mole of: C S Cu Fe Hg

6. Do You Understand Molar Mass? How many atoms are in 0.551 g of potassium (K) ?

7. Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO 2 1S32.07 amu 2O+ 2 x 16.00 amu SO 2 64.07 amu For any molecule molecular mass (amu) = molar mass (grams)

8. Do You Understand Molecular Mass? How many H atoms are in 72.5 g of C 3 H 8 O ?

9. Percent composition of an element in a compound = n x molar mass of element molar mass of compound x 100% n is the number of moles of the element in 1 mole of the compound C2H6OC2H6O

10. Do You Understand Percent composition ? What is the percent composition of each element in C 3 H 8 O ?

11. Types of Formulas Empirical FormulaEmpirical Formula The formula of a compound that expresses the smallest whole number ratio of the atoms present. Ionic formula are always empirical formula Molecular FormulaMolecular Formula The formula that states the actual number of each kind of atom found in one molecule of the compound.

12. To obtain an Empirical Formula 1.Determine the mass in grams of each element present, if necessary. 2.Calculate the number of moles of each element. 3.Divide each by the smallest number of moles to obtain the simplest whole number ratio. 4.If whole numbers are not obtained * in step 3), multiply through by the smallest number that will give all whole numbers * Be careful! Do not round off numbers prematurely

13. To obtain an Empirical Formula

14. A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine an empirical formula for this substance.

15. To obtain a Molecular Formula

16. Calculation of the Molecular Formula A compound has an empirical formula of NO 2. The colourless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?

17. Empirical Formula from % Composition A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance?

18. Molecular Formula from % Composition A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the molecular formula of the substance if the molecular mass is 151.2 g/mol?

19. Combustion Analysis Many times it is difficult to determine the mass of individual elements. We can use combustion analysis of organic elements to determine the empirical formula for these compounds 1.Find total mass combusted 2.Find mass water using water absorption 3.Find mass carbon dioxide through CO 2 absorption 4.Find remaining mass of other elements if needed.

20. Combust 11.5 g ethanol Collect 22.0 g CO 2 and 13.5 g H 2 O

21. Combust 11.5 g ethanol Collect 22.0 g CO 2 and 13.5 g H 2 O If molar mass was found to be 46 g/mole what is the molecular formula?

22. Do You Understand Combustion analysis? What is the empirical formula if 31.81 g CO 2 and 11.39 g H 2 O were collected from a 15.0 g sample of an organic molecule containing carbon hydrogen and nitrogen?