1. Mass Relationships in Chemical Reactions Chapter 3

2. Empirical Formula “Simplest formula” Indicates lowest whole-number ratio of atoms or ions in a compound Ionic compounds have empirical only For molecular compounds, need MM in addition to empirical formula to obtain molecular formula

3. Empirical Formula from Analyses Fig. 3.11

4. Sample Exercise 3.13, p 95 Ascorbic acid (Vitamin C) contains 40.92% C, 4.58% H, and 54.50% O by mass. (a) What is the empirical formula of ascorbic acid? (b) If the molar mass of ascorbic acid is 88 g/mol, what is the molecular formula of ascorbic acid?

5. Combustion Analysis Fig 3.12 Hydrocarbon + O 2 (g) → CO 2 (g) + H 2 O (l)

6. Sample Exercise 3.15, p 97 Isopropyl alcohol (IPA) is composed of C, H, and O. Combustion of 0.255 g of IPA produces 0.561 g CO 2 and 0.306 g H 2 O. Determine the empirical formula of IPA. Combust 0.255 g ethanol Collect 0.561 g CO 2 and 0.306 g H 2 O

7. 0.153 g C 0.0343 g H 0.255 g sample – (0.153 g C + 0.0342 g H) g CO 2 mol CO 2 mol Cg C g H 2 O mol H 2 Omol Hg H g of O = g of sample – (g of C + g of H) Logic: 0.068 g O

8. to obtain: C 2.98 H 7.91 O 1.00 Divide through by smallest: 0.0043 which readily gives: C 3 H 8 O the empirical formula

9. Empirical Formula of a Hydrate Hydrated copper (II) sulfate has the formula CuSO 4 · x H 2 O To find x, 1.023 g of the blue solid is heated in a crucible until its mass no longer decreases. The mass of the anhydrous, white CuSO 4 is 0.654 g. How many moles of water (x) are there per mole of CuSO 4 ?

10. Mass Changes in Chemical Reactions a.k.a. “Stoichiometry”

11. Methanol burns in air according to the equation 2CH 3 OH + 3O 2 2CO 2 + 4H 2 O If 209 g of methanol are used up in the combustion, what mass of water is produced? grams CH 3 OHmoles CH 3 OHmoles H 2 Ograms H 2 O molar mass CH 3 OH coefficients chemical equation molar mass H 2 O 209 g CH 3 OH 1 mol CH 3 OH 32.0 g CH 3 OH x 4 mol H 2 O 2 mol CH 3 OH x 18.0 g H 2 O 1 mol H 2 O x = 235 g H 2 O