1 / 17

Determining Chemical Formulas

Understand how to determine empirical formulas, calculate mole ratios, and find molecular formulas in chemistry with step-by-step examples and practice questions.

stobias
Télécharger la présentation

Determining Chemical Formulas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Determining Chemical Formulas 7-4

  2. Beaker Breaker • Name or write the following formulas: • AlN =___________________ • CO = ___________________ • Al2S3 =___________________ • Copper (II) Oxide =______________

  3. Empirical formula • formula that shows the smallest whole-number MOLE ratio of the different atoms in a compound • In ionic cmpds, the formula unit usually is the empirical formula

  4. What is the empirical formula of the following molecular formulas? • Ethyne, C2H2 • Benzene, C6H6 • Glucose, C6H12O6 • Acetic Acid

  5. Ethyne, C2H2 • CH • Benzene, C6H6 • CH • Glucose, C6H12O6 • CH2O • Acetic Acid • CH3COOH = C2H4O2 = CH2O

  6. Calculation of an empirical formula • Empirical formula: smallest whole-number MOLE ratio of the different atoms in a compound • ∴ 1)determine moles of each element • 2)determine the simplest whole # ratio of these moles

  7. What would the formula be of a cmpd that was composed of 2 mol hydrogen and 1 mol oxygen? • H:O mole ratio = 2:1 • ∴ H2O1…but always written H2O

  8. What would the formula be of a cmpd composed of 0.78 mol Al & 2.34 mol Br? • Mole ratio of Al: Br • = 0.78 : 2.34 • smallest whole # ratio????? • 0.78 mole Al = 1.0 Al 0.78 • 2.34 mol Br = 3.0 Br 0.78 • Al:Br = 1:3 AlBr3

  9. What is the empirical formula for a cmpd that contains 0.900 g calcium and 1.60 g chlorine? • Determine moles of Ca and Cl • Determine the simplest whole # mole ratio • 0.900 g Ca x 1 mol Ca = 0.0224 mole Ca 40.08 g Ca • 1.60 g Cl x 1 mol Cl = 0.0451 mol Cl 35.45 g Cl

  10. Simplest whole-# mole ratio? • 0.0224 mole Ca • 0.0451 mol Cl • 0.0224 mole Ca = 1.00 = 1 0.0224 mole • 0.0451 mol Cl = 2.01 = 2 0.0224 mole ∴ Ca:Cl = 1:2 CaCl2

  11. Beaker Breaker • A sample of indium chloride weighing 0.5000 g is found to contain 0.2404 g of chlorine. What is the empirical formula of the indium compound?

  12. Determine the empirical formula in a cmpd that is 40.0% C, 6.71% H, and 53.3% O. • Assume a 100.0 g sample. • 40.0 g C = 3.33 mol C • 6.71 g H = 6.64 mol H • 53.3 g O = 3.33 mol O • 3.33 mole C/3.33 = 1.00 = 1 • 6.64 mole H/3.33 = 1.99 = 2 • 3.33 mol O/3.33 = 1.00 = 1 • C:H:O = 1:2:1 CH2O

  13. If the empirical formula is CH2 and the molar mass is 42 g/mol, what is the molecular formula? • mass of empirical formula = 14 g/mol • mass of “real” formula = 42 g/mol • ∴ “real” is 42/14 or 3 times heavier! • C: H • 1: 2 (from empirical formula) • is really, 3( 1:2) = 3:6 C3H6 • (check: C3H6 does have a mass of 42 g/mol)

  14. If the molecular mass for the prev. problem (cmpd that is 40.0% C, 6.71% H, and 53.3% O)is 90 g/mol, determine the molecular formula. • The actual formula is how many times heavier than the empirical? • 3 times • ∴ molecular formula is 3xs bigger • 3 (C:H:O = 1:2:1) =3:6:3 C3H6O3

  15. Beaker Breaker • Write the symbol and oxidation # (incl +/-) for the following ions: • Calcium ____________________ • Chloride ___________________ • Oxide ____________________ • Sulfate ____________________

  16. Practice • Complete section review on page 233 #1-5

  17. Do Section Review p. 233 • Na2SO3 • Fe2S3 • K2CrO4 • N2O5 • N2O4

More Related