1 / 15

Aim: What is the difference between empirical and molecular formulas?

Aim: What is the difference between empirical and molecular formulas?. Do Now: Complete Worksheet Homework: Castle Learning #3, test Friday, Quiz Wednesday. VIII. Percent Composition, Molecular and Empirical Formulas.

walter-hyde
Download Presentation

Aim: What is the difference between empirical and molecular 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. Aim: What is the difference between empirical and molecular formulas? Do Now: Complete Worksheet Homework: Castle Learning #3, test Friday, Quiz Wednesday

  2. VIII. Percent Composition, Molecular and Empirical Formulas a) Percent Composition: the composition of a compound in terms of the percentage of each component present with respect to the whole. Ex #1: What is the percent composition by mass of the elements in sodium sulfate? • Find the formula of sodium sulfate. • Find the molar mass of sodium sulfate. • Using the formula for % composition by mass (reference table T), calculate the % composition of each element in the compound.

  3. Sodium Sulfate - Na2SO4 Na2SO4 Na = 2 X 23 = 46 S = 1 X 32 = 32 O = 4 X 16 = 64 • Molar Mass = 142 g/mol • % composition = part/whole X 100 Na = 46/142 X 100 = 32.4% S = 32/142 X 100 = 22.5% O = 64/142 X 100 = 45.1% 100%

  4. Ex #2: What is the percent composition by mass of the elements in Potassium permanganate? Ex #3: What is the percent composition by mass of the water in Copper (II) sulfate pentahydrate?

  5. b) Types of Formulas • Molecular Formulas • Represents the type and number of elements in a covalent compound. • The subscripts do not need to be reduced in a molecular formula. Ex:C2H4Ethene C6H12O6 Glucose

  6. 2. Empirical Formulas • Represents the lowest whole number ratio of atoms in a compound. • For ionic compounds, the formula is always empirical. This is due to the fact that one must reduce the subscripts in an ionic compound to the lowest whole number ratio. • For covalent compounds (molecules), reducing its molecular formula to an empirical formula only shows the ratio of elements within the compound. Ex: C6H12O6Molecular Formula C1H2O1Empirical Formula Ratio: C:H:O = 1:2:1

  7. c) Determining empirical formulas from percent composition • One can determine the chemical formula for a substance if given the percent composition of its elements. Ex: What is the empirical formula of a compound that consists of 58.80% barium, 13.75% sulfur, and 27.45% oxygen by mass? 1. Convert the percentages to grams. Ba 58.80% 58.80g S 13.75% 13.75g O 27.45% 27.45g

  8. 2. Convert from Mass to Moles Ba 137g = 58.80g = 0.43 mol 1 mol x mol S 32g = 13.75g = 0.43 mol 1 mol x mol O 16g = 27.45g = 1.71 mol 1 mol x mol

  9. 3. Simplify the mole ratios to the lowest whole number Ba = 0.43/0.43 = 1 S = 0.43/0.43 = 1 O = 1.71/0.43 = 4 4. The simplified ratio of elements is equal to the subscripts of the atoms within the compounds. Ba1S1O4 or BaSO4

  10. Practice: Given the following % compositions, determine the formulas for the following compounds. • 27.3 % carbon; 72.7 % oxygen • 30.43 % nitrogen; 69.57% oxygen

  11. c) 37.6% carbon; 12.5% hydrogen; 49.9% oxygen d) 32.4 % sodium; 22.5% sulfur; 45.1% oxygen

  12. c) Determining molecular formulas from percent composition KEY IDEA: The procedures for determining the molecular formula of a compound (given its elements % composition) is the same as finding its empirical formula with one exception. • YOU MUST DETERMINE THE EMPIRICAL MASS OF THE COMPOUND. • YOU MUST DIVIDE THE MOLECULAR MASS BY THE EMPIRICAL MASS TO DETERMINE THE ACTUAL NUMBER OF MOLES OF ATOMS WITHIN THE COMPOUND.

  13. Ex #1: In analyzing 30g of a compound, it was determined to consist of 80% carbon and 20% hydrogen by mass. • Determine the compound’s empirical and molecular formulas. 1. Convert percentages to grams 80% C = 80g C 20% H = 20g H 2. Convert Mass to Moles 80g C/12g per mole = 6.66 moles 20g H/1g per mole = 20 moles 3. Simplify mole ratios C = 6.66/6.66 = 1 H = 20/6.66 = 3

  14. 4. The mole ratios represent the subscripts for the empirical formula C1H3 5. Calculate the empirical mass C = 1 X 12 = 12 H = 3 X 1 = 3 Empirical Mass 15g/mole 6. Divide the molecular mass (given) by the empirical mass to find the formula unit Molecular Mass = 30 = 2 Empirical Mass 15

  15. 7. Distribute the formula unit 2 C1H3 = C2H6 C2H6 MOLECULAR FORMULA =

More Related