10.4-EMPERICAL FORMULA Determiningchemicalformula.pptx

10.4-EMPERICAL FORMULA Determiningchemicalformula.pptx

1. Determining chemical formula Chapter 10 – section 4

2. Determine a compound’s empirical formula from its percentage composition. Determine the molecular formula or formula unit of a compound from its empirical formula and its formula mass. Calculate percentage composition of a compound from its molecular formula or formula unit.

3. Air composition

4. ROUND ROBIN What is the composition of atmosphere? What are the causes of air pollution in UAE?

5. Percentage composition The percentage composition is the percentage by mass of each element in a compound. Percentage Composition of Iron Oxides

6. An empirical formula is a chemical formula that shows the simplest ratio for the relative numbers and kinds of atoms in a compound. An actual formula shows the actual ratio of elements or ions in a single unit of a compound. For example, the empirical formula for ammonium nitrate is NH 2 O, while the actual formula is NH 4 NO 2 .

7. Determining Empirical Formulas You can use the percentage composition for a compound to determine its empirical formula. Convert the percentage of each element to g. Convert from g to mol using the molar mass of each element as a conversion factor. Compare these amounts in mol to find the simplest whole-number ratio among the elements.

8. Sample Problem Chemical analysis of a liquid shows that it is 60.0% C, 13.4% H, and 26.6% O by mass. Calculate the empirical formula of this substance. Assume that you have a 100.0 g sample, and convert the percentages to grams. for C: 60.0%  100.0 g = 60.0 g C for H: 13.4%  100.0 g = 13.4 g H for O: 26.6%  100.0 g = 26.6 g O

9. Convert the mass of each element into the amount in moles, using the reciprocal of the molar mass.

10. The formula can be written as C5H13.3O1.66, but you divide by the smallest subscript to get whole numbers. The empirical formula is C 3 H 8 O.

11. Solve problems  2, 3, 4, and 5 Worksheet

12. Molecular Formulas Are Multiples of Empirical Formulas The formula for an ionic compound shows the simplest whole-number ratio of the large numbers of ions in a crystal of the compound. A molecular formula is a whole-number multiple of the empirical formula. The molar mass of any compound is equal to the molar mass of the empirical formula times a whole number, n .

13. Determining a Molecular Formula from an Empirical Formula Sample Problem A: The empirical formula for a compound is P 2 O 5 . Its experimental molar mass is 284 g/mol. Determine the molecular formula of the compound. Find the molar mass of the empirical formula P 2 O 5 . 2  molar mass of P = 61.94 g/ mol + 5  molar mass of O = 80.00 g/ mol molar mass of P 2 O 5 = 141.94 g/ mol

14. n (empirical formula) = 2 (P 2 O 5 ) = P 4 O 10

15. Solve problems on previously worksheet

16. The empirical formula of the anticancer drug altretamine is C 3 H 6 N 2 . The experimental molar mass is 210 g/mol. What is its molecular formula?

17. Chemical Formulas Can Give Percentage Composition If you know the chemical formula of any compound, then you can calculate the percentage composition. From the subscripts, determine the mass contributed by each element and add these to get molar mass. Divide the mass of each element by the molar mass. Multiply by 100 to find the percentage composition of that element.

18. CO and CO2 are both made up of C and O, but they have different percentage compositions.

19. Sample Problem A: Calculate the percentage composition of copper(I) sulfide, Cu 2 S, a copper ore called chalcocite. Find the molar mass of Cu 2 S. 2 mol  63.55 g Cu/ mol = 127.10 g Cu + 1 mol  32.07 g S/ mol = 32.07 g S molar mass of Cu 2 S = 159.17 g/ mol 79.852% Cu   × 100 =

20. 20.15% S

21. Answer questions on previously worksheet