3.   I can determine the percent composition for each element in a compound or sample.

4.   Note Expectations:  Cell phones and electronics are not in use.  You are taking the notes.  You are helping the people at your table to answer the questions.  You are prepared to answer the questions.

5.   What is a percent?  On the mole test, you earned 25 out of 33. What percent did you get on the test?  How do you calculate a percent?

6.   What does the formula C 6 H 12 O 6 tell us?  How do you find the mass of a compound?

7.   The formula for a compound indicates the number and kinds of atoms in a representative particle of the compound.  The mass of a compound is made up of smaller masses of different elements. Formulas

8.   What is the percent of hydrogen and the percent of oxygen in H 2 O? Show how you think you would solve this problem. Work as a Table

9.   The percent composition of a compound tells you the percent mass made up by each element in the compound.  The percent composition can be determined by taking the mass of individual elements and dividing by the total mass. Percent Composition

10.   Then, you multiply by 100 to get the percent composition. Percent Composition

11.   What is the percent composition of H and O in H 2 O 2 ? Example

12.   What is the percent composition of N and O if 22.6g of N and 54.4 g of O are present in a 77.0 gram sample?

13.   Once you have found all of the percents, they should add up to 100%, or close to it based on rounding. Check your work!

14.  1. What is a percent? 2. How do you calculate a percent? You can answer this with an example. 3. What does a formula tell you? 4. What does percent composition tell you? 5. What is the total mass of a compound made of? Review Questions

15.  Empirical Formulas

16.   I can define empirical formula.  I can determine the empirical formula if given the elements in the formula.

17.   Note Expectations:  Cell phones and electronics are not in use.  You are taking the notes.  You are helping the people at your table to answer the questions.  You are prepared to answer the questions.

18.   What is a ratio?  What is the ratio of hydrogen to carbon in C 6 H 12 O 6 ?

19.   A formula that gives the simplest whole number ratio of the atoms of the elements is called an empirical formula. Empirical Formula

20.   What would the simplest ratio of C 6 H 12 O 6 be?

21.   The molecular formula for peroxide is H 2 O 2.  The empirical formula for peroxide is HO.  The empirical formula simply tells you the ratio of atoms, in this case 1:1. Formulas

22.   To determine the empirical formula based on % composition, you assume 100g.  This will make the math easier.  Next, you convert each of the masses to moles using the molar mass of the element. Procedure

23.   How do you convert mass to moles?  Where does the mass of an element come from? Review Question

24.   You divide each element by the smallest number of moles.  Round your answers to the nearest whole number.  These then become the subscripts for each element in the formula.  This is your ratio for the empirical formula. Procedure

25.   A compound has a percent composition of 80% C and 20% H, what is its empirical formula? Example

26.   If you are given grams instead of percents, you can start by converting to moles.

27.   A compound was found to have 13.5g Ca, 10.8g O, and 0.675g H, what is its empirical formula? Example

28.  1.What is a ratio? 2.What is an empirical formula? 3.Summarize the steps required to calculate an empirical formula. Review Questions

29.  Calculating Molecular Formulas

30.   I can define molecular formula.  I can determine the molecular formula if given the proper information.

31.   Note Expectations:  Cell phones and electronics are not in use.  You are taking the notes.  You are helping the people at your table to answer the questions.  You are prepared to answer the questions.

32.   Is the empirical formula the actual formula? How do you think it compares?  Could the empirical formula be the actual formula? Why or why not?

33.   The molecular formula can be the same as the empirical formula.  However, most of the time it is a whole number multiple of the empirical formula. Molecular Formulas

34.   You can determine the molecular formula of a compound if you know its molar mass.  First, you find the mass of the empirical formula. Procedure

35.   This is called the empirical formula mass or efm.  Then you take the known molar mass and divide by the efm. Procedure

36.   This gives you the number of empirical formula units in one molecule of the compound.  Take the number you got and round to the nearest whole number. Procedure

37.   Then, multiply all of the subscripts in the formula by that number.  This will give you the molecular formula. Procedure

38.   Calculate the molecular formula of the compound whose molar mass is 60.0g and empirical formula is CH 4 N. Example

39.   What is a molecular formula?  How is the molecular formula related to the empirical formula?  Summarize the steps to calculate the molecular formula. Review Questions