The document discusses empirical formulas, molecular formulas, and percent composition. It provides examples of compounds with the same empirical formula but different molecular formulas, like ethyne and styrene which both have an empirical formula of CH but different molecular formulas. It also gives examples of compounds like methanal, ethanoic acid, and glucose that have the same empirical formula of CH2O.

1. Bellwork- oxygen tank 1)A small portable oxygen tank holds 164 liters of oxygen gas. How many moles does it contain? 2)How many O 2 molecules does the tank contain? 3)How many Oxygen atoms?

2. The percent by mass or Mass percent of an element is the number of grams of an element in a compound, divided by the molar mass of the compound, and then multiplied by 100%. Percent composition gives the mass percent of each element in a compound.

13. The empirical formula of a compound shows the smallest whole-number ratio of the atoms in the compound.

14. Ethyne (C 2 H 2 ) is a gas used in welder’s torches. Styrene (C 8 H 8 ) is used in making polystyrene. These two compounds of carbon have the same empirical formula (CH) but different molecular formulas.

15. 10.11 STEP 1- assume a 100g sample (percentages become grams) STEP 2- convert grams to moles 25.9g N 74.1g O = 1.85 moles N = 4.63 moles O STEP 3- divide all quantities by the lowest # _________ = 1 1.85 moles _________ = 2.5 1.85 moles 1mole N 14g N x ------------- 1mole O 16g O x ------------- x2 =2 x2 =5 N 2 O 5

17. The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula.

18. Methanal, ethanoic acid, and glucose all have the same empirical formula—CH 2 O.

25. Which of the following is NOT an empirical formula? NO 2 H 2 N CH C 3 H 6