# Chemistry Hl Formulas Chapter

Topics: Oxygen, Molecule, Hydrogen Pages: 4 (855 words) Published: October 1, 2012
Formulas
Chapter: 1
Section: 2
* The empirical formula: the formula that gives the simplest ratio of the number of atoms in the compound. Determination of the empirical formula:
1. Find the mass in grams of each element.
2. Find the number of moles.
3. Find the simplest ratio of moles.

Question
1. Mass of elements in g.
2. Number of moles of each element.
3. Simple ratio of elements.
Practice problems
* A 2.765 g sample of lead oxide was heated in a stream of hydrogen gas and completely converted to elemental lead with a mass of 2.401g. What is the empirical formula of the oxide? Mass of oxygen = 2.765 – 2.401 = 0.364 g

Number of moles of oxygen = 0.364/16 = 0.02275
Number of moles of lead = 2.401/20719 = 0.011588
Divide by 0.011588
O = 0.02275/0.011588 = 1.96 approximately 2
Pb = 0.011588 / 0.011588 = 1
Empirical formula is PbO2
A compound contains sodium, Sulfur and oxygen has a mass of 15.8 g, if it contains 4.6 g Na, 6.4 g S find the empirical formula (Na = 23, S = 32, O = 16)
Mass of oxygen = 15.8 – (4.6 + 6.4) = 4.8 g
Number of moles of oxygen = 4.8 / 16 = 0.3
Number of moles of sodium = 4.6 / 23 = 0.2
Number of moles of sulfur = 6.4 / 32 =
* Deduce the empirical formula of a hydrocarbon that contains 85.7 % by mass of carbon.

* Elemental analysis of a pure compound isolated from tea leaves gave the following results: 49.48 % C, 5.19% H, 28.85% N, 16.48% O. What is the empirical formula of the compound? ( C = 12, H = 1, N = 14, O = 16 ).

* An organic compound is composed 40% C and 6.7 % H by mass dense its empirical formula. ( C = 12, H = 1, O = 16 ) | C| H| O|
%| 40| 67| 100 - (40+67)|
Moles| 40/12 = 3.33| 67/1 = 67| 53.3/16 = 3.33|
Simple Ratio| 3.33/3.33 = 1| 6.7/3.33 = 2| 3.33/3.33 = 1|

CH2O
* What is the empirical formula of a purified drug sample that is 74.27 % C, 7.79 % H, 12.99 % N, and 4.95 % O? * ( C = 12, H = 1, N = 14, O = 16 )
| C| H| N|...

Please join StudyMode to read the full document