Unit 9 mathematics of chemistry

AIM # 1 : How can we calculate gram formula mass and composition of compounds? What are the units we use to mass atoms? What is the mass of one atom of oxygen? _______________________________________ The atomic ____________ of an element is found in each element box on the__________________ Table Remember we don’t use grams for the units for massing atoms (because they are TOO small)

The number of atoms of each element present in a compound is denoted by the ____________________ on each element __________________________________ - one atom of an element that’s stable enough to stand on its own. They are not bonded to anything (very rare!) __________________________________________ elements whose atoms always travel in pairs, bonded to another atom of the same element What would the mass be of the one molecule of oxygen (O2)? ______________________

Calculating Formula Mass & Gram Formula Mass of Compounds: ____________________________________ : the mass of an atom, molecule or compound in atomic mass units (amu) Formula mass of a nitrogen atom is : _________________________________ ____________________________________ _: is the mass of one MOLE of an atom, molecule or compound in GRAMS (g)

GFM of K2CO3 Add them all up to get gfm Element # of atoms X Mass Multiplied result   Add them all up to get gfm

Calculate the gram formula mass of the following: 1. N2H2 2. H2SO4 3 Calculate the gram formula mass of the following: 1. N2H2 2. H2SO4 3. Ca Cl2 4. CuSO4 H20

AIM# 2 : What is meant by the percent composition of a compound? Percent Composition represents the composition as a percentage of each element compared with the total mass of the compound

% composition = mass of part mass of whole x 100  TABLE ____

___________________________: is a crystalline compound in which ions are attached to one or more water molecules. Water molecules are built into the chemical formula. Substance without water are anhydrates. To calculate the percentage of ______________________ in a hydrate, treat the water molecule as a ________________________

Practice What is the percentage, by mass, of O in Fe2O3? Element # atoms X Mass # Multiplied result   Add them all up to get gfm Fe O

Practice 2. What is the percentage, by mass, of O in CO2? Element # atoms X Mass # Multiplied result   Add them all up to get gfm l

What is the percentage, by mass, of water in sodium carbonate crystals, Na2CO3 10H2O?

AIM# 3: What is a mole? Mole is a way to express a quantity 1 mole of any compound or elements = gram formula mass of that compound or element 1 mole = 6.02 x 1023 atoms 1 mole = 22.4 L Example: 1 mole of carbon= 6.02 x 1023 atoms of carbon= 12.011 grams of carbon

MOLE TRIANGLES

PRACTICE A. How many moles are equivalent to 4.75 g of NaOH? Element # atoms X Mass # Multiplied result   Add them all up to get gfm

PRACTICE B. How many moles are in 39.0 grams of LiF? Element # atoms X Mass # Multiplied result   Add them all up to get gfm

C. What is the number of moles in Potassium chloride in 148.0 grams? D. How many moles are in 168 grams of KOH?   E. If you have 2.50 moles of H2SO4, what is the mass of your sample?

F. How many grams are in 2.8 moles of NaOH? G. What is the mass of 4.5 moles of KOH? H. What is the mass of 0.50 moles of CuSO4? I. What is the mass of 1.50 moles of nitrogen gas?

Aim # 4 How can we use mole relationships to solve stoichiometry problems? A chemical equation is basically the “recipe” for a reaction. The ___________________________ ___________________________________________________________ we need to make the recipe work. Reactants in an equation react in ratios to produce a specific amount of products.   Like following a recipe Need a balanced chemical equation Use mole relationships The study of quantities of materials consumed and produced in chemical reactions

If we wanted to make sugar cookies we would need:   3 eggs + 1 cup of flour + 2 cups of sugar  24 cookies If we wanted 48 cookies, how many eggs would we need? _______________________________ If we figured out the mass of the eggs, flour, sugar, it would equal the mass of the cookies. This illustrates the law of conservation of mass! 3E + 1F + 2S = 24C 200 g + 160 g + 240 g = 600 g If we had 10 eggs and plenty of sugar and flour, what would be the greatest amount of cookies you could make???

Formula:

Practice Using the following formula: N2 + 3H2  2NH3 1. How many moles of nitrogen gas would be needed to produce 10 moles of ammonia? 2. If 2.5 moles of N2 react completely, how many moles of NH3 are formed? 3. If 9 moles of NH3 are formed, how many moles of H2 reacted? 4. If 3.5 moles of NH3 are formed, how many moles of N2 reacted?

2 H2 + O2  2 H2O 5. If we had 5 moles of H2, how many moles of O2 are required?

  C3H8 + 5O2  3CO2 + 4H2O 6. If 12 moles of C3H8 react completely, how many moles of H20 are formed? 7. If 20 moles of CO2 are formed, how many moles of O2 reacted?

8. If we have 2 moles of N2 how many grams of H2 are needed?

AIM# 5: How can we calculate empirical and molecular formulas? Empirical formula: Molecular Formula: Example: N2O4 C5H12

convert % to grams (always assume 100 gram sample) EMPIRICAL convert % to grams (always assume 100 gram sample) divide each element by mass #. This converts grams to moles Divide each quotient by smallest value calculated. Round your results to nearest whole number Use whole #s to write empirical formula Sequence of elements in the question is the same as in the formula

A compound is composed of 50% Sulfur, 50% Oxygen; determine the empirical formula

2. A compound contains 24. 0 g C and 32. 0 g O 2. A compound contains 24.0 g C and 32.0 g O. What is the empirical formula? 3. 14.6 % C and 85.4 % Cl. Calculate empirical. 4. 67.1 % Zinc and the rest of the compound is Oxygen.

MOLECULAR Determine the empirical formula Determine the gfm of the empirical Divide the given molecular mass by the gfm Multiply your whole number result by the empirical formula to determine molecular formula

1. A compound is 80 % Carbon and 20 % Hydrogen by mass 1. A compound is 80 % Carbon and 20 % Hydrogen by mass. If the molecular formuals is 75.0 grams, what is the empirical formula? The molecular formula?

2. Upon analysis the empirical formula is determined to be CH2O 2. Upon analysis the empirical formula is determined to be CH2O. The mass of the compound is 180amu. Determine the molecular formula

3. A compound is 63. 6 % Nitrogen and 36. 4 % oxygen by mass 3. A compound is 63.6 % Nitrogen and 36.4 % oxygen by mass. Calculate its empirical formula. What is the molecular?