Unit 9 mathematics of chemistry

AIM # 1 : How can we calculate gram formula mass? The atomic mass of an element is found in each element box on the Periodic Table The number of atoms of each element present in a compound is denoted by the subscripts on each element

Gram formula mass is the mass of the smallest unit of a compound from the sum of the atomic masses of all atoms present

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. 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 ____

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

Hydrates: crystals that contain attached water molecules To calculate the percentage of water in a hydrate, treat the water molecule as a single unit

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 = mass of that compound or element 1 mole = 6.02 x 1023 particles (atoms or molecules) 1 mole = 22.4 L Formula is on Table T

What is a mole? MOLE TRIANGLES

PRACTICE 1. 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 2. How many grams are equivalent to 2.8 moles of NaOH? Element # atoms X Mass # Multiplied result   Add them all up to get gfm

Aim # 4 How can we use mole relationships to solve stoichiometry problems? Like following a recipe Need a balanced chemical equation Use mole relationships The study of quantities of materials consumed and produced in chemical reactions

Practice …..like following a recipe Directions: Use the pancake recipe below in order to answer the following questions How much of the following starting materials do we need in order to make 14 pancakes? How many cups of pancakes mix would we need to use in order to make 28 pancakes? How many cups of pancake mix would we need to use in order to make 7 pancakes? 1 cup of milk + ____________________________ = 14 pancakes Are the units used for all 4 substances in the equation the same?

Formula:

If we had 5 moles of H2, how many moles of O2 are required?

If we have 23 grams of Na how many moles of H2 are produced?

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

AIM# 5: How can we calculate empirical and molecular formulas? convert % to grams divide each element by mass # 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

determine the gfm of the empirical formula MOLECULAR determine the gfm of the empirical formula Divide the given molecular mass by the gfm Might have to calculate empirical formula Given molecular mass Multiply your whole number result by the empirical formula to determine molecular formula

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