EMPIRICAL FORMULAS are the simplest formula of a compound. - show only the simplest ratios, NOT the actual atoms.
MOLECULAR FORMULAS give the actual number of atoms.
Empirical Formulas: - to determine the empirical formula, we need to know the ratio of each element. - to determine the ratio fill in the table below for each problem.
**MEMORIZE (make sure you know this table by heart<3)
example: A sample of an unknown compound is found to contain 8.4 of 'C', 2.1g of 'H' and 5.6g of 'O'. Determine the empirical formula.
Molecular Formulas:
- if you know an empirical formula to find the molecular formula you need the molar mass.
example: The empirical formula for a substance is CH2O and its molar mass is 60.0g/mol. Determine the molecular formula.
Today we learned about Mole to Mole conversions.
Basically, it is coefficients in balanced equations which tells us the number of moles reacted or produced!
3x + Y ---> 2Z *WHAT YOU NEED OVER WHAT YOU HAVE
Some examples:
If 0.16 mol of methane are consumed in a combustion reaction how many moles of CO2 are produced? Let's start off by what we are given!
The formula for methane is CH4. We know that Combustion reactions produce Carbon Dioxide (CO2) and water (H2O)
So it will look like this: CH4 ---> Co2 + H2O But we aren't finished here because since theres oxygen atoms on the right side, we must have oxygen atoms on the left side of the equation as well. Remember that Oxygen is diatomic so our new equation will look like this:
CH4 + O2 ---> CO2 + H20 Balance the equation and get: CH4 + 2O2 ---> CO2 + 2H20
Given 0.15 mols, we are asked to find how many moles of CO2 are produced 0.15mol x what we need (Carbon Dioxide) over what we have already (methane).....
0.15 mol x 1CO2 1 CH4 = 0.15 mol of CO2
Do you get it? Kinda? Not really? Okay let's try some more! How many moles of Aluminum Oxide are required to produce 1.8 mol of pure aluminum? Note: Decomposition Reaction, Balance the Equation
2Al2O3 --> 4Al + 3O2
Given 1.8 mol, looking for Aluminum Oxide moles, given pure aluminum
1.8 mol x 2Al 4Al = 0.90 mol of Aluminum Oxide
Lets do one last one than we're done I promise:
How many moles of hydrogen will be produced if 0.44 mol of CaH2 reacts according to the following equation? CaH2+ 2 H2O --> Ca(OH)2 + 2H2
Today we learned about Stoichiometry. I know the word sounds a little bizarre and frightening but its really not!
Stoichiometry is a branch of chemistry that deals with the quantitative (numbers) analysis of chemical reactions.
It is a generalization of mole conversions to chemical reactions
understanding the 6 types of chemical reactions is the basis of stoichiometry
THE 6 TYPES OF REACTIONS:
Synthesis (formation)
Decomposition
Single Replacement (SR)
Double Replacement (DR)
Neutralization
Combustion
We shall now go through each reaction in further detail.... ready?
^Your reaction will soon change
SYNTHESIS:
A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:
A + B ---> AB
DECOMPOSITION:
A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:
AB ---> A + B
Example: 2 H2O ---> 2 H2 + O
SINGLE REPLACEMENT:
This is when one element trades places with another element in a compound. These reactions come in the general form of:
A + BC ---> AC + B (A IS A METAL)
OR
A +BC---> C+ BA (A IS A NON-METAL)
One example of a single replacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:
Mg + 2 H2O ---> Mg(OH)2 + H2
DOUBLE REPLACEMENT:
This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:
AB + CD ---> AD + CB
One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:
Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
CaSO4+ Mg(OH)2--> Ca(OH)2+ MgSO4 *remember that in double replacement reactions, the metal always go first! in the example of: AgNO3 + NaCL ---> AgCl +NaNO3
Na is the metal and NO3 is the non-metal even though the order is AB+ CD --> AD+ BC we would think that NO
3 goes first but it doesnt!
NEUTRALIZATION:
Also known as Acid-base neutralization: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water (note water can be written as HOH):
HA + BOH ---> H2O + BA
One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:
HBr + NaOH ---> NaBr + H2O
COMBUSTION:
A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:
C10H8 + 12 O2 ---> 10 CO2 + 4 H2O
See that wasn't so hard now was it? High five for effort... lol
Here are a couple of questions for you to try! List what type of reactions they are. The answers are on the bottom.
Percent Composition - The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.
THE PERCENTAGE BY MASS OF AN ELEMENT IN A COMPOUND IS ALWAYS THE SAME.
- to find the percentage by mass, determine the mass of each element present in one mole.
The percent composition (percentage composition) of a compound is a relative measure of the mass of each different element present in the compound.
To calculate the percent composition of a component in a compound:
1. Find the molar mass of the compound by adding up the masses of each atom in the compound using the periodic table. 2.Calculate the mass due to the component in the compound you are for which you are solving by adding up the mass of these atoms. 3.Divide the mass due to the component by the total molar mass of the compound and multiply by 100.
