Chemistry: (d) Mole Conversions, Molecular/Empirical Formulas, Stoichiometry, Molarity, Limiting Rea
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Why are moles used?
You can't directly count atoms, moles are used instead
Does the molar masses of 2 difference substances or the number of particles in a mole always remain the same?
number of particles in a mole
What do each of the letters in the ideal gas law (PV=nRT) stand for?
pressureXvolume= number of molesXgas constantXtemperature
In the ideal gas law, what unit must the volume and the temperature always be in?
- Volume: liters
- Temperature: kelvin
What are molecular formulas the same as?
empirical formulas or some whole number multiple of it
What are the three steps to getting a molecular formula?
- 1) get empirical
- 2) divide molar mass from problem by molar mass from the empirical formula
- 3) multiple subscripts by answer to #2
What are the two things empirical formulas show?
- the lowest whole number ratio of elements
- actual numbers of atoms in molecules
What are the four steps for empirical formulas?
- 1) assume % is grams
- 2) convert grams to moles
- 3) divide by smaller number
- 4) multiply to get whole numbers
What is a skeleton equation?
What are the 7 elements that exist as diatomic molecules?
hydrogen, nitrogen, oxygen, florine, chlorine, bromine, iodine
What is the definition of sstoichiometry?
using balanced equations to determine the amounts of R needed to create a specific amount of P
Why do we care about stoichiometry?
- companies use stoichiometry to reduce waste, keep costs down and create products that work
- we use ideas of stoich in everyday lives
What is molarity?
moles of solute per liter of solution
What is a solute? Give an example.
substance which dissolves (like NaCl)
Why do we need molarity?
for aqueous solutions b/c molar mass cannot be used for them
T or F? 100g of NaCl (aq) is different than 100g of NaCl (s).
What is the equation for molarity?
M=moles over liters
How can you tell if the problem is a limiting reagent one?
more than one reactant amount is given
How do you do a limiting reagent problem?
- convert 1st reagent to product (g)
- convert 2nd reagent to product (g)
- pick lowest one
How can you tell if a problem is one, two or three steps?
- one- moles to moles
- two- moles to something else or something else to moles
- three- no moles mentioned
What does percent yield measure?
how much of the expected product you actually get
What would you like to do?
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