What is stoichiometry?
Quantitative analysis; the measurement and relationship of quantities involved in chemical reactions
Where does the word stoichiometry come from?
comes from greek words:
- stoicheion (element)
- metron (measure)
What assumptions about reactions are made in stoichiometry?
Reactions are:
Stoichiometric- react in whole number mole ratios
quantitative- all reactants are used up
spontaneous- doesn’t require intervention; occurs on its own
fast- has already occured during the calculations
What to measure for each type of substance?
if:
solid- measure mass
dissolves in water- measure a concentration
gas- measure volume
What are mole to mole ratios?
Used when determining number of moles of one substance given the moles of another
What is the mole to mole process?
1) balance the equation
2) determine the given and unknown in the equation
3) use coefficients for the mole ratio of the two substances
How do you know if a problem is mole to quantity?
If given moles of one substance and asked to find mass, concentration, or volume of another substance, it is a mole to quantity problem
- moles are given, so it is possible to directly convert using mole ratio and finish by converting the new moles to the desired quantity
How do you know if a problem is quantity to moles?
When the quantity of one substance such as mass, volume, por concentration is given and you are asekd to find the moles of another, you will perform a quantity to moles calculation
What is the Haber process?
The reaction of nitrogen and hydrogen to produce ammonia
What is solution stoichiometry?
Often required to use concentration and volume to find moles
What is titration?
A process in which a measured amount of a solution is reacted with a known voloume of another soution (with an unkown concentration) until a desired equivalent point is reached
What is the equivalence point?
Point in a titration where ratio of moles of each species involved in the titration equals exactly the ratio of the coefficients of the species in the balanced reaction equation
How is the equivalence point recognized?
An indicator changing oclor is used; it is chosen so that the point the acidic solutin is exactly neutralized by the added NaOH
What is buffering?
Where the acid is neutralizing the base (as soon as the buffer is used up, pH shoots up)
What does the law of conservation of mass have to do with stoich?
It states “mass cannot be created no destroyed…”
quantitative analysis or precipitation analysis can verify this law
What is a limiting reagent?
The compound that is completely used up first in a chemical reaction
What is used to identify reagents?
The flame test or litmus tests
How are quantities of a specific substance in a sample found?
Titrations or precipitation mass can be used
What are reduced yields?
The reactants may not all react
Why might reduced yields happen?
- not all pure material actually reacts or there are insufficient reaction conditions
- some products are lost during the procedure (solvent extraction or filtration)
What are increased yields?
also possible to have greater than 100% yield; may be done to a variety of issues
Why might increased yields happen?
- contaminated product and impurities present
- products may not be completely dried
What are the three ways to use %yield?
- find the %yield, given the mass of reactant used and mass of product formed
- find the mass of product formed, given the mass of reactant used and the %yield
- find the mass of reactant used, given the mass of product formed and the %yield
What is percent puyrity?
If less than the expected amount of a product is produced, it is possible reactants which are less than 100% pure were used
