unit 3 test Flashcards
STOICHHH
what is a limiting reagent/ reactant?
reactant that limits the amount of a substance that can be created
how do you know when you have a limiting reagent question?
the problem gives you the mass for each reactant.
how to find the moles using mass?
n = m/M
how do you know when a reaction is finished?
the reaction is ended, there is no more of one reactant or no more changes are happening.
what is stoichiometry?
used to predict the amount of a product in a reaction.
what is a mole ratio?
helps us find how many moles of an unknown substance there are. set up with a known ratio and an unknown ratio.
how do you use a mole ratio?
set up an unknown ration with X unknown on the top, on the other side of the ratio use the same reactants using the molecules in the balanced chemical equations. multiply the number you found for # of mols of a reactant by the top of your known ratio and divide by the bottom of the ratio. hope that makes sense :)
what is the strategy for stoichiometry?
number of moles are the key
* start with a balanced chemical equation.
mass A/ Molar mass A -> mol A – mol ratio–> mol B X molar mass B–> mass B
what is a hydrate?
in an ionic compound that has a crystal like structure (all ionic compounds), each unit has an associated amount of water molecules in it.
how do you find %H2O
mass of H2O/mass of hydrated compound
what is a hydrate with water removed called?
an anhydrous compound
what is an emperical formula?
the simplest formula such as CH, there are many molecular formulas containing CH, but CH is the simplest form of it.
what is a molecular formula?
the actual formula, makes up a formula unit depending in the atoms of each element.
what is the law of definite proportions?
also known as the law of constant composition, states that all samples of a compound have the same proportions by mass.
what is the percentage composition?
the relative mass of each element in the compound.
what is the emperical formula rhyme?
percent to mass
mass to mole
divide by small
multiply til whole.`
how to find the emperical formula using % composition
Assume you have 100g of a substance, determine the number or mol in each element from their new mass given,
determine the lowest number of mols in the denominator.
how to find the chemical formula of a hydrate?
write out givens and required, find the molar mass of water, find mols of water, find the mols of other compound, find the ratio of H2O:element
how do you go from number of atoms to mols to mass? (diagram thing but crudely formatted bc i dont want to pay for premium)
< X Na X M>
N (things)———— n (mols) ——— m (mass)
/ Na >
how to do significant digits?
good lord if i know just make a guess maybe like 4 who knows. if you know hoy to plz let me know thanks.
wait i see how to do sig. dig.
-non zero digits in your starting measurement are valid.
-zeros between non zeroes such as 101 are significant
-zeroes to the left of non zeroes are only placeholders, and therefore are not significant.
numbers that are counted, such as an apple, are exact therefore infinite sig. digits.
what is the value of avogadros contant?
6.022X10^23.
what is percent yield?
a way of comparing the experimental value to the theoretical yield, measures the efficiency of a reaction.
how do you measure the % yield?
actual yield over theoretical yield X 100
what is theoretical yield?
the calculated quantity based on stoichometry.
what is actual yield?
gathered experimentally.
how to find % yield?
need a mass of a reactant and product. find mols of each.find mass from mols, find yield with given weight and found weight.
what is molar mass?
the mass of one mol of a substance. can be found using periodic table. units of g/mol.
how to find molecular formula
find emperical formula by assuming 100g of the compoiuund.divide by molar mass to find mols. divide by the smallest. find the mass of compound, divide by given mass of the 1 mol of compound. makes sense?
what causes % yield to be less than 100%
incomplete reaction, inability to gather all of the product, impure reactant, competeing side reaction, incomplete transfer.
what causes % yield to be more than 100%
a competing side reaction, or the product is wet. (water)
when do you have to find a LR?
when you have a defined amount of two products
how do you find moles using things or avocado?
n = N/NA
what are two factors that influence the certainty of a measurement?
systematic error (measuring tool) and random error (made by the measurer)
how do u find the ratio of water in hydrate?
divide mole of water by mole of compound.
