Stoichiometry Flashcards
molecular formula of a compound definition
the number and type of atoms in one molecule
How do you find Mr
Add the atomic masses of the atoms in the molecule - don’t forget if there’s a small number below the element you need to multiply its atomic mass by that number
How do you deduce the formula of a simple molecular compound from a model or diagram
count the atoms of each element, then write the chemical formula using the element symbols and subscripts to indicate the number of each ato
How do you construct symbol equations with state symbols, including ionic equations
first write the balanced symbol equation, then add state symbols (s, l, g, aq) to indicate the physical state of each substance, and finally, for ionic equations, identify and represent only the ions that participate in the reaction
What is Ar
Atomic mass
How do you find Ar from isotopic abundance
Ar = ( %1 * mass1 ) + ( %2 * mass2 ) / 100
Percentage yield
% yield = actual mass of product made / theoretical mass * 100
Percentage purity
% purity = mass of pure substance / total mass * 100
Moles (n)
m/mr
Concentration
C = n/v
Volume of a gas
V of gas = n * 24 dm3
Cm3 to dm3
divide by 1000
What solutions do ions exist in
Aqueous
Net ionic equations + spectator ions
1 - split all ions (in aqueous form)
2 - write out charge and state of all ions
3 - cross out ions which are equivalent on both sides of the reaction (theses are the spectator ions)
4 - ionic equation is everything left over
Empirical formula
- convert the given percentages or masses of elements into moles ( % or mass / atomic mass Ar )
- divide each by the smallest number of moles to get a whole-number ratio
What do neutralisation reactions produce
Water and salt
Metal + acid products
Hydrogen + salt
Metal + oxide
Metal oxide
Metal carbonate + acid
Salt + water + carbon dioxide
3 must know acids
Hydrochloric acid - HCl
Sulfiric acid - H2SO4
Nitric acid - HNO3
Hydroxide
-OH
Sulfate
SO4 2-
Law of conservation of mass
Mass cannot be created or destroyed
Limiting and excess reagents
1 - calculate the number of moles
2 - compare as a ratio of moles : find the simplest ratio
3 - whichever is greater is the reagent in excess, other is limiting
Litres to ml
Times 1000
ml to cm3
Same
How do you find Ar from isotopic abundance
Ar = ( %1 * mass1 ) + ( %2 * mass2 ) / 100
Molecular formula
Molecular formula = Mr/empirical formula
