c3 quantitative chemistry Flashcards
What is the law of conservation of mass?
no, atoms are lost or made during a chemical reaction, so the mass of the products will equal the mass of the reactants
what charges will the ions from different metal groups be, and what are the exceptions
(group)+
eg mg2+
transition metals can form ions of different charges
what charges will the ions from different non-metal groups be, and what are the exceptions
(8-group)-
eg Br-
hydrogen and ammonium are positive
how do you find the formula of ionic compounds
in ionic compound, the charges on the ions have to cancel out to leave an overall charge of 0
cross multiply - charge from one ion becomes mass of other ion
how to find formula of sodium chloride
Na+ Cl-
(1 charges cancel out)
NaCl
how to find formula of calcium hydroxide (Ca2+ and OH-)
2 hydroxide needed to cancel single calcium
Ca(OH)2
what is relative atomic mass and what is the symbol
Ar
average mass of isotopes in an element, to take into account the abundance of each isotope
(top number of element)
what is relative formula mass and what is the symbol
Mr
sum of the relative atomic masses of the atoms
how to find the percentage mass of one element in a compound
Mr of compound
x 100
what actually is a mole
a measurement
eg like saying “a billion”
how do you determine how much is 1 mole of atoms
the relative atomic mass of the element, in grams, will be equal to 1 mole of atoms of that element
eg carbon Ar = 12, so
12g of carbon = 1mol carbon atoms
= 6.02 x 10^3 atoms
how to calculate moles
mass/Mr
how to balance an equation using moles
- use mass/mr to find moles of each compound, and write it as a large number
- divide all large numbers by smallest number to get the smallest ratio
how to calculate the number of moles of an atom, in a given number of moles of the molecule the atom is in
number of atoms are in 1 molecule = number of moles of atoms in 1 mole of molecules
how to calculate the number of atoms in 1 mole of a molecule
calculate number of atoms
1 mol = 6.02 x 10^23 molecules
number of atoms x 6.02x10^23
how to calculate number of atoms in a given mass of an element
calculate moles using mass/Mr
number of moles of an atom = 6.02x10^23 atoms
so number of atoms = number of moles x 6.02x10^23
how to calculate number of atoms in a given mass of a compound
calculate moles using mass/Mr
number of moles of the molecule = 6.02x10^23 molecules
so number of atoms = number of atoms in 1 molecule x 6.02x10^23
how to calculate masses of reactants and products in a chemical reaction
use mol = mass/mr to find mol of reactant
multiply by scale factor of reactant to product
use mass = mol x mr to find mass
what assumptions have been made when calculating mass of reactants & products of a chemical in a chemical reactiom
the other chemical is unlimited
how to calculate masses of reactants and products in a chemical reaction, taking into account a limiting reactant
find moles of product using limiting reactant x scale factor of moles
calculate mass as normal
what is the volume of one mole of gas, and under what conditions
24dm^3
at room temp 20 degrees, and room pressure 1 atmosphere
equation for volume of a gas
number of moles x 24
how to find volume of a gas from mass and mr of element
find moles using mass/mr
x 24
how to find volume of gas in a chemical reaction
find moles using mass/mr
multiply by mol scale factor to find moles of gas product
x 24
what assumptions have been made when calculating volume of a gas from a chemical reaction
gas is at room temp and pressure
what is a limiting reactant
the reactant that is fully used up
what is Avogadros constant?
6.02 x10^23
what is concentration and what is it measured in
the mass of a solute/number of moles in a solute in a given volume of solution
g/dm^3 or mol/dm^3
how to find conc of a solution in a reaction
- write c=, v=, and m= under both reactions and fill in conc, vol, and mol
- find missing values using mol = conc x vol
- multiply mol by mol scale factor to find moles of other reactant
- find missing values
what is a solute
chemical that is dissolved in a solvent
how does mass of solute and volume of solution affect conc
increase mass, constant volume = increase conc
increase volume, constant mass = decrease conc
what is 100% yield
when all of the starting mass reacts to form the product
why is 100% yield not often achieved
- there may be unexpected side reactions
- some product may be lost when it is separated from reaction mixture
- reversible reactions do not go to completion
how to calculate percentage yield
maximum theoretical mass of product
x 100
how to calculate percentage yield for a reaction
calculate theoretical mass using mol x mr
maximum theoretical mass of product
x 100
what is atom economy
a measure of the amount of reactants that end up as useful product
why is atom economy important
- high atom economy saves money, as low ones use up more resources more quickly
- minimising waste increases sustainability
how do we deal with unwanted side products
try to find uses for them, eg in other reactions, to not waste money
how to calculate atom economy
sum of mr of all reactants
x 100
what is 1dm^3 in centimetres
1000 cm^3
