C4 - chemical calculations Flashcards
how do you figure out relative formula mass
add together the relative atomic masses of the elements
what is a mole
the relative atomic mass or relative formula mass of any substance expressed in grams
what is avogadros constant
6.02 x 10^23
what is the equation linking moles and mass
number of moles = mass/Ar
OR
number of moles = mass/Mr
what is the equation for mass using the amount of moles
mass = number of moles x Ar
mass = number of moles x Mr
what do balanced symbol equations tell you
the number of moles of a substance involved in a chemical reaction
what can you use balanced symbol equations for
calculating masses of reactants and products in a chemical reaction
what is the limiting reactant
the reactant that gets used up first in a reaction
NOT in excess
what is the yield of a chemical reaction
the mass of products that a chemical reaction produces
what is the equation for percentage yield
percentage yield = ((actual mass of product produced)/(maximum theoretical mass of product possible)) x100
what are the factors affecting percentage yield
reversible reaction
reactants may react to give unexpected products
some product may be lost in handling or left in apparatus
some desired product may be lost in separation from mixture
what is atom economy
a measure of the extent to which the atoms in the starting materials end up in the desired product
what is the equation for percentage atom economy
percentage atom economy = Mr of desired product/sum of Mr of reactants x 100
why is it important to maximise atom economy
to conserve earths resources and minimise pollution
what is the equation for concentration
concentration = amount of solute/volume of solution
what should you do if you are working in cm^3
convert to dm^3 by dividing it by 1000
OR
use concentration equation with the cm^3 then x1000
how can you increase the concentration of an aqueous solution
adding more solute and dissolving it in the same volume
evaporating off some of the water from the solution
what do an acid and an alkali react together to make
neutralise eachother
a salt and a water
what is titration
a method used to measure the exact volumes of acid and alkali needed to react with eachother
what is the end point in titration
when the reaction between an acid and an alkali is complete
what do you use an acid/base indicator for
show the end point of the reaction
what could you use titration to find
the unknown concentration of a solution
what is the equation for the number of moles of gas
number of moles of gas = volume of gas (dm^3) / 24 dm^3
OR
volume of gas (cm^4) / 24000 cm^3
what is the volume of 1 mole of gas at any room temperature and pressure
24 dm ^3
what is the meniscus
the dip that occurs in the solution in the burette
