Chapter 2 - Amount of Substance Flashcards
define relative atomic mass
the average mass of an atom relative to one twelfth of the average mass of a carbon 12 atom
average mass of one atom of an element*12/mass of one carbon-12 atom
what is relative molecular mass
the same as relative atomic mass but the average mass of one molecule
you can find this mass by adding up all the relative masses in a molecule
what is relative formula mass
a way to measure the mass of one repeating unit in an ionic compound because they dont exist as molecules but rather a giant lattice
what is the avogadro constant
6.022 x 10^23
what is the significance of the avogadro constant
the number of atoms or molecules in one mole of a substance
one mole of a substance is equal to the Mr or Ar in grams
The Avogadro constant or Avogadro number is the number of atoms in 12 g of carbon-12.
how can you find the mass of one atom of a substance in Kg
(mass/1000)/6.022*10^23
what is a solute
the substance that is dissolved in a solvent
what is a solvent
the substance that dissolves the solute
what is a solution
a combination of a dissolved solute and a solvent
what does concentration indicate
the amount of a substance in one dm^3 of said substance
what is boyles law
as long as the temperature is constant, the product of the pressure and the volume is constant
what is charles’ law
The volume is proportional to the temperature as long as the pressure
remains constant
pressure/temperature = constant
what is the constant volume law
The pressure is proportional to the temperature as long as the volume
remains constant.
pressure/temperature = constant
what is the ideal gas equation
pV=nRT
what is back titration
a substance of an unknown concentration is titrated with a substance of a known concentration in excess.
the resulting mixture is titrated with another substance of known conc.
the moles reacted can be subtracted from the total moles used to find how many moles reacted in the initial reaction.
this can then be used to find the concentration of the unknown substance.
when are back titratoins used
when the reaction is slow, the substance is not pure, the reaction is difficult to observe, the analyte is a non-soluble solid
when do we use relative formula mass
when we have a giant covalent or ionic lattice
define a mole
6.022 x 10^23 units of a substance
define concentration
the amount of a solute (in g or mol) per unit volume (always dm^3)
what assumptions are made for the motion of gas particles
Gas particles move rapidly and randomly.
The volume of the actual gas particles is negligible compared to empty space between them.
There are no intermolecular attractions or repulsions.
Collisions between particles are elastic - no energy is lost.
The average kinetic energy of particles depends only on their temperature.
what is an ideal gas
a gas which obeys all the assumptions made in kinetic theory and can be exactrly represented using the ideal gas equation at room temp and pressure
what is the difference between the empirical and molecular formula
empirical formula gives the lowest whole number ratio of elements present in a compound while the molecular formula shows the actual number of atoms of each element present in a compound
how can you calculate empirical formula from percentage composition by mass
assume the total sample size is 100g
find the moles of each element present by dividing the percentage by the Ar
find the lowest whole number ratio of the moles
how can you find the molecular formula from the empirical formula
calculate the empirical formula mass
then divide the molecular formula mass by the empirical formula mass
multiply the ratio of atoms in the empirical formula by the resulting number
how do you write an ionic equation
write out each ion present (remember that only aqueous solutions will separate in to ions, keep solids, liquids and gases the same)
cancel out ions that appear on both sides of the equation
check the charges are balanced
what is the limiting reactant and what is its significance
the reactant which runs out first, the one that doesnt is “in excess”
the limiting reactnace puts a “limit” on the amount of products that can be formed.
what does atom economy measure
how efficient a chemical reaction is at incorporating the reactants into the desired product
atom economy measures the percentage of reactant atoms that end up in the final desired product
equation for atom economy
mr of desired product / mr of all reactants including their mole ratios x 100
what is the significance of atom econoimy
a high atom economy is more sustainable because it generates less waste and uses raw materials more efficiently. it also reduces costs on separating products and requires lower amounts of reactants.
what is theoretical yield
the maximum mass of a product that could be made in ideal conditions
why is the actual yield always less than the theoretical
some material may not react completely
some products may be lost if they are gaseous, or when transferring substances between containers
side reactions may occur, using up some reactants
formula for percentage yield
actual yield / theoretical yield x 100
what does percentage yield indicate
how efficiently a reaction is carried out
how close the actual mass produced is to the maximum mass produced
Suggest three reasons why the percentage yield of a chemical reaction may be less than 100%.
the reactants may not all react (e.g. because the reaction is very slow or reaches equilibrium)
some of the products may be lost during workup procedures
there may be side reactions, meaning that other products are produced instead
Which sub-atomic particle was discovered by JJ Thomson?
electron
name all the contributions made by Ernest Rutherford to the development of the atomic model.
discovered the nucleus and the proton
