Chapter 1 ~Moles And Equations Flashcards
Definitions, key ideas and formula
Definition of relative atomic mass (Ar)
The relative atomic mass is the weighted average mass of naturally occurring atoms of an element on a scale where an atom of carbon - 12 has a mass of exactly 12 units.
Formula for relative atomic mass of element Y:
Ar [element Y] =
=average mass of one atom of element Y x 12
÷by
Mass of one atom of carbon - 12
Definition of nucleon number
°The total number of neutrons and protons in the nucleus of an atom ⚛
(extra information :the number is written either on top of the element or next to the element e.g. C-14)
Definition of relative isotopic mass
°the mass of a particular isotope of an element on a scale in which an atom of the carbon-12 isotope has a mass of exactly 12 units
Definition of relative formula mass
°the mass of one formula unit of a compound measured on a scale on which an atom of carbon-12 isotope has a mass of exactly 12 units
Definition of relative molecular mass
°the mass of a molecule measure on a scale in which an atom of the carbon-12 isotope has a mass of exactly 12 units
The 3 steps of determining the Ar (relative atomic mass) from a mass spectra :
- Multiple each isotopic mass by its percentage abundance
- add all the figures together
- Divide by 100
The definition for a mole of a substance :
° one mole of a substance is the amount of that substance that has the same number of specific particles (atoms, molecules or ions) as there are atoms in exactly 12g of the carbon-12 isotope
Definition of molar mass
°the mass of one mole of a substance in grams
Definition of Avogadro constant :
°the number of atoms (or ions or molecules or electrons) in a mole of atoms (or ions or molecules or electrons) :it’s numerical value is 6.02 x 10^23 (Ten to the power of 23)
Formula of the number of moles (Mol) =
=Mass of substance (g)÷/
÷molar mass(g.mol^-1)
Formula of mass of a substance in grams =
= n (num moles) x M(molar mass)
Definition of stoichiometry
The mole ratio of the reactants and products in the balanced equation for a reaction
In order to find the mass of products formed in a chemical reaction we use 3 things,
Namely?
- The mass of the reactants
- The molar mass of the reactants
- The balanced equation
Formula for the stoichiometric numbers
=masses in the reactions ÷ by Ar values
Percentage composition by mass =
~(Ar x number of moles of a particular element in a compound)
~÷
~(molar mass of compound)
~x 100
Example : Fe2O3 calculate irons mass %
(Ar values : Fe=55.8, O=16)
(55.8 x 2) / (55.8x2)+(16x3)
Ans x 100
Definition of empirical formula
°simplest whole number ratio
Definition of molecular formula :
°The formula that tells you the actual numbers of each type of atom ⚛ in a molecule
The formula for an ionic compound is always its…..
Empirical formula
The empirical formula can be deduced in 2 methods :
- determining the mass of each element present in a sample of the compound
- From data that gives the percentage composition by mass of the elements in a compound
What 2 things do we need to deduce the molecular formula?
- the relative formula mass of the compound
2. The empirical formula
3 Steps of determining the molecule formula :
- Find the empirical formula mass
- Divide the relative molecular mass by the empirical formula mass to get the determining factor
3.multiply the number of atoms in the empirical formula by the determining factor.
Then you have the molecular formula
Definition of state symbols
°a symbol used in a chemical equation that describes the state of each reactant and product
s-solid
l-liquid
g-gas
aq- aqueous solution
Definition of spectator ions :
°ions present in a reaction mixture that do not take part in the reaction (are on both sides of the ionic equation)
The 4 steps of writing an ionic equation are….
- Write down the full balance equation
- Write down all the ions present. NB!!! Any reactant /product with state symbols : (s), (l), (g) or is a molecule in solution e.g. Cl2 in MgCl2 forms (Mg ^2+ and 2Cl^-) so the chlorine is together.
Does NOT split into ions - cancel spectator ions
- write down equation omitting the spectator ions
What is a precipitation reaction?
A reaction where 2 aqueous solutions react to form a solid-the precipitate
2 steps in writing the ionic equation for a precipitate reaction :
- Write formula of the precipitate as the product
2. Write the ions that go to make up the precipitate as the reactants
How to change cm^3 to dm^3?
By dividing the number of cm^3 by 1000
Formula for concentration (mol dm^3) =
=number of moles(mol) ÷volume(dm^3)
=n/V
Number of moles(mol) =
C x V
Definition of titre:
°in a titration, the final burette reading minus the initial burette reading
The 3 steps of calculating the solution concentration by titration :
- Calculate the moles of acid using the formula
n=m/M
- Us the stoichiometry of the balanced equation to calculate the moles of base
- Then calculate the concentration of base using the formula
c=n/v
*can be visa versa
3 Steps of deducing the stoichiometry by titration :
- Calculate the number of moles of each reagent using the formula
n = C x V (remember in dm^3)
NB!!! if in cm^3 than ÷by 1000
- Deduce the simplest mole ratio
- write the equation
What is a titration?
A (laboratory) method or technique of determining the unknown concentration of a solution by reacting it with a known concentration of a substance.
(an acid and base)
What is the molar gas volume?
24dm^3
Formula for number of moles of a gas, n (mol) =
= V(dm^3) ÷ 24dm^3
Volume of a gas (dm^3) =
Number of moles, n (mol) x 24dm^3
What is a molar (M)?
A measure of concentration, equilavent to mol.dm^-3
