Unit 3 - Stoichiometry Flashcards
Molecular formula
The number and type of different atoms in a molecule e.g. CO2
Empirical formula
Simplest whole number ratio for different atoms e.g. H2O2 = OH
Valency
Number of electrons gained or lost
Valency of all groups
- Group I = 1
- Group II = 2
- Group III = 3
- Group IV = 4
- Group V = 3
- Group VI = 2
- Group VII = 1
- group VIII = 0
Ionic compound features
- Ions are charged to get full outer shells
- Compounds final charge must be neutral e.g. k+ + F- = KF
Word equation
Chemical names of all reactants and products
Symbol equation
Names of substances are replaced by element symbols
Polyatomic ions
Ions that have more than one element, e.g. SO4, covalently bonded but unequal protons and electrons
Charges of polyatomic ions
- Hydroxide/OH = 1-
- Carbonate/CO3 = 2-
- Chlorate/ClO4 = 1-
- Nitrate/NO3 = 1-
- Sulfate/SO4 = 2-
Law of conservation of mass
In a reaction the mass of the reactants will equal the mass of the products - mass is conserved
State symbols
- Solid = (s)
- Liquid = (l)
- Gas = (g)
- Aqueous = (aq)
Notation for multiple molecular ions
Brackets around ion with amount e.g. Al(NO3)3
Ammonium
NH4 = 1+
Ammonia
NH3
Relative atomic mass
Every atom’s mass is relative to 1/12th of carbon - 12
Symbol for relative atomic mass
Ar
Relative molecular mass
The mass of all atoms in a compound or molecule - can be used for ionic compounds
Symbol for relative molecular mass
Mr
Avogadro’s constant
1 mole of a substance has 6.02 x 10^23 atoms in it
Relationship with moles and Ar or Mr
1 mole of a substance is weighs its Ar or Mr in grams e.g. 1 mole of H20 = 18g
Mole, mass and Mr equation
- Mass = Moles x Mr
- Moles = Mass ÷ Mr
- Mr = Mass ÷ Moles
Molar gas volume law
Under same temperature and pressure conditions, equal volumes of different gasses contain an equal number of molecules
Molar gas volume constant
1 mole of a gas = 24dm^3 = 24000cm^3 = 0.024m^3
Room temperature and pressure conditions
25˚C and 1 atmospheric pressure
moles and gas volume equation
- Moles = Gas volume ÷ 24
- Gas volume = moles x 24
Concentration equation (mass and volume)
- Concentration = Mass ÷ Volume
- Mass = Concentration x Volume
- Volume = Mass ÷ Concentration
Molar concentration
The amount of moles of a substance dissolved in 1dm^3
Concentration equation (moles and volume)
- Concentration = Moles ÷ Volume
- Moles = Concentration x Volume
- Volume = Moles ÷ Concentration
Titrations
Used for neutralizing an acid or alkali, can be used to find an unknown volume
Limiting reagent
The reactant that is completely used in the reaction and controls the amount of product formed
Excess reagent
The reactant that is left over at the end of the reaction
Theoretical yield
Moles of product in a balanced equation
Actual yield
Moles or total mass obtained experimentally
Percentage yield
Percentage of theoretical yield obtained experimentally
Percentage yield equation
Percentage yield = (Actual yield ÷ Theoretical yield) x 100
Percentage purity of a substance equation
Percentage purity = (Mass of pure product ÷ Mass of impure product) x 100
Steps to ionic equations
1.Identify solids, liquids or gases ( can’t be changed)
2.Identify the ions of the aqueous substances
3.Cross out any ions that appear on both sides of the equation
4.Rewrite the equation without including the species you crossed out
Spectator ion
An ion that remains unchanged throughout a chemical reaction
Steps to finding ratios in a compound
1.Find the atomic mass of each element
2.Divide the percentages of the elements in the compound by their masses
3.Divide these numbers by the smallest value to find the ratio
